Development of Al356-Al2O3 Nanocomposite Coatings by High Velocity Oxy-fuel Technique

In this research, development of Al356-Al2O3 nanocomposite coatings has been investigated. Al356-Al2O3 composite powders were prepared by mechanical milling of Al356 powder and 5 vol.% micro and nanoscaled alumina particles. The milled powders were used as feedstock to deposit composite coatings on A356-T6 aluminum alloy substrate using high velocity oxy-fuel (HVOF) process. X-ray diffractometry, optical and scanning electron microscopy, microhardness and wear tests were used to characterize the composite powders and coatings. The hardness of composite coatings containing micro and nanosized Al2O3 were 114.1 ± 5.9 HV and 138.4 ± 6.9 HV, respectively which were higher than those for substrate (79.2 ± 1.1 HV). Nano and microcomposite coatings revealed low friction coefficients and wear rates, which were significantly lower than those obtained for Al356-T6 substrate. Addition of 5 vol.% micro and nanoscaled alumina particles improved the wear resistance by an average of 85% and 91%, respectively. This is mainly caused by the presence of Al2O3 in matrix and nanocrystalline structure of matrix. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.