The precipitation behavior and mechanical properties of cast Al-4.5Cu-3.5Zn-0.5Mg alloy

The precipitation behavior of a cast Al-4.5Cu-3.5Zn-0.5Mg alloy was comprehensively analyzed using differential scanning calorimetry (DSC), Vickers hardness measurement, electrical conductivity measurement, and transmission electron microscopy (TEM). The results revealed that three exothermic reactions occur during the heating process of DSC, giving rise to exothermic peaks at around 130, 250, and 280 °C due to the formation of Guinier-Preston (GP) zones and the precipitation of Ω phase and θ′ phase, respectively. TEM observations indicated that the predominant phase was the Ω phase, with only small amounts of the θ′ phase precipitating at 280 °C. STEM analysis showed that elements Zn and Mg segregate at the Ω-α interface. The precipitation of the Ω phase was remarkably promoted by the addition of Zn. The tensile strength and elongation heated up to 280 °C with the heating rate of 5 °C/min were 403 MPa and 9.2%, respectively. It was thus concluded that the precipitation sequence of the cast alloy was supersaturated solid solution (SSS)→GP zone→Ω phase→θ′ phase. The cast alloy possesses high strength and high toughness due to the predominance of the Ω phase and the lack of substantial θ′ phase.