Magnesium base alloy pipes and method of manufacturing the same

Abstract

A magnesium base alloy pipe having high strength and toughness is provided along with a method of manufacturing such pipes. A magnesium base alloy pipe, wherein the pipe is produced by drawing a pipe blank of a magnesium base alloy comprising containing either of the following ingredients (1) or (2): (1) about 0.1-12.0 mass % of Al; or (2) about 1.0-10.0 mass % of Zn and about 0.1-2.0 mass % of Zr. The novel alloy pipe is manufactured by a method comprising steps of providing the above-described pipe blank, pointing the pipe blank, and drawing the pointed pipe blank. The drawing step is executed at a drawing temperature above approx. 50° C.

1 . A magnesium base alloy pipe characterized in that the pipe is produced by drawing a pipe blank of a magnesium base alloy, the pipe has a 0.75 or greater YP ratio,
 wherein the pipe contains either of the following ingredients compositions (1) or (2):
 (1) 0.1-12.0 mass % of Al; or 
 (2) 1.0-10.0 mass % of Zn and 0.1-2.0 mass % of Zr; and 
   a tensile strength of the pipe is 250 MPa or above.   
   
   
       2 . The magnesium base alloy pipe according to  claim 1  above, wherein said pipe has a 3% or higher. 
   
   
       3 . The magnesium base alloy pipe according to  claim 2 , wherein said tensile strength is 350 MPa or above. 
   
   
       4 . The magnesium base alloy pipe according to  claim 2 , wherein said elongation is in the range of 15-20% and said tensile strength is in the range of 250-350 MPa. 
   
   
       5 . The magnesium base alloy pipe according to  claim 2 , wherein said elongation is 5% or above and said tensile strength is 280 MPa or above. 
   
   
       6 . The magnesium base alloy pipe according to  claim 5 , wherein said tensile strength is above 300 MPa. 
   
   
       7 . The magnesium base alloy pipe according to  claim 5 , wherein said elongation is 5% or above but below 12%. 
   
   
       8 . The magnesium base alloy pipe according to  claim 5 , wherein said elongation is 12% or above. 
   
   
       9 . (canceled) 
   
   
       10 . The magnesium base alloy pipe according to  claim 1 , wherein said YP ratio is 0.75 or above but below 0.90. 
   
   
       11 . The magnesium base alloy pipe according to  claim 1 , wherein said YP ratio is 0.90 or above. 
   
   
       12 . The magnesium base alloy pipe according to  claim 1 , wherein said pipe has a 0.2% proof stress of 220 MPa or above. 
   
   
       13 . The magnesium base alloy pipe according to  claim 12 , wherein said 0.2% proof stress is 250 MPa or above. 
   
   
       14 . The magnesium base alloy pipe according to  claim 1 , wherein said alloy has a 10 μm or smaller average grain size. 
   
   
       15 . The magnesium base alloy pipe according to  claim 1 , wherein said alloy has a duplex grain structure comprising fine grains and coarse grains. 
   
   
       16 . The magnesium base alloy pipe according to  claim 15 , wherein said alloy has a duplex grain structure comprising grains having a 3 μm or smaller average grain size and grains having a 15 μm or greater average grain size. 
   
   
       17 . The magnesium base alloy pipe according to  claim 16 , wherein said grains having a 3 μm smaller average grain size have a 10% or greater grains area share. 
   
   
       18 . The magnesium base alloy pipe according to  claim 1 , wherein said alloy has a mixed structure comprising twins and recrystallized grains. 
   
   
       19 . The magnesium base alloy pipe according to any one of the preceding  claims 1  through  8  and  10  through  18 , wherein said pipe has a surface roughness Rz defined by Rz≦5 μm on the surface thereof. 
   
   
       20 . The magnesium base alloy pipe according to any one of the preceding  claims 1  through  8  and  10  through  18 , wherein said pipe has a 80 MPa or smaller axial residual tensile stress in the surface thereof. 
   
   
       21 . The magnesium base alloy pipe according to any one of the preceding  claims 1  through  8  and  10  through  18 , wherein said pipe has a 0.02 mm or smaller differential outside diameter. 
   
   
       22 . The magnesium base alloy pipe according to any one of the preceding  claims 1  through  8  and  10  through  18 , wherein said pipe has a noncircular cross-sectional shape. 
   
   
       23 . The magnesium base alloy pipe according to any one of the preceding  claims 1  through  8  and  10  through  18 , wherein said alloy comprises 0.1-12.0 mass % of Al plus 0.1-2.0 mass % of Mn. 
   
   
       24 . The magnesium base alloy pipe according to  claim 23 , wherein said alloy comprises 0.1-12.0 mass % of Al plus at least one ingredient to be selected from the group consisting of 0.1-5.0 mass % of Zn and 0.1-5.0 mass % of Si. 
   
   
       25 . The magnesium base alloy pipe according to any one of the preceding  claims 1  through  8  and  10  through  18 , wherein said pipe have a 0.5 mm or smaller wall thickness. 
   
   
       26 . The magnesium base alloy pipe according to any one of the preceding  claims 1  through  8  and  10  through  18 , wherein said pipe comprise a butted pipe having longitudinally a uniform outside diameter with its inside diameters at its opposite end portions being smaller than that of its intermediate portion. 
   
   
       27 . A method of manufacturing a magnesium base alloy pipe comprising:
 a step of providing a pipe blank of any one of the following magnesium base alloys (A) through (C):
 (A) a magnesium base alloy containing 0.1-2.0 mass % of Al; 
 (B) a magnesium base alloy containing 0.1-12.0 mass % of Al plus at least one ingredient to be selected from the group consisting of 0.1-2.0 mass % of Mn, 0.1-5.0 mass % of Zn and 0.1-5.0 mass % of Si; or 
 (C) a magnesium base alloy containing 1.0-10.0 mass % of Zn and 0.1-2.0 mass % of Zr; 
   a metal pointing step for pointing said pipe blank; and   a drawing step for drawing the resultant pointed pipe blank;   wherein said drawing step is executed at a drawing temperature of 50° C. or above.   
   
   
       28 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein heating to said drawing temperature is accomplished by heating the pipe blank in an atmosphere furnace, heating the same in a high-frequency heating furnace, or heating a drawing die. 
   
   
       29 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein said drawing temperature ranges from 100° C. to 350° C. 
   
   
       30 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein area reduction ratio in one drawing pass is 5% or above. 
   
   
       31 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein said drawing step is accomplished in a multistep process using plurality of dies. 
   
   
       32 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein said drawing step is accomplished by using at least a die, heating only an initial working portion of a pointed pipe blank where it contacts said die, and drawing said pointed pipe blank at the temperature of the thus heated initial working portion or as it cools naturally therefrom. 
   
   
       33 . The method of manufacturing a magnesium base alloy pipe according to  claim 32 , wherein a heating temperature of said initial working portion ranges of 150° C. or more but below 400° C. 
   
   
       34 . A method of manufacturing a magnesium base alloy pipe comprising:
 a step of providing a pipe blank of any one of the following magnesium base alloys (A) through (C):
 (A) a magnesium base alloy containing 0.1-12.0 mass % of Al; 
 (B) a magnesium base alloy containing 0.1-12.0 mass % of Al plus at least one ingredient to be selected from the group consisting of 0.1-2.0 mass % of Mn, 0.1-5.0 mass % of Zn and 0.1-5.0 mass % of Si; or 
 (C) a magnesium base alloy containing 1.0-10.0 mass % of Zn and 0.1-2.0 mass % of Zr;
 a metal pointing step for pointing said pipe blank; and 
 a drawing step for drawing the resultant pointed pipe blank; 
 wherein said pointing step is accomplished by heating at least a front working end of the pipe blank entering a pointing machine. 
 
   
   
   
       35 . The method of manufacturing a magnesium base alloy pipe according to  claim 34 , wherein said front working end is heated at its portion contacting said pointing machine. 
   
   
       36 . The method of manufacturing a magnesium base alloy pipe according to  claim 34 , wherein said pointing step is executed by controlling at least the temperature of said front working end entering said pointing machine to 50-450° C. 
   
   
       37 . The method of manufacturing a magnesium base alloy pipe according to  claim 34 , wherein said pointing step is executed with a heat insulating material inserted in the front end of the pipe blank. 
   
   
       38 . The method of manufacturing a magnesium base alloy pipe according to  claim 34 , wherein said pointing step is executed on a swaging machine by heating the front end of the pipe blank in a heated liquid. 
   
   
       39 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , further comprising a lubrication step for lubricating at least an initial working portion of the pipe blank in advance of said drawing step. 
   
   
       40 . The method of manufacturing a magnesium base alloy pipe according to  claim 39 , wherein said lubrication step comprises immersing the pipe blank in a preheated lubricant. 
   
   
       41 . The method of manufacturing a magnesium base alloy pipe according to  claim 39 , wherein said lubrication step forms a lubricant coating on the pipe blank. 
   
   
       42 . The method of manufacturing a magnesium base alloy pipe according to  claim 41 , wherein said lubricant coating comprises a fluorine-based resin. 
   
   
       43 . The method of manufacturing a magnesium base alloy pipe according to  claim 42 , wherein said fluorine-based resin comprises a PTFE or PFA. 
   
   
       44 . The method of manufacturing a magnesium base alloy pipe according to  claim 41 , wherein said lubricant coating is formed by dispersing a fluorine-based resin in water to prepare an aqueous dispersion thereof, immersing the pipe blank in said aqueous dispersion, and heating the pipe blank taken out of said aqueous dispersion. 
   
   
       45 . The method of manufacturing a magnesium base alloy pipe according to  claim 44 , wherein the pipe blank taken out of said aqueous dispersion at about 300-450° C. 
   
   
       46 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein said drawing step comprises mandrel drawing using a mandrel passing through a die and a lubricant coating is formed on said mandrel. 
   
   
       47 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein said drawing step comprises:
 a first plain drawing step in which one end of the pipe blank is passed through a die inside and the pipe blank is drawn without squeezing its wall between the inside of the die and a plug;   a plug drawing step for squeezing an intermediate portion of the pipe blank between the inside of the die and the plug; and   a second plain drawing step in which the other end of the pipe blank is drawn without squeezing its wall between the inside of the die and the plug;   to form a butted pipe having thick-walled opposite ends and a thin-walled intermediate portion.   
   
   
       48 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , wherein said drawing step comprises mandrel drawing using a mandrel having longitudinally varied outside diameters to form a butted pipe. 
   
   
       49 . The method of manufacturing a magnesium base alloy pipe according to  claim 48 , wherein the pipe blank is drawn by grasping its front working end extending out of a die exit. 
   
   
       50 . The method of manufacturing a magnesium base alloy pipe according to  claim 48 , wherein said drawing step is executed in multiple passes by using dies having varied inside diameters. 
   
   
       51 . The method of manufacturing a magnesium base alloy pipe according to  claim 27 , further comprising a heat treatment step for heating a drawn pipe at 150° C. or higher temperatures. 
   
   
       52 . The method of manufacturing a magnesium base alloy pipe according to  claim 51 , wherein said heat treatment step is executed at 300° C. or lower temperatures.