Influence of Si and cooling rate on microstructure and mechanical properties of Al-Si-Mg cast alloys

This paper aims to investigate the effect of Si-content and microstructure on mechanical properties of Al-Si-Mg alloys with the purpose of to develop high-strength cast aluminum alloys that are anodizable. The Si-content was 2.5, 3.5 and 5.5 wt% Si, and both Sr-modified and unmodified conditions were used. The samples were produced using the gradient solidification furnace to generate a well-controlled microstructure. The resulting secondary dendrite arm spacing was 10 and 20 mu m. The microstructural features were evaluated by employing SEM/EDS and optical microscopy. Furthermore, computed tomography (CT) scan technology was used to provide a 3D view of high-density phases in the microstructure. The mechanical properties of these alloys were studied by means of tensile and hardness testing where the latter was performed on the macrolevel and microlevel. The results demonstrate clearly how the Si growth in the microstructure is restricted by increased cooling rate and modification and its role in strength development in Al-Si alloys. Additionally, the CT scan visualized the morphology of intermetallics and supported in identifying the oxide layer growth as a result of the anodizing process. Copyright (C) 2015 John Wiley & Sons, Ltd.