Tension-Compression Flow Asymmetry as a Function of Alloy Composition in the Al-Si System

Al-Si alloys of hypoeutectic, near-eutectic, and hypereutectic compositions, prepared from commercial pure aluminum and silicon, were investigated to study their tensile and compressive properties. The microstructures in as-cast stage were found to be refined after subsequent remelting and casting for two, five, and ten cycles. The proportion of eutectic phase and silicon particles increased with silicon content and influenced the nature of stress-strain curves. Both tensile and compressive stress-strain curves exhibited increase in flow stress with increasing strain, which could be expressed by Hollomon type relationships, but the tensile deformation occurs at lower flow stress than that in compression. While tensile specimens showed limited elongation to failure, the compression ones exhibited larger strains, up to 30% without failure. The tension-compression flow asymmetry was noted to vary as a function of the number of remelting cycles and of the silicon content in the alloy. The work hardening rate showed only stage III behavior in tension but both stage III and IV behavior in compression. The flow stress, including the yield strength, in compression was found to increase with decrease in grain size. However, in tensile deformation, instead of grain size effect, the yield strength was noted to increase with the decrease in inter-particle spacing. In both these cases, the Hall-Petch type relationships were found to be obeyed.