过热温度和时间对Al-21%Si合金凝固组织的影响

Influence of overheating temperature and holding time on solidification microstructure of Al-21%Si alloy

将0.5 g初始铸态Al-21%Si合金真空封装于14 mm的石英管中,分别在750、800、850和900℃温度下重熔并保温不同时间后水冷,采用光学显微镜分析Al-21%Si合金凝固组织。结果表明:Al-21%Si合金在750～850℃重熔保温20 min后初晶硅比初始铸态合金中的更大,但随着重熔温度的升高,初晶硅的颗粒尺寸逐渐减小,900℃温度下重熔时效果最好;在750℃重熔后初晶硅反而变粗,保温时间对初晶硅颗粒的尺寸影响不明显;在相对较慢的石英管水冷条件下,Al-21%Si合金中的共晶硅比初始铸态组织中的共晶硅更加细小;在750～900℃温度范围内保温不同的时间后,初晶硅的颗粒尺寸基本在25～43μm范围内波动;在800、850和900℃保温时均出现了不同生长程度的五瓣星形初晶硅组织。

As-cast Al-21% alloy with the weight of 0.5 g was encapsulated into a 14 mm evacuated quartz tube,and then the quartz tubes were heated at 750,800,850 and 900 ℃ for different time.The solidification microstructure of the treated Al-21%Si alloy was analyzed by optical microscopy.The results show that when overheated at 750-850 ℃ for 20 min,the primary Si is larger than that in the as received alloy.But the size of primary Si in the Al-21%Si alloy gradually decreases with the increasing of temperature,and the solidified alloy with finest primary Si is achieved at 900 ℃.While overheated at 750 ℃,the primary Si grows bigger than that in the as received alloy,and the effect of holding time on the size of primary Si is quite little.The eutectic Si in the alloy becomes smaller than that in the as received alloy because of lower cooling velocity.Most of the primary Si is with the size of 25-43 μm after overheating at 750-900 ℃ for different holding time.Five petal star-shaped primary Si with different growth level is observed for the alloy after overheating at 800,850 and 900 ℃,respectively.