Cu distribution in intermetallic phases in extruded Al-Mg-Si-Cu alloys

Primary Fe-containing intermetallic phases are formed in Al-Mg-Si-Cu alloys during industrial processes, which can change Cu distribution as well as the strength of the alloys. However, there is no literature which correlates the Cu distribution with microstructures of the intermetallic phases. In this study, we carried out microscopic analysis to characterize the Cu distributions in extruded Al-Mg-Si-Cu alloys with the focus on primary Fe-containing intermetallic phases. The primary α-phase was confirmed as the primary particle in the alloys, typically elongated along the extrusion direction. Cu was found to be enriched in α_sc-phases formed in the Si-rich Al-Mg-Si-Cu alloy, while being depleted in α_bcc-phases in the Mg-rich alloy variant. FactSage calculations suggested that α_sc-phase was more stable in Si-rich variants than in Mg-rich variants, slightly influenced by Cu content. These results suggest that it is effective to maintain more Cu atoms in solid solution by increasing Mg/Si ratio to optimize the α-phase as the α_bcc-phase.