Artificial ageing routes in AlSi10CuX secondary cast alloys

Heat treatments and alloying are the two main approaches to control the mechanical properties of Al-Si cast alloys. Ageing treatments lead to the precipitation of metastable phases rich in copper and magnesium solutes that increase hardness. However, the recycling process increases the iron content and restricts the chemical composition to the standards of pre-sorted alloy classes, requiring optimisation of the heat treatment. Therefore, we compare the efficiency of T5 and T6 ageing routes for secondary model AlSi10Cu0.1 and AlSi10Cu2.0 alloys with increased iron content. By combining DSC and microhardness measurements with electron microscopy, we characterise the precipitates. MatCalc© simulations provide insights and predictions about precipitation kinetics and precipitate sizes. In the Cu0.1 alloy, β''-Mg5Si6, β'-Mg1.8Si, and secondary silicon precipitate in the T5 condition, while the T6 condition exclusively generates finer β''-Mg 5 Si 6 . Increasing the copper concentration to 2 wt% promotes the precipitation of Q′-AlCuMgSi laths in the T5 and smaller θ'-Al 2 Cu plates and Q′AlCuMgSi laths in the T6, respectively. Increased iron content resulted in precipitate-depleted zones around the α-AlFeMnSi phases, serving as locations for incoherent precipitates. The findings indicate that the T5 is an alternative for low-copper-containing alloys, while for higher copper contents, the T6 condition is preferable. • The T6 condition increases the peak hardness compared to the T5 by 40 % for AlSi10MgCu0.1 and 60 % for AlSi10MgCu2.0. • For AlSi10MgCu0.1-T5 secondary silicon, β’’-Mg 5 Si 6 and β'-Mg 1.8 Si are the main precipitates. The T6 condition only contains the β’’-Mg 5 Si 6 . • Q’-AlCuMgSi is the main precipitate in the Cu2.0 T5 while smaller θ’-Al 2 Cu and Q’-AlCuMgSi are present in the T6 condition. • α-AlFeMnSi intermetallics generate precipitate-depleted zones and agglomerate incoherent phases around them. • MatCalc© simulations can predict precipitate size evolution and help with DSC peak identification.