深冷处理对非平衡凝固Mg-6Al-1Y合金组织的影响

Influences of Cryogenics Treatment on the Non-equilibrium Solidified Mg-6Al-1Y Alloy

采用铜模喷铸与深冷处理相结合,制备出Mg-6Al-1Y细晶合金,对比研究深冷处理对合金快冷组织及其时效析出的影响。结果表明,由于凝固过冷度及形核率增大,快冷Mg-6Al-1Y合金的组织主要为细小等轴枝晶,局部存在微米级粒状晶,同时形成高固溶组织及位错结构。深冷过程中引起的应力累积效应有利于快冷合金中细小枝晶发生碎断,并随深冷时间的增加而趋于球化,其中深冷32 h后的平均晶粒尺寸降至10μm,同时位错密度急剧升高。经200℃×16 h时效处理后,快冷与深冷协同作用下Mg-6Al-1Y合金的晶界不连续析出程度大幅增加,同时晶内连续析出相形貌及数量得到有效改善,合金显微硬度(HV)高达71.3,相比原始快冷合金提高了11.9%。

Grain refinement of Mg-6 Al-1 Y alloy was achieved by the collaboration of copper mold injection casting and cryogenics treatment. The influences of cryogenics treatment on non-equilibrium solidified structure and subsequent precipitation behavior were investigated. The results reveal that with the increase of undercooling and corresponding nucleation rate, the formation of fine equiaxed dendrite grains with partial micron-size granular grains can be observed, accompanied by the formations of high supersaturated structure and considerable dislocation defect under the non-equilibrium solidification condition. Stress accumulation induced by cryogenic treatment is beneficial to the fragmentation of fine dendrites in rapidly cooled alloy and spheroidization of segments occurs subsequently. The average grain size is decreased to 10 μm and the amount of dislocation density is increased significantly after cryogenics for 32 h. As for the rapid cooled and cryogenic treated alloy, discontinuous precipitation at grain boundary is accelerated during the isothermal annealing at 200 ℃ for 16 h. Moreover, both the morphology and quantity of continuous precipitation within grain are improved effectively. The resultant hardness is increased to 71.3 HV, which is 11.9% higher than that of the original rapidly cooled alloy.