(南昌航空大学 轻合金加工科学与技术国防重点学科实验室，南昌 330063)
摘 要: 采用铜模喷铸与等温热处理相结合，制备出纳米SiC参与下快冷镁合金细晶组织，研究热处理温度对非平衡凝固镁合金固溶组织转变的影响及其高温晶粒长大行为。结果表明：提高冷速与添加纳米SiC可实现镁合金的复合细化，有利于形成细小花瓣状组织。经320、370和400 ℃等温处理2 h后，快冷AZ91+2%纳米SiC合金从不完全固溶向完全固溶发生转变，溶质偏析程度降低，同时，晶界β-Mg17Al12相不断消失，最终获得多边形等轴晶组织。由于纳米SiC对晶界迁移起到良好的抑制作用，亚稳细晶组织的高温晶粒长大行为得到有效控制，其中经400 ℃固溶8 h后的平均晶粒尺寸仅为13 μm，快冷合金的热稳定性得到显著提高。
关键字: 镁合金；非平衡凝固；固溶处理；组织细化；晶粒长大
（National Defence Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China）
Abstract:With the combination of copper mould spray casting and isothermal heat treatment, rapidly cooled magnesium alloy with fine grain microstructure was prepared by adding nano SiC. The effects of annealing temperature on solid solution transition and high temperature grain growth behavior were elucidated. The results show that both the increase of cooling rate and the addition of SiC promote duplex refinement of magnesium alloy, which is beneficial to the formation of fine petal-like structure. After isothermal treatment at 320, 370 and 400 ℃ for 2 h, a transition from insufficient solid solution to complete solid solution occurs, accompanied by the reduction of solute segregation. The disappearance of β-Mg17Al12 in grain boundary generates the formation of polygon equiaxed grain structure. Due to the excellent inhibition effect of nano SiC on grain boundary migration, the grain growth at high temperature is effectively suppressed. The average grain size of rapidly cooled alloy after solid solution at 400 ℃ for 8 h is merely 13 μm, and the thermal stability of fine grain microstructure is greatly improved.
Key words: magnesium alloy; non-equilibrium solidification; solid solution treatment; microstructure refinement; grain growth
