超声半连铸下7050合金大扁锭的微观组织及宏观偏析行为

在500mm×1320mm的7050铝合金扁锭铸造中引入超声外场,研究常规铸造与超声铸造下的微观组织形貌、分布和宏观偏析特征。结果表明,超声外场可以有效减小晶粒的尺寸、抑制组织中粗枝晶的产生并促进铸锭内组织的均匀分布;同时,加入超声场后,溶质元素Zn、Mg、Cu沿长度方向和宽度方向对称轴的偏析指数分别由0.1013、0.1117、0.1260和0.1119、0.1113、0.1281减小到0.0835、0.0790、0.1027和0.0743、0.0725、0.0841,沿铸锭不同方向的宏观偏析均得到有效弱化。超声的空化和声流作用改变液穴中的温度场和流场,改善晶体的形成环境,促进溶质元素的均匀分布,从而细化组织、弱化宏观偏析。

Microstructure and Macrosegregation of 7050 Alloy Large Flat Billet in Ultrasonic Semi-Continuous Casting

The ultrasonic field was introduced into the casting process of the aluminum alloy 7050 flat billet with the size of 500 mm×1 320 mm.The microstructure,distribution of grain and the macrosegregation were investigated comparatively under conventional casting and ultrasonic casting.The results show that,after ultrasonic treatment(UST),the grain size is refined,and the growth of coarse-dendrites is restrained,meanwhile,the distribution of microstructure of the billet becomes more uniform.The level of macrosegregation along different direction is reduced under ultrasonic field,where the segregation index of Zn,Mg and Cu,along the symmetry axis in the direction of length and width,is decreased from 0.101 3,0.111 7,0.126 0 and 0.111 9,0.111 3,0.128 1 to 0.083 5,0.079 0,0.102 7 and 0.074 3,0.072 5,0.084 1,respectively.With the effects of ultrasonic cavitation and ultrasonic flows,the temperature field and the flow field in the liquid pool are changed,which improves the circumstance of grains formation and promotes the uniform distribution of solute elements,so refining the grain size and weakening macro-segregation behavior.