Study of Strontium Effect on ADC12/Nano-Al₂O₃ Composite Characteristics with Al-Ti-B Grain Refiner Addition by Stir Casting Method

Cast iron are the common material used as brake-shoe component of the train, but this material has a high density of 7,25 g/cm³ which tends to be heavy and causes more energy consumption. Aluminum composites can be used as alternative materials with less density. For improving the mechanical characteristic of the aluminum composite, grain modification can be done using strontium (Sr) addition. This research is intended to know the effect of variation of addition of Sr as a modifier on microstructure and mechanical properties of ADC12 composite material with reinforcement of 0,03 vf% nano-Al₂O₃ particles. Composite fabrication is done by stir casting method. The addition of Mg as wetting agent was 5 wt%, Al-5Ti-B as a grain refiner was 0.04 wt%, and Sr as modified grain with varying addition as much as 0.018; 0.021; 0.026; 0.028; and 0.037 wt%. To characterize the composite product, several testing is done, which is chemical composition characterization, metallographic observation, Scanning Electron Microscopy-Energy Dispersive Spectroscopy characterization, X-Ray Diffraction characterization, hardness testing, wear testing, tensile testing, and impact testing. The results of mentioned testing generally indicate an increase in mechanical properties of the material, due to the role of Sr in the morphological modification of silicon and quasi-binary Mg₂Si, secondary dendritic arm spacing size reduction, and wetting agents in the composite system. However, excess addition of Sr will increase the %porosity of the material.