Squeeze casting of 4032 aluminum alloy and the synergetic enhancement of strength and ductility via Al-Ti-Nb-B grain refiner

The 4032 aluminum alloy is a high-Si deformation aluminum alloy, that is commonly generated through forging due to the difficulties involved in its direct casting. In this work, the 4032 aluminum alloy is innovatively prepared via a squeeze casting process, and the Al-6Nb-1.5Ti-0.5B refining agent is incorporated to enhance its mechanical properties. A range of analytical techniques are subsequently employed to analyze the grain refinement mechanism of Al-6Nb-1.5Ti-0.5B under squeeze casting conditions. It was found that the microstructure of the aged 4032 aluminum alloy after refinement treatment was mainly composed of α-Al grains measuring <100 μm in size, in addition to a eutectic Si phase, that is accompanied by stacked dislocations and diffusely distributed Q′-Al5Cu2Mg8Si6 and θ′-Al2Cu phases. The yield strength of the alloy reached 340 MPa, its tensile strength was 400 MPa, and the elongation was 4.1 %. In the presence of the Al-6Nb-1.5Ti-0.5B refiner, the generation of nucleation cores (e.g., MAl3(M = Ti, Nb)) in the melt led to a significant reduction (∼50 %) in the α-Al grain size of the aged 4032 aluminum alloy (i.e., 95.1 ± 21.0 μm), compared with the standard alloy. After the T6 heat treatment of the refined 4032 aluminum alloy, the size of the precipitation phase was reduced by 36.8 %, and fine silicon particles with a spherical morphology and a more random distribution were observed. No obvious selective orientation was detected, and the fracture morphology improved significantly, thereby leading to a synergistic improvement in the strength and toughness of the alloy.