Comparison of the semi-solid constitutive behaviour of A356 and B206 aluminum foundry alloys

Abstract

The semi-solid constitutive behaviour of two commercially important aluminum foundry alloys, AA B206 and AA A356, has been quantified using a Gleeble thermo-mechanical physical simulation system. For these tests, a series of samples were extracted from a directionally-solidified wedge casting. The samples were further classified by their microstructure, average grain size of 128, 220, or 325 μm for B206, and average secondary dendrite arm spacing (SDAS) of 43, 90, or 124 μm for A356. The results indicate that at high solid fraction, 0.95<fs<1, B206 had a higher yield stress than A356. However, at lower solid fraction, fs<0.95, A356 had the higher yield stress. In both alloys, an increase in the microstructure (grain size or SDAS), resulted in a decrease in the semi-solid ductility. The effect of microstructure on yield stress was minimal. The minimum solid fraction when the yield stress reached a very low value, known as the rigidity point, was shown to be 0.93 and 0.80 for B206 and A356, respectively. This significant difference in rigidity demonstrates the importance of the eutectic on reducing hot tearing susceptibility.