Porosity in cast and directionally solidified AI and AI-Cu alloys

Abstract

Porosity in Al and AI-Cu alloys has been examined in cast and directionally solidified material for a range of hydrogen concentrations and freezing rates. The results indicate that no macrosegregation of hydrogen occurs during the freezing process. At low hydrogen concentrations and high freezing rates, pores tend to be small, spherical, and uniformly distributed interdendritically throughout the metal. At higher hydrogen concentrations and lower freezing rates the pores tend to be fewer and larger. In directionally solidified rods, elongated pores are produced at low freezing rates and higher hydrogen concentrations. The marked decrease in porosity observed in the centre of castings and in rods solidified upwards is attributed to the growth and rise of gas bubbles to the surface of the melt.