Ａｌ‐４．４％Ｍｇ合金スラブ内部ポロシティの生成量の予測

Abstract

A new method for predicting porosity contents in Al–4.4%Mg DC sheet ingot (slab) was proposed. Hydrogen supersaturated mass in the interdendritic liquid and the pressure drop were taken into account for the porosity prediction. Using the method, the porosity contents were calculated and they well agreed with the experimental results. So it became possible to predict the porosity contents in the slab quantitatively. The effects of parameters such as thermal gradient, cooling rate, local equivalent pressure and initial hydrogen on the porosity contents were analytically investigated, and the distribution of porosity and porosity contents in the slab of Al–4.4%Mg alloys were determined. The following conclusions were obtained, (1) The porosity contents decrease with increasing the thermal gradient and cooling rate. But when the thermal gradient and the cooling rate are higher than 5000 K/m and 5.0 K/s, respectively, the porosity contents become almost invariable. When the thermal gradient and the cooling rate are lower than 2500 K/m and 1.0 K/s, respectively, the porosity content rapidly increase. (2) The lower the initial hydrogen contents, the lower the porosity contents become. (3) The controls of the local equivalent pressure and initial hydrogen content are necessary to reduce the porosity formation in the DC slab. (4) The distribution of porosity contents in the slab corresponds to the distribution of DAS. As the DAS becomes coarse the porosity contents become high.