Microstructural and Morphological Evolution of Novel In Situ Al-15%Mg₂Si-4.5%Si Composite with Strontium Addition

This study investigates the effect of Sr (0.1, 0.15, and 0.2 wt.%) modification on the microstructure and morphological evolution of the in-situ Al-15%Mg 2 Si-4.5%Si composite. The composites are developed via Low superheat casting (LSC) technique, at the onset of gravity, and subsequently characterized through optical microscope, X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electron Probe Microprobe Analysis (EPMA), and XRD texture analysis. It is found that, with the increase of Sr content in the Al-15%Mg₂Si-4.5%Si composite, the morphology of primary Mg₂Si particles changes from irregular dendritic and hopper structure to nearly perfect cubic morphology. The addition of 0.2 wt.% Sr reduces the average primary magnesium silicide (Mg 2 Si) particle size from ~56 µm to 36 µm and the Al grain size from ~63 µm to ~44 µm, indicating significant refinement. The XRD texture analysis through Orientation Distribution Function (ODF) reveals that the cubic texture and rotated cubic texture are the predominant orientations for Al and Mg 2 Si phases, respectively. However, the composite modified with 0.2 wt.% Sr exhibits a weak texture and more random grain distribution, highlighting the role of Sr in reducing grain size and promoting uniformity. These findings underscore the potential of Sr addition to enhance the microstructural and mechanical properties of Al-15Mg₂Si-4.5Si composites for advanced applications.