Simultaneous strength enhancement, melt purification, and hydrogen resistance via trace Cu/Al2Cu precipitation by controlling Cu addition in Al-5Si alloys

The alloying element Cu plays an important role in the 2xxx, 6xxx, and 7xxx Al alloys due to its special alloying capability. However, the influence of alloying Cu in 4xxx series Al alloy is unknown. In this paper, the effects of the microalloying Cu on the solidification microstructure, mechanical properties, and hydrogen content were investigated, and the underlying mechanisms were determined. Over the range of 0.01–0.20 wt% of Cu addition, it demonstrates that the morphology of eutectic Si and Fe-rich phase is modified. The ultra-tensile strength (UTS) of the casting state alloy, extrusion rod, drawing rod, and annealing rod all increases whereas the elongation (EL) of them decreased slightly with Cu content. Specifically, when Cu addition is 0.03 wt%, the hydrogen content decreases to the lowest value, 63 % of that of the alloy without Cu, and the quality factor (Qi) reaches the highest value. It shows that it is Al 2 Cu phase precipitated in α-(Al) matrix and segregation of Cu atoms at the grain boundaries that are responsible for the increasing strength while slightly reducing plasticity. Our findings offer a novel approach to optimizing performance via microalloying with Cu and pave the way for enhancing the properties of Al-Si alloys.