超声作用下半连铸7050铝合金的偏析行为及形成机制

来源期刊：中国有色金属学报2011年第2期

论文作者：黎正华 李晓谦 张明 许显华

文章页码：318 - 324

关键词：7050铝合金；半连铸；逆偏析；超声；空化；偏析比

Key words：7075 aluminum alloy; semi-continuous casting; inverse segregation; ultrasonic; cavitation; segregation ratio

摘    要：采用SPECTRO-MAXx立式直读光谱仪和Leica金相显微镜，研究超声功率对半连铸过程中7050铝合金微观组织及溶质Zn元素径向分布的作用规律。结果表明：在超声外场作用下铸锭组织明显细化，混晶减少，溶质Zn元素的径向逆偏析程度减弱，并随着超声功率的增加，晶粒细化程度及宏观偏析的弱化效果更好，溶质Zn元素的偏析比由未加超声时的1.190降低为240 W功率超声作用时的1.086；在超声外场调控下，铝合金熔体偏析弱化的主要原因是由于形核率增加，晶粒细化，两相区液固相相对运动速度减小；液穴变浅，由铸锭收缩导致的富集液相径向流动减弱，是径向偏析程度减弱的另一原因；在半连续铸造过程中，采用超声外场控制液相的流动是弱化铸锭径向宏观偏析的有效手段。

Abstract: The macro-distribution of solute elements Zn and microstructure for 7050 aluminum alloy by semi-continuous casting under the ultrasonic field were investigated by SPECTRO-MAXx and Leica optic microscopy. The results show that the microstructure refines, the duplex structure consisting of coarse-cell and fine-cell dendritic grains decreases, the inverse segregation grade of Zn decreases effectively. With the increase of the ultrasonic power, the microstructure becomes finer and more uniform, the distribution of solute elements is more harmonious, the segregation ratio of Zn through 240 W ultrasonic treatment decreases to 1.086 from 1.190 without ultrasonic. After being treated by ultrasonic field, the nucleation ratio of the Al melt increases, the microstructure refines, the relative velocities of the solid and liquid phases in mushy zone decreases, and the shrinkage-induced flow of the enriched solute decreases due to the sump height decreases, which suppresses macro-segregation in a great degree. The liquid phases flow controlled by ultrasonic field is an effective means to weaken the macro-segregation in semi-continuous casting.