Determination of Young's modulus in aluminum alloys: Role of precipitates, dispersoids, and intermetallics

The present work was performed on Al-Si-Mg-Cu and Al-Si-Mg alloys containing measured amounts of Ni (0.4 wt.% and 4 wt.%), Bi (1.0 wt.%), Ca (0.5 wt.%), Sr (0.015 wt.%), 10 vol.%SiC(p), and 20 vol.%SiC(p). After solutionizing treatment, tensile bars (ASTM B108) were aged in the temperature range of 155 °C to 350 °C for up to 100 hours. The results of 700 tensile bars show that although the value of E is the Σ =E1+E2+ E3 +----, where E is a function of interparticle spacing and particle volume fraction of each type of precipitate, E can not be determined using a simple empirical formula due to interference of other factors such as porosity, inclusions, particle/matrix surface reaction, and precision of measuring each of the involved parameters. Considering alloying elements, the addition of a sufficient amount of Ni (Ni/Cu >1), in the T6 condition, produces the highest E value, about 92 GPa (Al 2 Cu, Al 3 Ni, Al 3 NiCu precipitates). Modification of the eutectic Si particles has a moderate improvement in E about precipitation hardening (about 12%). The highest E value was obtained using metal matrix composites (359 alloy + 20 vol.% SiC(p)) in the T6 condition, approximately 42% improvement over that achieved using the base alloy, at 110 GPa.