Effect of grain refiner amount on the hot tearing of 6xxx alloys during Dc casting

Abstract

In this work full scale DC casting trials of 6xxx alloy were performed. The purpose of the trials was to study the effect of the grain refiner amount on the critical casting speed at which hot tearing occurs during DC casting of extrusion ingots. Four addition rates of grain refiner were used. For each amount of grain refiner the speed of casting was increased step by step after each half meter of casting until hot tears formed in the centre of the ingots. Two alloys, AA6060 and AA6082, and one diameter, π203mm (8") were investigated. The effect of water amount on centre cracking was also investigated. The results have shown that the critical casting speed for centre cracking is highly dependent on the grain refiner addition level. Even though no further grain refiner effect could be observed in the trials high addition rates did still influence the critical casting speed. The effect of water amount on centre cracking was not significant.