Al-Zn-Mg-Cu高强合金DC铸锭中孔洞分布的研究

Distribution of Porosity in Al-Zn-Mg-Cu High Strength Alloy DC Ingot

以DC铸造法制备的Al-Zn-Mg-Cu高强铝合金扁锭为研究对象,基于阿基米德原理测量孔洞体积分数,考察了铸锭横截面上的孔洞分布,并给出了厚度方向及宽度方向上孔洞体积分数的变化规律。结果表明,铸锭横截面上,由表层至心部孔洞体积分数呈逐渐上升的趋势;厚度方向上,由表层至心部,1/2宽度处和1/4宽度处孔洞体积分数均呈总体上升趋势;宽度方向上,1/2厚度处,由表层至心部,孔洞体积分数先迅速上升,而后在某一区间内波动;1/4厚度处,由表层至心部,孔洞体积分数先缓慢上升,而后缓慢下降。铸锭内部孔洞体积分数大小与局部冷却速率密切相关,铸锭表层附近的冷却速率快,对应孔洞体积分数较低,而靠近铸锭心部冷却速率慢,因而孔洞体积分数较高。

Al-Zn-Mg-Cu high strength alloy ingots were produced by DC（direct-chill casting）.The distribution of porosity in the cross section of the DC ingot was investigated by the precision density method（Archimeds＇ principle）.The change of porosity rate in the cross section as well as in the thickness and width direction of the alloy was presented.The results show that：at the cross section of the ingot,porosity rate is increased gradually from the surface to the center of the ingot,and at thickness direction,porosity rate in the zone of 1/2width and 1/4width exhibits an overall escalating trend from the surface to the center of the ingot.Meanwhile,at width direction,from the surface to the center of the ingot,porosity rate in the zone of 1/2thickness is firstly rapidly increased and then fluctuated in a certain range,while in the zone of 1/4thickness,porosity rate is firstly increased slightly and then decreased gradually.Porosity rate is closely related with the cooling rate in the ingot.With increasing in cooling rate,the porosity rate is decreased,while porosity rate is increased near center of the ingot as a result of low cooling rate.