The effect of section thickness and intensification pressure on the microstructures of non-heat-treated AlSi9MnVZr Alloy

Abstract

This research systematically analyzed the effects of section thickness and intensification pressure on the microstructural features and mechanical properties of non-heat-treated AlSi9MnVZr alloy fabricated through high-pressure die casting (HPDC). By varying section thicknesses from 1 mm to 5 mm, both with and without the application of intensification pressure, the study aimed to elucidate their impact on solidification behavior, grain size distribution, porosity characteristics, eutectic band formation, and hardness profiles. Key findings demonstrated that reduced section thickness facilitated rapid cooling, resulting in a finer and more uniform grain structure. The application of intensification pressure improved the uniformity and slightly reduced the size of externally solidified crystals (ESCs), whereas the application of intensification pressure significantly decreased volumetric porosity and the number of pores across all section thicknesses due to enhanced feeding capacity and increased interfacial heat transfer coefficients of the molten metal. Eutectic bands were observed within the section thicknesses of 2 mm to 5 mm for samples subjected both with and without intensification pressure. These eutectic bands became more distinct under the application of intensification pressure. The width of the eutectic band broadened as section thickness increased due to the prolonged solidification interval and the development of dendritic ESCs. Additionally, the eutectic bands tended to shift closer to the center in thicker sections. The study also revealed that the combination of solidification rates and metal velocity under varied section thicknesses played a crucial role in the formation of eutectic bands. Furthermore, hardness testing revealed that the eutectic band region consistently exhibited higher hardness values compared to both the center and surface regions across all section thicknesses. This increased hardness is attributed to a higher fraction of eutectic, which effectively resists deformation.