(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: 采用铜模喷铸与高温退火相结合，研究快冷AZ91+SiC合金组织细化与高温晶粒长大，揭示SiC颗粒对亚快速凝固镁合金异质形核及热稳定性的影响。结果表明：SiC可促进亚快速凝固过程中异质形核，阻碍凝固界面迁移，显著细化喷铸合金组织。400 ℃等温退火后，组织从枝晶向等轴晶转变并发生明显晶粒长大，快冷AZ91合金保温8 h后平均晶粒尺寸达78 μm。添加2%SiC后，晶粒长大得到有效控制，8 h退火处理后平均晶粒尺寸仅为22 μm。SiC的存在提高了基体中晶格畸变，退火组织中析出层片状与粒状共存的沉淀相。晶粒细化及SiC的添加提高了快冷镁合金显微硬度。随退火时间延长，合金硬度下降。沉淀相的析出导致AZ91+2%SiC合金硬度增加，最高可达111HV，比AZ91合金的硬度提高63.2%。
关键字: 镁合金；凝固；冷却速率；异质形核；晶粒长大
（National Defense Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China）
Abstract:Using copper-mould spray casting and annealing techniques, microstructure refinement and grain growth at high temperature for quenched AZ91+SiC alloy were analyzed. Effects of SiC on heterogeneous nucleation of sub-rapid solidified alloy and thermal stability were elucidated. Results show that SiC promotes heterogeneous nucleation and inhibits interface migration. Grain size in spray casted alloy reveals significant reduction. After annealing at 400 ℃, dendrite transits to equiaxed grain, accompanied by obvious grain growth. The grain size of quenched AZ91 alloy after annealing for 8 h is 78 μm, whereas it reduces to 22 μm after adding 2%SiC, indicating the suppression of grain growth. The increase of lattice distortion by SiC generates lamellar and granular precipitations. Grain refinement and SiC increase the micro-hardness of quenched alloy and reduction occurs for longer annealing time. The maximum hardness of 111HV can be obtained in AZ91+2%SiC alloy due to precipitates, which increases by 63.2% than that of AZ91 alloy.
Key words: magnesium alloy; solidification; cooling rate; heterogeneous nucleation; grain growth
