Precise Analysis of Microstructural Effects on Mechanical Properties of Cast ADC12 Aluminum Alloy

The effects of microstructural characteristics (secondary dendrite arm spacing, SDAS) and Si- and Fe-based eutectic structures on the mechanical properties and failure behavior of an Al-Si-Cu alloy are investigated. Cast Al alloy samples are produced using a special continuous-casting technique with which it is easy to control both the sizes of microstructures and the direction of crystal orientation. Dendrite cells appear to grow in the casting direction. There are linear correlations between SDAS and tensile properties (ultimate tensile strength σ_UTS, 0.2 pct proof strength σ_0.2, and fracture strain ε_f). These linear correlations, however, break down, especially for σ_UTSvs SDAS and ε_fvs SDAS, as the eutectic structures become more than 3 μm in diameter, when the strength and ductility (σ_UTS and ε_f) decrease significantly. For eutectic structures larger than 3 μm, failure is dominated by the brittle eutectic phases, for which SDAS is no longer strongly correlated with σ_UTS and ε_f. In contrast, a linear correlation is obtained between σ_0.2 and SDAS, even for eutectic structures larger than 3 μm, and the eutectic structure does not have a strong effect on yield behavior. This is because failure in the eutectic phases occurs just before final fracture. In situ failure observation during tensile testing is performed using microstructural and lattice characteristics. From the experimental results obtained, models of failure during tensile loading are proposed.