Effect of Stirring Temperature on the Morphology of Primary Si Particles, Hardness and Wear Behavior of Al-20wt.%Si Alloy Prepared by Semi-Solid Stir Casting

Properties of hypereutectic Al-Si alloys depend on the size and morphology of primary Si particles. Different methods were developed to modify the morphology of primary Si particles including semi solid processes. In the present study, mechanical stirring, as a semi solid technique, was used to prepare the samples. Isothermal stirring was carried out for 10 minutes with 1600 rpm at five different temperatures. Microstructural analysis revealed that the morphology and distribution of the primary Si particles were by increasing the stirring temperature. The most prominent microstructure was achieved by stirring at 660C, the highest temperature used for stirring. With decreasing the stirring temperature, and increasing the solid fraction, the extent of agglomeration of primary Si particles increased. This in turn causes very large Si particles to form which distributed non-uniformly in the microstructure. It was also observed that the hardness of the stir cast samples depends on the stirring temperature, morphology and distribution of primary Si particles. By increasing the stirring temperature hardness increases from 54 to 76 HB and wear rate decreased from 0.0015 to 0.0008 mm3/m as a result of the refinement and uniform distribution of primary Si particles