【摘要】 对近液相线铸造AZ91D镁合金半固态坯料进行部分重熔,通过改变部分重熔时的加热温度和保温时间来研究其微观组织的演化规律.结果表明,适当控制加热温度和时间,坯料部分重熔时可获良好的触变结构,且坯料铸造时的高冷却速率因促进了坯料组织细化和蔷薇化而在部分重熔时加快固相颗粒球化进程并使球化效果改善;坯料在近液相线温度静置30 min用水冷铁模浇注时,在 575-580℃,保温15-30min可获得较理想的重熔结构;而用石墨模浇注时,则为580℃保温15-30 min.研究还表明,重熔组织演化过程分球化预备、固相颗粒细化和球化及固相颗粒长大3个阶段.该进程是溶质和空位扩散以及相界面张力共同作用的结果.其中,前者在初期、后者在中后期起支配作用.更多还原

【Abstract】 The microstructure evolution of AZ91D magnesium alloy SSM (semi-solid metal) ingots obtained by near-liquidus casting was investigated under altering partial remelting temperature and holding time. The results indicate that good thixotropic microstructure would be obtained by controlling remelting temperature and holding time suitably, and the spheroidizing process is accelerated and improved due to refining and rosettizing of ingot microstructure at higher cooling rate during casting. For the ingots cast at near-liquidus and stewing for 30 min, optimizing thixotropic microstructure could be obtained at 575-580 ℃ for 15-30 min as cast in water-cooled-iron mould, and 580 ℃ for 15-30 min in graphite mould. The process of microstructure evolution during remelting includes spheroidization preparation, grains refining and spheroidizing, and grains growth. The diffusion of solute and vacancy, and the boundary tension play a predominant role respectively at the primary stage, and the middle-final stage.更多还原