Fabrication and study of electrochemical, mechanical & tribological properties of Al alloys coatings by cold spraying
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Low density, high strength and anti-corrosion materials have become very important with the advancement in the automotive and aerospace industry. Among the several lightweight materials, Magnesium (Mg) and its alloys are the most important because of their remarkable physical and mechanical properties for various aerospace applications. However, the high corrosion susceptibility and low wear resistance of Mg alloys restrict their wider use. There are various surface modification techniques that may improve the surface performance of Mg alloys but these existing techniques are limited due to their high cost and reliability. The emerging cold spray technique can be foreseen as the most suitable technique for the surface protection of low melting temperature alloys because of its low spraying temperature (200 - 900 °C) and high velocity. Even though the cold spraying process has been developed there is a critical need for an in-depth study and optimization of the process to overcome the corrosion problems for Mg alloys. In this dissertation, I have investigated in detail the electrochemical, mechanical and tribological properties of cold sprayed Al and its Alloy coatings on AZ91D Mg alloy substrate for various aerospace applications. I have studied the optimization of the process parameters of cold sprayed Al coatings and its electrochemical and tribological properties. I have performed thorough studies on the effects of 6061 Al alloy coatings on the corrosion resistance and wear properties of AZ91D Mg alloy substrate and have investigated the microstructural annealing response of cold sprayed Al and 6061 Al alloy coatings. The densification, grain size increment and increase inter-particle bonding was attributed to the heat-treatment improvement on the electrochemical and tribological properties of the coatings. The effects of heat-treatment on the residual stresses of cold sprayed Al alloy coatings were investigated by X-Ray diffraction. Our studies revealed that the electrochemical, mechanical and tribological properties of the cold sprayed coatings can be further enhanced by the heat-treatments described in this work. Our results suggest that the cold sprayed Al Alloy coatings can be effectively used in different areas of the aerospace industry.