Surface modification of Al Si Mg alloy and determination of microstructure hardness and wear rate

Abstract

An investigation was carried out to improve the hardness and the wear rate of Al Si Mg alloy using surface refining and surface alloying process. In the surface refining process the surface of the substrate is melted using the gas tungsten arc heat source and the heat source is progressively moved to form a modified layer upon solidification. The surface alloying process is similar to the surface refining process except that the substrate was pre-deposited with the alloying element which mixes with the Al-Si-Mg alloy substrate during the melting and solidification process. The alloying elements used were Ni and Ti. Ni was coated using electro-less method. Ti in the form of sheet was placed on the top of the substrate. Microstructural examination was carried out using the optical microscope. The hardness was measured using the Vickers hardness tester. The Pin-on-disc wear tester was used for wear testing. The SEM/EDAX analysis was used to determine the concentration of the alloying elements (Ni/Ti) and to identify the formation of intermetallic compound in the modified layer. The modified layer was found to have a fine grained structure due to rapid cooling occurring in this process. As a result, the hardness increased and the wear rate decreased in the modified layer when compared to the substrate. A gradient exists in the hardness profile along the depth direction of the modified layer formed in the surface refined/alloying process. It is observed that the process variables have no significant impact on the surface hardness. The hardness increases and the wear rate decreases with an increase in the Si and Ni content of the alloy. Ti also increases significantly the hardness and decreases the wear rate of the alloy. The reason for the significant increase in the hardness and the decrease in the wear rate is due to the presence of intermetallic compound in the modified layer when Ni or Ti was used as the alloying elements..