The effects of mould surface roughness on the hot tearing strength for an Al-4.5 percent wt Cu alloy

摘要

The effect of D.C. casting mould roughness on the microstructure and the strength to hot tearing was investigated for a Al - 4.5wt percent Cu alloy. Mould asperities are known to be preferred sites for grain nucleation and growth, due to better mould/metal contact and hence, heat transfer. Using a simple directional solidification apparatus, the binary alloy was solidified on surfaces having varied asperity densities. It was found that as surface roughness is reduced the overall grain diameter near the mould/metal interface decreases down to a minimum size. In order to reproduce the full range of grain sizes obtained in the directional solidification experiments, three surface conditions were produced at the surface of a D.C. surface simulator (DCSS) cooling plates. The hot tearing strength of the alloy was measured during solidification. Results of the tensile tests and metallographic analysis show that the samples having the thinnest liquid films in the solidified state were the strongest. This is consistent with previous studies linking hot tearing to constrained liquid films between solid grains.