A2017半固态合金二次加热组织演化

对SCR技术制备的A2017半固态坯料进行二次加热,利用光学显微镜,电镜,图像分析仪等手段,对坯料二次加热微观组织的演化进行了研究·实验结果表明,在相同加热温度条件下,随着保温时间的延长,晶粒平均等积圆直径增大,晶粒越来越圆整,液相率增加;提高二次加热温度,晶粒长大和球化速度加快·二次加热最佳工艺条件为加热温度580℃,保温时间40～60min或者加热温度600℃,保温20～40min,晶粒平均等积圆直径为70～90μm,固相率在70%左右,适合于半固态加工·组织演化机制分析表明,加热初期阶段,液相少,晶粒主要通过碰撞熔合快速长大;随着保温时间延长,液相增加,晶粒主要通过原子扩散慢速长大并发生...

Microstructures Evolution of the Semi-solid A2017 Alloy During Reheating

The semi-solid A2017 alloys provided with shearing/cooling roll (SCR) technology were reheated, and its microstructural evolution was studied by means of optical microscope, SEM and graphical analyzer. The results indicated that the mean diameter of grains increases, volume fraction of liquid increases and getting spheriform grains with the prolongation of isothermal holding time. In addition, the grains grow up and are sphericized faster with the reheating temperature rising. The group of reheating process parameters is reheating temperature 580°C/holding time 40-60 min or 600°C/20-40 min with mean diameter of grains 70-90 μm and the got volume fraction of solid is 70%. Such a temperature/time group is suitable for thixo-forming. Based on the experimental results, the microstructural evolution mechanism of the semi-solid A2017 alloy reheated in semi-solid state was analyzed. It is found that in the early stage of the whole reheating process, the volume fraction of liquid is low and grains grow up fast mainly through crashing and fusing, while grains grow up slowly and are sphericized mainly through elements diffusion with increasing volume fraction of liquid as the temperature holding time prolonged.