Effects of Minor Sc and Zr on the Microstructure and Mechanical Properties of Al-4.6Cu-0.3Mg-0.6Ag Alloys

Effects of minor Sc and Zr on the microstructure and mechanical properties of Al-4.6Cu-0.3Mg-0.6Ag alloys were investigated. The results indicate that Sc- and Zr-containing alloy as well as Sc-containing alloy could produce grain refinement effects. Both the alloys had lower tensile strength and hardness compared to Sc- and Zr-free alloy, mainly because solution heat treatment could not dissolve W (Al_8.5-4Cu_6.6-4Sc) phase, lowering the Cu concentration in the Al matrix. Insufficient Cu solute atoms in the Al matrix could not produce a large amount of Ω and θ′ strengthening precipitates to enhance the tensile strength and hardness following T7 heat treatment. However, the T7-treated Sc-containing alloy and the T7-treated Sc- and Zr-containing alloy have similar mechanical properties. Zirconium can partially replace expensive Sc to produce grain refinement effects on Al-Cu-Mg-Ag alloys.