High-Strength and High-Toughness magnesium Based Alloy, Driving System Part Using the Same and Manufacturing Method of High-Strength and High-Toughness magnesium Based Alloy Material

Abstract

A high-strength and high-toughness magnesium based alloy contains, by weight, 1 to 8% rare earth element and 1 to 6% calcium and the maximum crystal grain diameter of magnesium constituting a matrix is not more than 30 μm. At least one intermetallic compound ( 6 ) of rare earth element and calcium has a maximum grain diameter of 20 μm or less and it is dispersed in a crystal grain boundary ( 5 ) and a crystal grain ( 4 ) of magnesium of the matrix.

1 . A high-strength and high-toughness magnesium based alloy provided such that a plastic forming process is performed to magnesium based alloy powder containing, by weight, 1 to 8% rare earth element and 1 to 6% calcium to miniaturize a magnesium crystal grain that constitutes a matrix and a compound grain dispersed in the matrix, and immediately after heating a powder solidified body provided from the miniaturized magnesium based alloy powder, a warm extrusion process is performed to it, characterized in that the maximum crystal grain diameter of magnesium that constitutes the matrix is not more than 30 μm, 
 said magnesium based alloy contains at least one intermetallic compound of said rare earth element and said calcium, and    when it is assumed that the maximum grain diameter of said intermetallic compound is “D” and the minimum grain diameter thereof is “d”, D/d≦5 is satisfied.    
   
   
       2 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , wherein the maximum grain diameter of the intermetallic compound is not more than 20 μm.  
   
   
       3 . The high-strength and high-toughness magnesium based alloy according to  claim 2 , wherein said intermetallic compound is a compound of aluminum and rare earth element.  
   
   
       4 . The high-strength and high-toughness magnesium based alloy according to  claim 2 , wherein said intermetallic compound is a compound of aluminum and calcium.  
   
   
       5 . (canceled)  
   
   
       6 . The high-strength and high-toughness magnesium based alloy according to  claim 2 , wherein said intermetallic compound is dispersed in said crystal grain boundary and crystal grain of magnesium that constitutes said matrix.  
   
   
       7 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , wherein the maximum crystal grain diameter of magnesium that constitutes the matrix is not more than 20 μm.  
   
   
       8 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , wherein the maximum crystal grain diameter of magnesium that constitutes the matrix is not more than 10 μm.  
   
   
       9 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , containing at least one kind, of element selected from a element group consisting of, by weight, 0.5 to 6% Zinc, 2 to 15% aluminum, 0.5 to 4% manganese, 1 to 8% silicon and 0.5 to 2% of silver.  
   
   
       10 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , wherein a tensile strength (σ) is not less than 350 MPa and a breaking extension (ε) is not less than 5%.  
   
   
       11 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , wherein the product of the tensile strength (σ) and the breaking extension (ε) is such that σ×ε≧4000 MPa·%.  
   
   
       12 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , wherein said rare earth element contains at least one kind of element selected from a group consisting of cerium (Ce), lanthanum (La), yttrium (Y), ytterbium (Yb), gadolinium (Gd), terbium (Tb), scandium (Sc), samarium (Sm), praseodymium (Pr), and neodymium (Nd).  
   
   
       13 . The high-strength and high-toughness magnesium based alloy according to  claim 1 , containing, by weight, 1.5 to 4% manganese, 2 to 15% aluminum and iron of 10 ppm or less, wherein the maximum grain diameter of an Al—Mn compound is not less than 20 μm.  
   
   
       14 . A driving system part for a car or a two-wheeled motor vehicle using the high-strength and high-toughness magnesium based alloy according to  claim 1 .  
   
   
       15 . A manufacturing method of a high-strength and high-toughness magnesium based alloy material comprising: 
 a step of miniaturizing a magnesium crystal grain that constitutes a matrix and miniaturizing a compound grain dispersed in the matrix by performing a plastic forming process to magnesium based alloy powder containing, by weight, 1 to 8% rare earth element and 1 to 6% calcium;    a step of manufacturing a powder solidified body from said miniaturized magnesium based alloy powder by compression molding; and    a step of providing an alloy material by heating said powder solidified body and immediately performing a warm extrusion process to it.