Poisoning in Grain Refinement of A319 Aluminum Alloy and Its Effect on Hot Tearing

Aluminum alloy A319 is one of the most commonly used aluminum casting alloys. This alloy possesses good strength and excellent wear resistance. However, when A319 is processed via the permanent mold casting (PMC) process, it shows a high susceptibility to hot tearing. Grain refinement has shown promise as a means to eliminating hot tears. In this study, the effect of the grain refiner on hot tearing of A319 was investigated during PMC. Titanium was added in four levels (0.15, 0.20, 0.25 and 0.30 wt%) in Al-5Ti-1B cut rod form to A319. The results suggest that Ti additions reduced grain size in A319, but did not eliminate hot tears. Scanning electron microscopy (SEM) identified a Ti-Si compound, which likely poisoned the grain refining efficiency of the Ti-B grain refiner. As a result, the grain morphology of A319 remained dendritic, despite the addition of grain refiner, which thereby resulted in no elimination of hot tears.