Effect of Ni on microstructure and mechanical properties of Al-Cu-Mn alloy

Abstract

The effects of Ni content on the microstructure and mechanical properties of Al-Cu-Mn alloys were systematically studied at both room temperature and high temperature. The results demonstrate that Ni effectively refines the grains. The primary Ni-containing phases in the 0.3% Ni alloy are Al3CuNi and Al7Cu4Ni phases. When the Ni content exceeds 0.3%, the dominant Ni-containing phase transforms into the Al7Cu4Ni phase. The increase in Ni content leads to the accumulation of Ni-containing intermetallic compounds at grain boundaries. Simultaneously, a significant amount of effective Cu concentration is consumed, reducing the presence of the strengthening Al2Cu phase in the alloy. Consequently, this causes a decrease in the alloy’s mechanical properties at room temperature. At a 0.3% Ni content, the alloy enriches the best high-temperature performance, revealing a tensile strength of 143 MPa at 300 °C and 94.8 MPa at 350 °C, which is 14.72% and 7 MPa higher than that of the base alloy. Due to the high thermal stability of the formed Ni-containing intermetallic compound, the grain boundary slip is effectively hindered under high-temperature conditions, thereby enhancing the high-temperature strength of the alloy. Additionally, the introduction of Ni at 300 °C effectively inhibits the growth of precipitate-free zones (PFZs). With increasing Ni content, the alloy undergoes the transition from ductile fracture to brittle fracture at room temperature. At 300 °C, the fracture evolution mode of the alloy gradually shifts from ductile fracture to ductile-transgranular mixed fracture and finally to transgranular fracture. At 350 °C, there is a gradual shift from the mixed intergranular-transgranular fracture mode to intergranular fracture.