Microstructural evolution and its effect on mechanical properties in non-heat-treated AlSi9MnVZr alloy under varying process parameters

This study examines the influence of key process parameters, specifically shot speeds and intensification pressure, on the microstructure and mechanical properties of non-heat-treated high-pressure die-cast AlSi9MnVZr alloy. Using a combination of 2D microstructural analysis and 3D reconstruction techniques, it is demonstrated that the absence of fast shot speed and intensification pressure results in a coarser microstructure characterized by larger externally solidified crystals (ESCs) and increased porosity, primarily in the form of large, irregular pores. Furthermore, the absence of these process parameters also lead to insufficient localize shear stresses, which prevents the disruption of the dendritic network and inhibits the formation of eutectic bands. In contrast, the optimal set of process parameters comprising slow shot speed, fast shot speed, and intensification pressure limit ESCs growth and promote a fine microstructure by reducing melt retention time in the shot sleeve through the shot speeds, while the intensification pressure improves feeding capability and interfacial heat transfer, resulting in a more uniform microstructure with small, predominantly spherical porosity. Additionally, intensification pressure alone plays a critical role in controlling both ESCs size and porosity; a lack of intensification pressure results in the formation of larger ESCs and more widespread shrinkage pores. Mechanical testing reveals that the alloy produced under optimal process conditions, comprising appropriate shot speeds and intensification pressure, exhibits the highest strength and elongation.