An Investigation on the Effect of Chill Modification on Microstructure and ‎Quality Index of Al-15Mg2Si Composite

Cast Al-15Mg2Si composites due to appropriate specific strength and tribological properties are ‎widely used in automotive and aerospace industries. The improved properties of these composites ‎are governed by the correct controlling of morphology, size, and distribution of primary Mg2Si ‎particles. In this study the effect of solidification cooling rate (chill modification) was investigated ‎on structure and quality index of Al-15Mg2Si composite. The casting operation was performed in ‎different molds with varying cooling rates of 2.7, 5.5, 17.1, and 57.5 °C/s. According to the ‎microstructural observation and image analysis results, increasing the solidification rate resulted in ‎refinement of primary Mg2Si particles and improvement of their distribution in the matrix. The ‎increased solidification cooling rate, moreover, refined the grains so that increasing cooling rate ‎from 2.7 to 57.5 °C/s resulted in 93% reduction in grain size. These microstructural variations ‎improved the composite tensile strength, fracture strain, and quality index. The quality index of ‎composite solidified at 2.7 °C/s was found to be lower than that of composite solidified at cooling ‎rate of 57.5 °C/s by 240%.