The Research On Refinement Of Semi-solid Forming Mg-20Al-0.8Zn Magnesium Alloy

Mg-20Al-0.8Zn is developed on the basis of it,which is study on the evolution mechanism of semi-solid isothermal heat treatment of AZ91D magnesium alloy.Early studies have shown that Mg-20A1-0.8Zn magnesium alloy have good characteristics of semi-solid.In order to improve the rheologic of semi-solid alloy,refinement method was selected.Chose Sb as modificator,optimized processing parameter of Sb refine Mg-20Al-0.8Zn magnesium alloy, and analyzed the effects of Sb modification on semi-solid microstructure of Mg-20Al-0.8Zn magnesium alloy in semi-solid isothermal heat treatment.The experimental results show that,the effects of Sb modification on microstructure of Mg-20Al-0.8Zn magnesium alloy is obviously with Sb content of 0.75%,metamorphic temperature is 780℃and pouring temperature is 700℃,and the size of Primary crystal is 85 (am.This is mainly because the melt product Mg₃Sb₂ phase after Sb added.This phase provide the core of the heterogeneous nucleation for Mg-20Al-0.8Zn magnesium alloy,increased the nucleation rate of alloy,and gathered at the solid/liquid interface front to resist grain growth, further refine the grains.Comparative Studied on the semi-solid isothermal heat treatment process of modification on Mg-20Al-0.8Zn magnesium alloy before and after.The temperature of the semi-solid isothermal heat treatment is 485℃,the time of obtain globular organization from 120min reduced to 30min after modification,the size of globular organization in semi-solid magnesium alloy from 103um reduced to 59um after modification,the continuance of globular organization increased to 75min after modification.It also because of Mg3Sb2 gathered at the solid/liquid interface front to resist grain growth.In order to adapt the die-cast adjust the ingot of die-cast with the semi-solid isothermal heat treatment process,take two-step heating method for it,that is first at 535℃for heat 30min,then cooled to 485℃for heat l00min.The results shown that can obtain the same effect of the semi-solid.Comparative Studied on forming experiment of liquid and semi-solid die-cast of Mg-20Al-0.8Zn magnesium after 0.75%Sb modification.The experimental results show that tensile strength of liquid die-cast is 198MPa,the hardness is 114HBS;tensile strength of semi-solid die-cast is 176MPa,the hardness is 124HBS.Scan appearance of fracture show that they were all rock-candy structure.