铜模喷铸Mg-6Al-1Y合金快冷组织形成及其固溶行为

Quenched Microstructure of Spray-casted Mg-6Al-1Y Alloy and Its Solid Solution Behavior

采用真空感应熔炼与等温固溶相结合,研究了稀土Y对铜模喷铸Mg-6Al合金快冷组织形成及其热稳定性的影响。结果表明:非平衡凝固Mg-6Al-1Y合金中形成亚稳稀土Mg 24 Y 5相,能够促进晶粒细化,抑制溶质偏析,形成细小球状晶组织。随铜模内径降低,凝固冷速增加,晶粒细化效果更加显著,其中内径为2 mm时所获得的平均晶粒尺寸减小到2μm以内。Y的加入导致晶界处β相转变温度由425.57℃升高到429.46℃,提高了快冷Mg-6Al合金的高温热稳定性。高冷速引起的细晶强化有利于增加快冷Mg-6Al-1Y合金的显微硬度。经400℃/2 h固溶处理后β相的溶解导致快冷合金硬度下降。

Effects of rare earth Y on quenched microstructure of spray-casted Mg-6Al alloy and its thermal stability behavior were investigated by vacuum induction melting and isothermal solid solution treatment.The results show that meta-stable Mg 24 Y 5 forms during the non-equilibrium solidification of Mg-6Al-1Y,which promotes the grain refinement and suppresses the solute segregation.Consequently,the microstructure with fine spherical grain can be obtained.Cooling rate is increased with decreasing the inner diameter of copper mould.As a result,grain refinement is strengthened and the mean grain size is less than 2μm as for inner diameter of 2 mm.The addition of Y improves the transformation temperature of grain boundaryβphase from 425.57℃to 429.46℃,which is beneficial to the thermal stability of quenched Mg-6Al alloy.The strengthening effect ascribed to grain refinement with high cooling rate favors the increase of micro-hardness of quenched Mg-6Al-1Y.The subsequent solid solution treatment with 400℃/2 h reduces its hardness value due to the dissolution ofβphase.