High-strength magnesium alloy wire rod, production method therefor, high-strength magnesium alloy part, and high-strength magnesium alloy spring

Abstract

A high-strength magnesium alloy wire rod suitable for products in which at least one of bending stress and twisting stress primarily acts is provided. The wire rod has required elongation and 0.2% proof stress, whereby strength and formability are superior, and has higher strength in the vicinity of the surface. In the wire rod, the surface portion has the highest hardness in a cross section of the wire rod, the highest hardness is 170 HV or more, and the inner portion has a 0.2% proof stress of 550 MPa or more and an elongation of 5% or more.

1 . A high-strength magnesium alloy wire rod used for members in which at least one of bending stress and twisting stress primarily acts, the wire rod comprising:
 a surface portion having the highest hardness in a cross section of the wire rod, the highest hardness being 170 HV or more;   an inner portion having a 0.2% proof stress of 550 MPa or more and an elongation of 5% or more.   
     
     
         2 . The high-strength magnesium alloy wire rod according to  claim 1 , wherein
 the magnesium contains Mg as a main element and Ni and Y.   
     
     
         3 . The high-strength magnesium alloy wire rod according to  claim 2 , wherein
 the magnesium consists of 2 to 5 atomic % of Ni, 2 to 5 atomic % of Y, and the balance of Mg and inevitable impurities.   
     
     
         4 . The high-strength magnesium alloy wire rod according to  claim 1 , wherein the portion having the highest hardness in the vicinity of the surface has an average grain diameter of 1 μm measured by an EBSD method. 
     
     
         5 . A production method for a high-strength magnesium alloy wire rod, the method comprising:
 a step for yielding a raw material in a form of foil strips, foil pieces, or fibers of a magnesium alloy by a rapid solidification method,   a sintering step for forming a billet by bonding, compressing, and sintering the raw material,   a step for plastic forming the billet, thereby obtaining the wire rod according to  claim 1 .   
     
     
         6 . A production method for a high-strength magnesium alloy wire rod, the method comprising:
 a step for forming fibers by a molten metal extraction method,   a sintering step for forming a billet by bonding, compressing, and sintering the fibers,   an extruding step for directly charging the billet into a container of a press machine and extruding the billet, thereby obtaining the wire rod according to  claim 1 .   
     
     
         7 . The production method for a high-strength magnesium alloy wire according to  claim 5 , wherein
 the sintering step is performed in a temperature of 350 to 500° C. for 10 minutes or more at a pressure of 25 MPa or more.   
     
     
         8 . The production method for a high-strength magnesium alloy wire according to  claim 6 , wherein
 the extruding step is performed in a temperature of 315 to 335° C. at an extruding rate of 5 to 13 with a speed of 2.5 mm/second or less of a press ram.   
     
     
         9 . A high-strength magnesium alloy part produced from the high-strength magnesium alloy wire according to  claim 1 . 
     
     
         10 . A high-strength magnesium alloy spring produced from the high-strength magnesium alloy wire according to  claim 1 . 
     
     
         11 . The production method for a high-strength magnesium alloy wire according to  claim 6 , wherein
 the sintering step is performed in a temperature of 350 to 500° C. for 10 minutes or more at a pressure of 25 MPa or more.