Microstructural Modification of AlSi5Cu2Mg Alloy by Tungsten Addition and Heat Treatment

Al-Si-Cu-Mg-based alloys are key materials for applications in the automotive and aerospace industries, mainly due to their low density, excellent castability, and high specific strength. However, their mechanical properties are often negatively affected by the presence of brittle, acicular eutectic silicon particles and long intermetallic phases with a high iron content, which have a negative impact on the overall toughness and strength of the material. This study systematically focuses on evaluating the individual and combined effects of microalloying with varying amounts of tungsten and T7 heat treatment on the microstructure of the hypoeutectic AlSi5Cu2Mg alloy. The results obtained showed that the addition of tungsten significantly refines the microstructure of the alloy already in the cast state. There is a reduction in the coarse-grained morphology of the primary α-Al phase and a significant refinement of the eutectic silicon, which changes its original shape to a finer and more compact one. At higher tungsten concentrations, extensive clusters of fine grains were observed, indicating its effective role in the heterogeneous nucleation of the eutectic phase. Another key finding is its ability to suppress undesirable iron-rich intermetallic phases, particularly β−Al5FeSi acicular structures, which are transformed into shorter and more compact shapes. The combination of tungsten and T7 heat treatment further enhanced the synergistic effect and accelerated the spheroidization of eutectic silicon, promoting the formation of an almost perfect spheroidal morphology. At the same time, a significant modification of the Fe-phase shape to a less critical morphology was achieved.