熔体超声处理对7050铝合金铸锭微观偏析的影响

Effect of Ultrasonic Treatment on Ingot Microsegregation of 7050 Aluminum Alloy

采用不施加超声、施加300、1 000W功率超声三种工艺处理半连铸成形7050铝合金大扁锭,并对不同铸锭的第二相形貌、溶质元素含量变化进行了分析.结果表明：经超声处理的铸锭,非平衡共晶组织变得细小而分散;超声作用下Zn、Mg和Cu元素的成分曲线较常规铸锭平缓,1 000W超声作用效果更加明显,其Zn、Mg和Cu的晶内相对溶质固溶度分别提高6.36%,19.44%和10.14%;超声处理增大了各溶质元素的有效分配系数ke值,凝固初期的增幅为0.04～0.24;1 000W超声作用使铸锭芯部及边部区域的微观偏析得到有效弱化,而芯部距离边部1/2处作用效果相对较差;由于超声加速了凝固前沿的冷却速度,使更多的溶质原子固溶到α-Al中,Zn、Mg和Cu元素在铸锭中的微观偏析得到了改善.

Aluminum alloy 7050 large scale billets were prepared with 300、1 000 W ultrasonic field and without ultrasonic field in semi-continuous casting respectively.The second phase morphology of different ingot was observed,and the content of solute elements was analyzed.The results indicate that the non-equilibrium eutectic organization becomes small and scattered in the ingot with ultrasonic.The composition curves of Zn,Mg and Cu with ultrasonic field become gentle compared with conventional ingot and the effect is more obvious with 1 000 W ultrasonic.The relative intracrystalline solubility of Zn,Mg and Cu increases respectively by 6.36%,19.44% and 10.14%,and the parameter kebecomes larger with ultrasonic field and increases significantly between 0.04～0.24 in the early solidification.The microsegregation in the edge and central portion of the ingot cross-section are effectively weakened with 1 000 W ultrasonic field,and the effect is relatively poor in 1/2part from the center to the edge.Because the cooling rate at the solidification front is promoted by 1 000 W ultrasonic field,and there are more solute elements inα-Al,the microsegregation of each element in the ingot is alleviated.