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Microstructures, Surface morphology and composition of nanocrystalline Ni-Co alloy coating and Ni-Co/SiC nanocomposite coating synthesised by pulse electrodeposition have been studied by XRD, SEM and EDS. The corrosion characteristics of nanocrystalline Ni-Co alloy coating and NiCo/SiC nanocomposite coating were comparatively investigated by immersion corrosion test and electrochemical polarisation method respectively. The experimental results indicate that nanocrystalline Ni-Co alloy coatings and Ni-Co/SiC nanocomposite coatings can be synthesised by pulse electrodeposition. With introducing and increasing nano-SiC particles, the grain size of Ni-Co/SiC nanocomposite is being decreased while the microhardness is increasing. The Ni-Co/ SiC nanocomposite coating exhibited better corrosion resistance in 3?5 wt-% NaCl solution and 5 wt-% HCl solution than nanocrystalline Ni-Co alloy. The surface morphology of all samples after corrosion in 3?5 wt-% NaCl solution show evidences of little corrosion. However, samples corroded in 5 wt-% HCl solution show uniform corrosion.

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In this paper, Al2O3/7075 composites were prepared by mechanical alloying with subsequent hot-pressing sintering, and the effect of Al2O3 nanoparticle on the mechanical and tribological behavior of 7075 was studied. The mechanical property results showed that the hardness and compressive strength of Al2O3/7075 composites first increased and then decreased with Al2O3 amount increasing, and 5 wt.% Al2O3 addition made the material exhibit excellent comprehensive mechanical properties. The tribological properties also indicated that 5 wt.% Al2O3 nanoparticle significantly improved the high-temperature wear resistance of 7075 alloys. Thus, all the mechanical and tribological results confirmed that the addition of Al2O3 nanoparticle was a better strengthening way for 7075 alloys at high temperatures.

Composited ceramic coating was successfully deposited on a cast piston Al-Si system alloy ZAl12Si3Cu2NiMg using plasma electrolytic oxidation (PEO) process, and the coating mechanism that focused on the initial stages was studied systematically. The morphology, composition and microstructure of the PEO coating were analysed in detail by combination of scanning electron microscopy with energy dispersive X-ray system and X-ray diffraction. The results show that the PEO process involved three stages. The anodic oxide films were simultaneously formed on a-Al phase and eutectic Si in the initial first stage of PEO treatment, but no plasma discharge occurred on primary bulk Si phase. Both primary and eutectic Si phases prevented aluminium oxidisation and had great effects on the morphology and composition of coatings at the first stage. When voltage exceeded 300 V, plasma discharge appeared and concentrated on the localised zone of interface between a-Al and Si phase, and Al-Si-O compound formed. The silicon was oxidised into SiO 2 and mixed with Al 2 O 3 , which was formed when melted at high temperature. The roughness of coating that formed on bulk particle of silicon containing, silicon dioxide, was greater than that of other coatings that formed on other phases. When the PEO process time was long enough to get stage III, a coating with smooth surface morphology and uniform element distribution was obtained, but the microstructure of inner layer was loose due to the bulk Si existing.

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