Role of grain refining in hot cracking and macrosegregation in direct chill cast AA 7075 billets

Abstract

Direct chill (DC) casting experimental results are presented for an Al–Zn–Mg–Cu alloy with and without grain refining by attempting the inoculant addition either in the furnace or in the launder at two different casting speeds. Despite considerable structural refinement macro segregation remains unchanged with grain refining at a lower casting speed. Hot cracking, on the other hand, is totally prevented at this casting speed. Depending on the grain refining practice, either hot tears do not appear at all or prior cracks existing in the non-grain refined billet are completely healed. At a higher casting speed, the severity of segregation increases. The hot cracking tendency, however, has shown a distinct difference with grain refining method, with furnace-refined alloy resulting in a crack-free billet. But the billet grain refined in the launder exhibited hot cracking. Overall, these experimental results confirm the beneficiary effect of grain refining on hot cracking.