热压制工艺回收AZ91D镁合金屑的半固态组织演变

摘要

AZ91D magnesium alloy chips,which were directly collected on the spot of machining process,were recycled to prepare billet via hot pressing for semi-solid processing.The semi-solid microstructure evolution of the billet during reheating was investigated.The results indicate that there are three stages during reheating to semi-solid state: the dissolution of Mgl7Al12 and diffusion of AI into α-Mg matrix,the melting of the region with high content of solute and formation of isolated solid particles,and spheroidization and growth of solid particles.Meanwhile,a number of entrapped liquid droplets form within solid particles.In addition,the number and size of entrapped liquid droplets rely on the holding time in the semi-solid temperature range.With increasing isothermal holding time,the solid fraction remains unchanged when the solid-liquid system reaches the dynamic equilibrium at last,while the solid particles become more globular and the average size of solid particles increases owing to the decreasing of interracial energy and the effect of interfacial tension.%以从机械加工现场直接收集的AZ91D镁合金屑料为原料,采用热压制工艺再生制备半固态加工所需的坯料,研究二次加热过程中的半固态组织演变.结果表明,半固态组织演变可分为三个阶段:Mg17Al12相的溶解和Al原子的扩散,高溶质含量区域的熔化和固相颗粒的生成,固相颗粒的球化和长大.同时,在固相颗粒内部形成大量的嵌入式液滴.这种嵌入式液滴的数量和尺寸随着保温时间的变化而变化.随着保温时间的延长,固、液两相最终达到动态平衡,固相率不再发生变化.由于界面能降低和界面张力的作用使固相颗粒尺寸逐渐增大,并且越来越圆整.