Interplay Among Cu/Mg Ratio, Microstructure and Microhardness in As-cast and Heat-Treated Al3CuxMg Alloys

Al3Cu-(xMg) alloys are attractive materials for the aerospace and automotive industries because they are heat treatable and have excellent properties related to high specific mechanical strength. Thus, the main goal of this work is to study the influence of Mg addition in the microstructure and microhardness (HV) of Al-3Cu-xMg alloys (x = 0.3 and 1 wt%) horizontally solidified and T6-heat treated. A water-cooled horizontal solidification device was used to obtain the as-cast ingot. In turn, as-cast samples were subjected to heat treatment by T6 under the following conditions: solution at 495°C for 3 h, quenching in warm water at 70°C and artificial aging at 155°C for 15, 30, 60 and 120 min. The role of the Cu/Mg ratio was evaluated in the formation and precipitation of the θ-Al2Cu binary and S-Al2CuMg ternary intermetallic phases on the microstructure and HV in as-cast and heat-treated samples. The results showed that the typical solidification dendritic microstructure was degenerated with T6 heat treatment, but the heat treatment produced harder microstructures. A comparative analysis with the Al-3Cu-0.5 Mg alloy (wt%) from the literature was conducted. This allowed deducing that the Cu/Mg ratio = 3 promoted greater hardening after the heat treatment.