High performance creep resistant magnesium alloys

Abstract

The invention provides a magnesium based alloy consisting of at least 94.8% magnesium, 2.5-4.6% neodymium, 0.05-0.40% yttrium, and 0.03-0.65% zirconium, exhibiting good castability, high strength, high corrosion resistance and high creep resistance even at high temperatures. The alloy is suitable for high pressure die casting, sand casting, investment casting, permanent mold casting, twin roll casting, or direct chill casting.

1 . A lightweight alloy for high-temperature applications, consisting of
 i) at least 94.8 wt % magnesium,   ii) 2.5 to 4.6 wt % neodymium,   iii) 0.05 to 0.40 wt % yttrium,   iv) 0.03 to 0.65 wt. % zirconium, and   v) incidental impurities.   
     
     
         2 . An alloy according to  claim 1 , further containing up to 0.02 wt % calcium. 
     
     
         3 . An alloy according to  claim 1 , comprising essentially no heavy rare earth (HRE) elements with the atomic number from 61 to 71. 
     
     
         4 . An alloy according to  claim 1 , comprising essentially no cerium, lanthanum, and praseodymium. 
     
     
         5 . An alloy according to  claim 1 , comprising essentially no zinc. 
     
     
         6 . An alloy according to  claim 1 , wherein the total content of Nd and Y is higher than 4.3 wt %. 
     
     
         7 . A lightweight alloy according to  claim 1 , for prolonged operation at a temperature of up to 200° C. 
     
     
         8 . An alloy according to  claim 1 , usable for a process selected from the group consisting of high pressure die casting (HPDC), sand casting, investment casting, and permanent mold casting. 
     
     
         9 . An alloy according to  claim 1 , usable for a process comprising either twin roll casting with subsequent rolling, or direct chill casting with subsequent forging, extrusion or rolling. 
     
     
         10 . A lightweight alloy for high-temperature applications according to  claim 8  usable for HPDC. 
     
     
         11 . An alloy according to  claim 10 , which contains 2.8 to 4.3 wt % Nd, 0.06 to 0.25 wt % Y, 0.05 to 0.4 wt % Zr, and 0.0 to 0.02 wt % Ca. 
     
     
         12 . An alloy according to  claim 10 , exhibiting a castability of at least 96%, when measured in relative units characterizing oxidation resistance, fluidity, and dies sticking. 
     
     
         13 . An alloy according to  claim 10 , exhibiting a tensile yield strength (TYS) at 200° C. of at least 153 MPa. 
     
     
         14 . An alloy according to  claim 10 , exhibiting a compression yield strength (CYS) at 200° C. of at least 152 MPa. 
     
     
         15 . An alloy according to  claim 10 , exhibiting a minimum creep rate (MCR) of not more than 1.5×10 −10 /s at 200° C. under stress of 100 MPa. 
     
     
         16 . An alloy according to  claim 10 , exhibiting a corrosion rate under GM 9540 of not more than 2.7 mpy. 
     
     
         17 . An article cast of an alloy according to  claim 10 , exhibiting a superior combination of strength and ductility after T5 treatment which includes direct aging at 150-250° C. for 1-10 h. 
     
     
         18 . An article according to  claim 17 , exhibiting a superior combination of strength and ductility after T5 treatment which includes direct aging at 175-225° C. for 1-6 h. 
     
     
         19 . An alloy according to  claim 8  suitable for sand casting, investment casting, permanent mold casting, and low pressure modifications thereof, containing 2.7 to 3.4 wt % Nd, 0.15 to 0.40 wt % Y, 0.3 to 0.6 wt % Zr, and 0.0 to 0.02 wt % Ca. 
     
     
         20 . An article cast of an alloy according to  claim 19 , exhibiting a superior combination of performance properties after full T6 heat treatment comprising solid solution heat treatment at 520-560° C. for 1 to 16 hrs, followed by cooling in a quenching medium and by subsequent aging at 200-270° C. for 1 to 16 h. 
     
     
         21 . An article according to  claim 20 , exhibiting a superior combination of performance properties after full T6 heat treatment comprising solid solution heat treatment at 535-545° C. for 3 to 5 hrs, followed by cooling in a quenching medium and by subsequent aging at 225-250° C. for 3 to 6 h. 
     
     
         22 . An alloy according to  claim 9 , suitable for forging, extrusion, and rolling, which contains 2.8 to 3.8 wt % Nd, 0.20 to 0.40 wt % Y, 0.35 to 0.60 wt % Zr, and 0.0-0.02 wt % Ca. 
     
     
         23 . An article cast of an alloy according to  claim 22 , exhibiting a superior combination of performance properties after T5 heat treatment comprising aging at 200-250° C. for 1 to 16 h.