Microstructure Evolution And Properties Of Mg-4Y-3Nd-xDy-0.5Zr In As-cast And Heat Treatment

WE43alloy of Mg-Y-Nd system alloys has been widely applied in aerospace,aviation, automotive and other fields in foreign countries because of its excellentmechanical properties at room temperature, stable high-temperature mechanicalproperties and corrosion resistance. Excellent high temperature mechanicalproperties of WE43alloy could be obtained after T6(solution+artificia l aging)treatment. This paper studies solution treatment of Mg-4Y-3Nd-xDy-0.5Zr (x=2,3,5)alloy, which is obtained by adding Dy elements to the system of WE43alloy.Composition and distribution of phases after different solution treatment, theinfluence law of grain growth are analyzed and the influence of aging treatment onhigh temperature mechanical properties are analyzed.The solution treatment to Mg-4Y-3Nd-xDy-0.5Zr (x=2,3,5) alloy were carriedat different temperature. Solution treated at500℃, the bone-like alloy graduallyreduce，the massive areal density is gradually increasing. Solution under theconditions of525℃, with the extension of the solution time, the alloy in thebone-like gradual reduction, Mg-4Y-3Nd-xDy-0.5Zr (x=3,5) the surface density ofthe alloy blockthe gradual increase of Mg-4Y-3Nd-2Dy-0.5Zr massive phase densityfirst increases and then decreases. Solut ion under the conditions of550℃, with theextension of the solution time, the alloy in the bone-like rapid disappearance of theblock relative to the surface density decreases sharply.The rate of grain increase in solution of Mg-4Y-3Nd-2Dy-0.5Zr alloydecreases with the increase of solution time treated at500℃and525℃.In theinitial stage of solution treatment,the grain size increase modle mainly is internalgrain boundary disappeatance of several adjacen grain with similar crystalorientation.while, the grain size increase modle changed from disappeatance ofinternal grain boundary to moving of grain boundary to incre ase grain size for thedecrease of pinning effect of phases on grain boundaries with phases decrease afterlong solution time. However, with the increase of solution time treated at550℃,therate of grain increase in solution of Mg-4Y-3Nd-2Dy-0.5Zr alloy increases,for rapiadecrease of pinning effect on grain boundary with rapid phases decrease. After thesame solution treatment, grain size decreased with the increasr of Dy content in thealloy,suggesting the dominant pinning effect of phases on incease of grain size too.After different solution and aging treatment of Mg-4Y-3Nd-3Dy-0.5Zr alloy at225℃for12h, the tensile mechanical properties at250℃after solution treatment at525℃for8h is highest, reachig302MPa,which is about21%higher than of WE43 alloy that after T6treatment. to improve by to525℃solid solution40h alloy, thehighest elongation of17.7%for the WE43alloy after T6treatment4-6times. Withthe increase of solution temperature and solution time, the fracture mode of alloychanged from fracture toughness by porous gathering to brittle cleavage fracture andfrom transgranular fracture to intergranular fracture.Rectangular phases influences inprove Mechanical properties，but the ductilitydecrease and the yield strength increased with the decrease of surface density.