Prediction of porosity contents and examination of porosity formation in Al–4.4%Mg DC slab

Abstract

A new method for predicting porosity contents in Al–4.4% Mg DC sheet ingot (slab) isproposed. Hydrogen supersaturated mass in the inter–dendritic liquid and the pressure drop were taken into account for the porosity prediction. Using the method, the porosity contents were calculated and theywell agreed with the experimental results. Thus it becomes possible to predict the porosity contents in the slab quantitatively. Furthermore, the porosity generation mechanism was observed from the surface to the center in the slab. The quantities and area fractions of the porosity were measured quantitatively by using an image analysis apparatus (Luzex). An explanation of this kind of porosity generation mechanism and the distribution of the porosity was attempted by using a local equivalent pressure and hydrogen supersaturation in dendritic solidification. The effects of parameters such as therma gradient and cooling rate on the porosity contents were investigated analytically and the distribution of porosity and porosity contents in the slab of Al–4.4% Mg alloys were determined.