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Influence of surfactants on the corrosion properties of chromium-free electroless nickel deposit were investigated on AZ91D magnesium alloy. The corrosion tests were carried out by immersion test (1 M HCl) and electrochemical polarization test (3.5 wt% NaCl). The surfactants in the electroless nickel bath increases the corrosion resistance properties of the deposit on the magnesium alloy. In addition, smoothness and amorphous plus nano-crystalline phase were increased and accounted for the significant corrosion resistance. As a consequence, the corrosion potential moved towards the positive direction and the corrosion current density decreased. The immersion tests also provided the same trend as that of electrochemical polarization test. On the whole, the study concluded that corrosion resistance was enhanced by including a surfactant in the electroless deposits on magnesium alloy.

High solar absorber coatings of Ni-P on aluminum substrate have been fabricated by electroless technique as an alternative to complex PVD coatings. For this purpose, the Ni-P coating was deposited on commercially pure aluminum and then blacking process was carried out. Upon heat treatment, the amorphous structure of the coatings transformed to a nanocrystalline structure which is accompanied by variation in properties. The phase structure of the coatings was studied by X-ray diffraction; the crystallite size measured by using Sherrer method indicated an average crystallite size of about 15 nm with an increase in hardness. Morphological studies of coatings were performed by scanning electron microscopy. The coatings generally had a sound, crack-free surface with a thickness value of around 10μm. The optical properties of the coatings were determined by means of spectrophotometer. The black electroless nickel possessed higher absorption in the range of visible light, with a coefficient in the order of 0.98. The results of this study indicate that the coating process described herein is suitable as solar absorber coating.