Experimental Observations of Dendrite Coarsening & Al-Si Eutectic Growth in Progressively Quenched Structures of Al-Si-Cu Casting Alloys

Computer controlled thermal heating and cooling curve cycles of the W319 (Al-7.5Si-3.5Cu-0.3Fe) and the WA328 (Al-9Si-lCu-0.3Fe) alloy samples were studied in this work. Both alloys contain residual levels of Sr (∼ 20 ppm max) and are processed with no grain refiner. From the cooling curve portion of the thermal cycle the characteristic temperature points that represent phase nucleation and growth are established. Once characteristic temperatures in the alloy samples are known, strategic quench points can be chosen to reveal the evolving mushy state using metallographic examination. In particular the growth kinetics of primary α-Al dendrites in quenched and unquenched alloys are studied and discussed in this work. In addition, growth modes for the Al-Si eutectic lamellae and polyhedral Si particles were also observed from quenched test samples during and post the Al-Si nucleation temperature event.