High strength and high toughness metal and method of producing the same

Abstract

This invention provides a high-strength and high-toughness metal which has strength and toughness each high enough to be put to practical use in expanded applications of magnesium alloys, and a process for producing the same. The high-strength and high-toughness metal is a magnesium alloy comprising a crystal structure containing an hcp-structure magnesium phase and a long-period layered structure phase. At least a part of the long-period layered structure phase is in a curved or flexed state. The magnesium alloy comprises a atomic % of Zn and b atomic % of Gd with the balance consisting of Mg.

1 . A high strength and high toughness metal comprising a magnesium alloy having a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase, 
 wherein at least a part of said long-period stacking ordered structure phase exists in a lamellar form with a 2H structure Mg phase.    
   
   
       2 . A high strength and high toughness metal in which a plastically worked product produced by subjecting a magnesium alloy to a plastic working has a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase, 
 wherein at least a part of said long-period stacking ordered structure phase exists in a lamellar form with a 2H structure Mg phase.    
   
   
       3 . The high strength and toughness metal according to  claim 1  or  2 , 
 wherein at least a part of said lamellar structure existing in a lamellar form is flexed or bend.    
   
   
       4 . A high strength and high toughness metal comprising a magnesium alloy having a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase, 
 wherein at least a part of said long-period stacking ordered structure phase is flexed or bend.    
   
   
       5 . A high strength and high toughness metal in which a plastically worked product produce by subjecting a magnesium alloy to a plastic working has a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase, 
 wherein at least a part of said long-period stacking ordered structure phase is flexed or bend.    
   
   
       6 . The high strength and high toughness metal according to  claim 2  or  5 , 
 wherein said magnesium alloy before subjecting to a plastic working has a crystal structure having a long-period stacking ordered structure phase in which flexure or bend is not formed.    
   
   
       7 . The high strength and high toughness metal according to any one of claims  1 ,  2  and  5 , 
 wherein a part of a region where said long-period stacking ordered structure phase is flexed or bend contains random grain boundaries.    
   
   
       8 . The high strength and high toughness metal according to any one of claims  1 ,  2 ,  4  and  5 , 
 wherein said long-period stacking ordered structure phase has a dislocation density one-digit smaller than said hcp-Mg phase.    
   
   
       9 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and Y in an amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.5≦ a≦ 5.0;  (1) 1.0≦ b≦ 5.0; and  (2) 0.5 a≦b.   (3)   
   
   
       10 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.2≦ a≦ 5.0;  (1) 0.2≦ b≦ 5.0; and  (2) 0.5 a −0.5≦ b.   (3)   
   
   
       11 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.2≦ a≦ 3.0;  (1) 0.2≦ b≦ 5.0; and  (2)   2   a− 3≦ b.   (3)   
   
   
       12 . The high strength and high toughness metal according to  claim 10 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Tm and Lu in a total amount of “y” atomic %, wherein “y” satisfies the following expressions (4) to (5):     0≦ y≦ 4.8; and  (4) 0.2≦ b+y≦ 5.0.  (5 )   
   
   
       13 . The high strength and high toughness metal according to  claim 9 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4) 0.2≦ b+c≦ 6.0.  (5)   
   
   
       14 . The high strength and high toughness metal according to  claim 10 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4) 0.2≦ b+c≦ 6.0.  (5)   
   
   
       15 . The high strength and high toughness metal according to  claim 9 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0.2≦ c≦ 2.0; and  (4) 0.2≦ b+c≦ 6.0  (5)   
   
   
       16 . The high strength and high toughness metal according to  claim 10 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0.2≦ c≦ 2.0; and  (4) 0.2≦ b+c≦ 6.0  (5)   
   
   
       17 . The high strength and high toughness metal according to any one of  claim 9 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4)   0≦   d≦ 2.0; and  (5) 0.2≦ b+c+d≦ 6.0.  (6)   
   
   
       18 . The high strength and high toughness metal according to  claim 10 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.2≦ b+c+d≦ 6.0.  (6)   
   
   
       19 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and Y in an amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.25≦ a≦ 5.0;  (1) 0.5≦ b≦ 5.0; and  (2) 0.5 a≦b.   (3)   
   
   
       20 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1≦ a≦ 5.0;  (1) 0.1≦ b≦ 5.0; and  (2) 0.5 a− 0.5≦ b.   (3 )   
   
   
       21 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % of Zn and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1≦ a≦ 3.0;  (1) 0.1≦ b≦ 5.0; and  (2) 2 a− 3≦ b.   (3)   
   
   
       22 . The high strength and high toughness metal according to  claim 20 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Tm and Lu in a total amount of “y” atomic %, wherein “y” satisfies the following expressions (4) to (5):     0≦ y≦ 4.9; and  (4) 0.1≦ b+y≦ 5.0.  (5)   
   
   
       23 . The high strength and high toughness metal according to  claim 19 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4) 0.1≦ b+c≦ 6.0.  (5)   
   
   
       24 . The high strength and high toughness metal according to  claim 20 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4) 0.1≦ b+c≦ 6.0.  (5)   
   
   
       25 . The high strength and high toughness metal according to  claim 19 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1≦ b+c≦ 6.0.  (5)   
   
   
       26 . The high strength and high toughness metal according to  claim 20 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions. (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1≦ b+c≦ 6.0.  (5)   
   
   
       27 . The high strength and high toughness metal according to  claim 19 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0.; and  (5) 0.1≦ b+c+d≦ 6.0.  (6)   
   
   
       28 . The high strength and high toughness metal according to  claim 20 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4)   0≦   d≦ 2.0.; and  (5) 0.1≦ b+c+d≦ 6.0.  (6)   
   
   
       29 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and of at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.2≦ a≦ 5.0;  (1) 0.5≦ b≦ 5.0; and  (5) 0.5 a− 0.5≦ b.   (6)   
   
   
       30 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % of Zn and at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.2 ≦a≦ 3.0;  (1) 0.5 ≦b≦ 5.0.; and  (5) 2 a− 3 ≦b.   (6)   
   
   
       31 . The high strength and high toughness metal according to  claim 29 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4) 0.5 ≦b+c≦ 6.0.  (5)   
   
   
       32 . The high strength and high toughness metal according to  claim 29 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.5≦ b+c≦ 6.0.  (5)   
   
   
       33 . The high strength and high toughness metal according to  claim 29 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.5 ≦b+c+d≦ 6.0.  (6)   
   
   
       34 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1 ≦a≦ 5.0;  (1) 0.25 ≦b≦ 5.0; and  (2) 0.5 a− 0.5 ≦b.   (3)   
   
   
       35 . The high strength and high toughness metal according to  claim 4 , 
 wherein said magnesium alloy contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Gd, Tb, Tm and Lu in an amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1 ≦a≦ 3.0;  (1) 0.25 ≦b≦ 5.0; and  (2) 2 a− 3 ≦b.   (3)   
   
   
       36 . The high strength and high toughness metal according to  claim 34 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfy the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4)   0.25   ≦b+c≦ 6.0.  (5)   
   
   
       37 . The high strength and high toughness metal according to  claim 34 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfy the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.25 ≦b+c≦ 6.0.  (5)   
   
   
       38 . The high strength and high toughness metal according to  claim 34 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.25≦ b+c+d≦ 6.0.  (6)   
   
   
       39 . The high strength and high toughness metal according to  claim 29 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Dy, Ho and Er in a total amount of larger than 0 atomic % to 1.5 atomic % or less.    
   
   
       40 . The high strength and high toughness metal according to  claim 34 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Dy, Ho and Er in a total amount of larger than 0 atomic % to 1.5 atomic % or less.    
   
   
       41 . The high strength and high toughness metal according to  claim 29 , 
 wherein said magnesium alloy contains Y in an amount of larger than 0 atomic % to 1.0 atomic % or less.    
   
   
       42 . The high strength and high toughness metal according to  claim 34 , 
 wherein said magnesium alloy contains Y in an amount of larger than 0 atomic % to 1.0 atomic % or less.    
   
   
       43 . The high strength and high toughness metal according to  claim 29 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of less than 3 atomic %.    
   
   
       44 . The high strength and high toughness metal according to  claim 34 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of less than 3 atomic %.    
   
   
       45 . The high strength and high toughness metal according to  claim 9 , 
 wherein said magnesium alloy is produced by the following manner:    a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements; and    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       46 . The high strength and high toughness metal according to  claim 10 , 
 wherein said magnesium alloy is produced by the following manner:    a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements; and    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       47 . The high strength and high toughness metal according to  claim 19 , 
 wherein said magnesium alloy is produced by the following manner:    a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements; and    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       48 . The high strength and high toughness metal according to  claim 20 , 
 wherein said magnesium alloy is produced by the following manner:    a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements; and    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       49 . The high strength and high toughness metal according to  claim 29 , 
 wherein said magnesium alloy is produced by the following manner:    a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements; and    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       50 . The high strength and high toughness metal according to  claim 34 , 
 wherein said magnesium alloy is produced by the following manner:    a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements; and    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       51 . The high strength and high toughness metal according to  claim 9 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B and C in a total amount of larger than 0 atomic % to 2.5 atomic % or less.    
   
   
       52 . The high strength and high toughness metal according to  claim 9 , 
 wherein said magnesium alloy contains at least one precipitate selected from the group consisting of a precipitate comprising compound of Mg and rare-earth element, precipitate comprising compound of Mg and Zn, precipitate comprising compound of Zn and rare-earth element and precipitate comprising compound of Mg, Zn and rare-earth element.    
   
   
       53 . The high strength and high toughness metal according to  claim 9 , 
 wherein said magnesium alloy has a grain size of 100 nm to 500 μm.    
   
   
       54 . A high strength and high toughness metal having a composition of general formula of Mg (100-x-y) Y x Zn y  (1<x<5, 0.3<y<6; x and y represent atomic %) and having a crystal structure having an average grain size of 1 μm or smaller, 
 wherein said Mg (100-x-y) Y x Zn y  is produced in the following manner:    a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material and made into liquid form;    the rare-earth alloy in liquid form is rapidly solidified into powder, thin band or thin wire; and    the powder, thin band or thin wire is solidified so as to be applied with shear.    
   
   
       55 . The high strength and high toughness metal according to  claim 45 , 
 wherein said rare-earth alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of 50 atomic % or more and at least one rare-earth element other than Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of less than 50 atomic %.    
   
   
       56 . The high strength and high toughness metal according to  claim 54 , 
 wherein said rare-earth alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of 50 atomic % or more and at least one rare-earth element other than Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of less than 50 atomic %.    
   
   
       57 . A method of producing a high strength and high toughness metal comprising: 
 a step for preparing a magnesium alloy having a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase, wherein at least a part of said long-period stacking ordered structure phase exists in a lamellar form with a 2H structure Mg phase; and    a step for subjecting said magnesium alloy to a plastic working to produce a plastically worked product which keeps a lamellar structure existing in a lamellar form.    
   
   
       58 . A method of producing a high strength and high toughness metal comprising: 
 a step for preparing a magnesium alloy having a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase; and    a step for subjecting said magnesium alloy to a plastic working to produce a plastically worked product in which at least a part of said long-period stacking ordered structure phase is flexed or bend.    
   
   
       59 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and Y in an amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.5 ≦a≦ 5.0;  (1) 1.0 ≦b≦ 5.0; and  (2) 0.5 a≦b.   (3)   
   
   
       60 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):       0.2   ≦a≦ 5.0;  (1) 0.2 ≦b≦ 5.0; and  (2) 0.5 a− 0.5 ≦b.   (3)   
   
   
       61 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.2 ≦a≦ 3.0;  (1) 0.2 ≦b≦ 5.0; and  (2) 2 a− 3 ≦b.   (3)   
   
   
       62 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Tm and Lu in a total amount of “y” atomic %, wherein “y” satisfies the following expressions (4) to (5):     0 ≦y≦ 4.8; and  (4) 0.2 ≦b+y≦ 5.0.  (5)   
   
   
       63 . The method of producing a high strength and high toughness metal according to  claim 59 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 3.0; and  (4) 0.2 ≦b+c≦ 6.0.  (5)   
   
   
       64 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4) 0.2 ≦b+c≦ 6.0.  (5)   
   
   
       65 . The method of producing a high strength and high toughness metal according to  claim 59 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.2 ≦b+c≦ 6.0.  (5)   
   
   
       66 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.2 ≦b+c≦ 6.0.  (5)   
   
   
       67 . The method of producing a high strength and high toughness metal according to  claim 59 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.2 ≦b+c+d≦ 6.0.  (6)   
   
   
       68 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.2 ≦b+c+d≦ 6.0.  (6)   
   
   
       69 . A method of producing a high strength and high toughness metal comprising: 
 a step for preparing a magnesium alloy having a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase, wherein at least a part of said long-period stacking ordered structure phase exists in a lamellar form with a 2H structure Mg phase;    a step for cutting said magnesium alloy to form a chip-shaped cutting product; and    a step for subjecting said chip-shaped cutting product to a plastic working to solidify and thereby to produce a plastically worked product keeping said lamellar structure existing in a lamellar form.    
   
   
       70 . A method of producing a high strength and high toughness metal comprising: 
 a step for preparing a magnesium alloy having a crystal structure having an hcp-Mg phase and a long-period stacking ordered structure phase;    a step for cutting said magnesium alloy to produce a chip-shaped cutting product; and    a step for subjecting said chip-shaped cutting product to a plastic working to solidify and thereby to produce a plastically worked product in which at least a part of said long-period stacking ordered structure phase is flexed or bend.    
   
   
       71 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and Y in an amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.25 a≦ 5.0;  (1) 0.5 ≦b≦ 5.0; and  (2) 0.5 a≦b.   (3)   
   
   
       72 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1 ≦a≦ 5.0;  (1) 0.1 ≦b≦ 5.0; and  (2) 0.5 a− 0.5 ≦b.   (3)   
   
   
       73 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Dy, Ho and Er in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1 ≦a≦ 3.0;  (1) 0.1 ≦b≦ 5.0; and  (2) 2 a− 3 ≦b.   (3)   
   
   
       74 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Tm and Lu in a total amount of “y” atomic %, wherein “y” satisfies the following expressions (4) to (5):     0 ≦y≦ 4.9; and  (4) 0.1 ≦b+y≦ 5.0.  (5)   
   
   
       75 . The method of producing a high strength and high toughness metal according to  claim 71 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 3.0; and  (4) 0.2 ≦b+c≦ 6.0.  (5)   
   
   
       76 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 3.0; and  (4) 0.2 ≦b+c≦ 6.0.  (5)   
   
   
       77 . The method of producing a high strength and high toughness metal according to  claim 71 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1≦ b+c≦ 6.0.  (5)   
   
   
       78 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0.  (5)   
   
   
       79 . The method of producing a high strength and high toughness metal according to  claim 71 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and “d” satisfy the following expressions (4) to (6):     0 ≦c≦ 3.0;  (4) 0 ≦d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       80 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       81 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):       0.2   ≦a≦ 5.0;  (1) 0.5 ≦b≦ 5.0; and  (2) 0.5 a− 0.5 ≦b; and,   (3)   the method further comprising:    a step for subjecting said magnesium alloy to a heat treatment between said step for preparing a magnesium alloy casting product and said step for producing a plastically worked product.    
   
   
       82 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Gd, Tb, Tm and Lu in an amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.2 ≦a≦ 3.0;  (1) 0.5 ≦b≦ 5.0; and  (2) 2 a− 3 ≦b; and,   (3)   the method further comprising:    a step for subjecting said magnesium alloy to a heat treatment between said step for preparing a magnesium alloy casting product and said step for producing a plastically worked product.    
   
   
       83 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 3.0; and  (4) 0.5 ≦b+c≦ 6.0.  (5)   
   
   
       84 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.5 ≦b+c≦ 6.0  (5)   
   
   
       85 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.5 ≦b+c+d≦ 6.0.  (6)   
   
   
       86 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1 ≦a≦ 5.0;  (1) 0.25 ≦b≦ 5.0; and  (2) 0.5 a− 0.5 ≦b;  and,  (3)   the method further comprising:    a step for subjecting said magnesium alloy to a heat treatment between said step for preparing a magnesium alloy casting product and said step for producing a chip-shaped cutting product, or, between said step for producing a chip-shaped cutting product and said step for producing a plastically worked product.    
   
   
       87 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains Zn in an amount of “a” atomic % and at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of “b” atomic %, wherein “a” and “b” satisfy the following expressions (1) to (3):     0.1 ≦a≦ 3.0;  (1)   0.25≦   b≦ 5.0; and  (2) 2 a− 3 ≦b;  and,  (3)   the method further comprising:    a step for subjecting said magnesium alloy to a heat treatment between said step for preparing a magnesium alloy casting product and said step for producing a chip-shaped cutting product, or, between said step for producing a chip-shaped cutting product and said step for producing a plastically worked product.    
   
   
       88 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 3.0; and  (4) 0.25 ≦b+c≦ 6.0.  (5)   
   
   
       89 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.25 ≦b+c≦ 6.0  (5)   
   
   
       90 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0 ≦c≦ 3.0;  (4) 0 ≦d≦ 2.0; and  (5) 0.25≦ b+c+d≦ 6.0.  (6)   
   
   
       91 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of less than 3 atomic %.    
   
   
       92 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said magnesium alloy contains at least one element selected from the group consisting of Gd, Tb, Tm and Lu in a total amount of less than 3 atomic %.    
   
   
       93 . The method of producing a high strength and high toughness metal according to any one of claims  59 ,  60 ,  71 ,  72 ,  81  and  86 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 3.0; and  (4) 0.1 ≦b+c≦ 6.0.  (5)   
   
   
       94 . The method of producing a high strength and high toughness metal according to  claim 59 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       95 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       96 . The method of producing a high strength and high toughness metal according to  claim 71 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       97 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       98 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       99 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       100 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0≦ c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       101 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “c” atomic %, wherein “c” satisfies the following expressions (4) to (5):     0 ≦c≦ 2.0; and  (4) 0.1 ≦b+c≦ 6.0  (5)   
   
   
       102 . The method of producing a high strength and high toughness metal according to  claim 59 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0 ≦d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       103 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       104 . The method of producing a high strength and high toughness metal according to  claim 71 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0 ≦d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       105 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       106 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       107 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0 ≦d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       108 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Tb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0≦ d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       109 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Yb, Tb, Sm and Nd in a total amount of “c” atomic % and at least one element selected from the group consisting of La, Ce, Pr, Eu and Mm in a total amount of “d” atomic %, wherein “c” and of “d” satisfy the following expressions (4) to (6):     0≦ c≦ 3.0;  (4) 0 ≦d≦ 2.0; and  (5) 0.1 ≦b+c+d≦ 6.0.  (6)   
   
   
       110 . The method of producing a high strength and high toughness metal according to  claim 59 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B and C in a total amount of larger than 0 atomic % to 2.5 atomic % or less.    
   
   
       111 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B and C in a total amount of larger than 0 atomic % to 2.5 atomic % or less.    
   
   
       112 . The method of producing a high strength and high toughness metal according to  claim 71 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B and C in a total amount of larger than 0 atomic % to 2.5 atomic % or less.    
   
   
       113 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B and C in a total amount of larger than 0 atomic % to 2.5 atomic % or less.    
   
   
       114 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, Band C in a total amount of larger than 0 atomic % to 2.5 atomic % or less.    
   
   
       115 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said step for preparing a magnesium alloy is a step for producing a magnesium alloy casting product which contains at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B and C in a total amount of larger than 0 atomic % to 2.5 atomic % or less.    
   
   
       116 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said step for subjecting a magnesium alloy to a heat treatment is a step for subjecting said magnesium alloy to a heat treatment at temperatures of 300° C. to 550° C. for 10 minutes or more to shorter than 24 hours.    
   
   
       117 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said step for subjecting a magnesium alloy to a heat treatment is a step for subjecting said magnesium alloy to a heat treatment at temperatures of 300° C. to 550° C. for 10 minutes or more to shorter than 24 hours.    
   
   
       118 . The method of producing a high strength and high toughness metal according to  claim 59 , 
 wherein said step for producing a magnesium alloy casting product comprises:    a step for refining a mineral ore containing rare-earth elements to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       119 . The method of producing a high strength and high toughness metal according to  claim 60 , 
 wherein said step for producing a magnesium alloy casting product comprises:    a step for refining a mineral ore containing rare-earth elements to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       120 . The method of producing a high strength and high toughness metal according to  claim 71 , 
 wherein said step for producing a magnesium alloy casting product comprises:    a step for refining a mineral ore containing rare-earth elements to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       121 . The method of producing a high strength and high toughness metal according to  claim 72 , 
 wherein said step for producing a magnesium alloy casting product comprises:    a step for refining a mineral ore containing rare-earth elements to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       122 . The method of producing a high strength and high toughness metal according to  claim 81 , 
 wherein said step for producing a magnesium alloy casting product comprises:    a step for refining a mineral ore containing rare-earth elements to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       123 . The method of producing a high strength and high toughness metal according to  claim 86 , 
 wherein said step for producing a magnesium alloy casting product comprises:    a step for refining a mineral ore containing rare-earth elements to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material for casting to produce said magnesium alloy which contains the rare-earth elements in a total amount of 6.0 atomic % or less.    
   
   
       124 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said magnesium alloy before subjecting to said plastic working has a grain size of 100 nm to 500 μm.    
   
   
       125 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said magnesium alloy before subjecting to said plastic working has a grain size of 100 nm to 500 μm.    
   
   
       126 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said magnesium alloy after subjecting to said plastic working has an hcp-Mg phase having a dislocation density one-digit larger than a long-period stacking ordered structure phase.    
   
   
       127 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said magnesium alloy after subjecting to said plastic working has an hcp-Mg phase having a dislocation density one-digit larger than a long-period stacking ordered structure phase.    
   
   
       128 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said magnesium alloy is plastically worked at 250° C. or higher.    
   
   
       129 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said magnesium alloy is plastically worked at 250° C. or higher.    
   
   
       130 . The method of producing a high strength and high toughness metal according to  claim 57 , 
 wherein said plastic working is carried out by at least one process in rolling, extrusion, ECAE, drawing, forging, cyclic working of these workings and FSW.    
   
   
       131 . The method of producing a high strength and high toughness metal according to  claim 69 , 
 wherein said plastic working is carried out by at least one process in rolling, extrusion, ECAE, drawing, forging, cyclic working of these workings and FSW.    
   
   
       132 . A method of producing a high strength and high toughness metal, 
 wherein a mineral ore containing rare-earth elements is refined to prepare a rare-earth alloy containing plural rare-earth elements;    the rare-earth alloy is used as a part of starting material and made into liquid having a composition of general formula of Mg (100-x-y) Y x Zn y  (1<x<5, 0.3<y<6; x and y represent atomic %);    said liquid is rapidly solidified into powder, thin band or thin wire; and    said powder, thin band or thin wire is solidified so as to be applied with shear.    
   
   
       133 . The method of producing a high strength and high toughness metal according to  claim 118 , 
 wherein said rare-earth alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of 50 atomic % or more and at least one rare-earth element other than Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of less than 50 atomic %.    
   
   
       134 . The method of producing a high strength and high toughness metal according to  claim 132 , 
 wherein said rare-earth alloy contains at least one element selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of 50 atomic % or more and at least one rare-earth element other than Y, Gd, Tb, Dy, Ho, Er, Tm and Lu in a total amount of less than 50 atomic %.    
   
   
       135 . The high strength and high toughness metal according to any one of claims  1 ,  2 ,  4  and  5 , 
 wherein said long-period stacking ordered structure phase has a density modulation.