Mg-6Zn-1．5Gd-0．4Zr合金的半固态等温热处理组织演变研究

Microstructural Evolution of Mg-6Zn-1.5Gd-0.4Zr Alloy During Semi-Solid Isothermal Heat Treatment

研究了砂型铸造Mg-6Zn-1.5Gd-0.4Zr镁合金在半固态等温热处理过程中的组织演变,研究了等温时间、等温温度对组织形态的影响,并对组织演变机理进行了简单探讨。研究结果表明:540℃等温过程中,晶界处的共晶组织先发生熔解;随着等温时间的加长,α相(Mg)熔化分离,并在等温处理过程中由块状向球状转变;25 min时,转变为粒径约40～60μm的均匀球状组织;等温时间过长时,球状晶粒发生合并长大;合金等温温度越高,组织的球化进程就越快,异形长大后,晶粒越粗大。

The microstructure of Mg-6Zn-1.5Gd-0.4Zr magnesium alloy during semi-solid isothermal heat treatment was studied, the effect of isothermal time and annealing temperature on the microstructure during semi-solid isothermal heat treatment was analyzed, and the microstructure evolution mechanism was also discussed. It was found that, during isothermal heat treatment at 540 ℃, the eutectic phases at the grain boundry were dissolved first, and with the time increasing, the primary c（-phases were remelt and separated into the small lump, then changed into spheroidal grains gradually. After treated for 25 min, the well-distributed spheroidal grains ranging from 40 IJm to 60 IJm were formed. When the isothermal time was excessive, the spheroidal grains would grow up. The higher the isothermal temperature was, the faster the grains spheroidized and the coarser the grains were.