A New Precipitation-Hardening Alloy Based on the Al–Cu–Ca Eutectic System

A novel heat-treatable wrought alloy (wt. %): Al–5.6Cu–0.35Ca–0.51Mn–0.29Zr was cast as a 20 mm thick flat ingot, followed by homogenization annealing and hot rolling at 450 °C to a final thickness of 2 mm. Scanning electron microscopy (SEM) confirmed that the copper solubility in the aluminum matrix reached ~5.1 wt. %, satisfying the requirements for a pronounced precipitation hardening effect. Aging at 175 °C revealed a peak hardness of 145–150 HV achieved within ~4 h, which is comparable to the commercial 2219 alloy. Transmission electron microscopy (TEM) data suggest that the hardening is due to the formation of ultrafine coherent θʹʹ phase precipitates. Intergranular corrosion (IGC) tests showed that the new alloy performs similarly to the commercial AK4–1 alloy, with a mass loss of ~2 % after 24 h and a corrosion depth of 150–200 µm. Uniaxial tensile testing after corrosive exposure revealed a 20 % reduction in tensile strength for both alloys. Notably, the fracture mechanism in the corrosion-affected zones shifted from ductile transgranular dimpled fracture to brittle intergranular mode