Deposition of thin tin coatings on aluminium alloys

Abstract

A systematic investigation of the immersion and electrodeposition processes of thin tin coatings used as an underlayer for the deposition of the multilayer system Cu/Ni/Cr on a typical aluminium alloy, applied in the automobile industry and other branches of mechanical engineering, was carried out. To elucidate the parameters affecting the adhesion of the tin coating and the adhesion of the protective-decorative coatings, the following characteristics were studied: the thickness of the tin coating (the current efficiency for electrodeposited tin coatings); the amount of aluminium dissolved during the deposition of the coating; the overpotential for the deposition of tin (for electrolytically deposited tin coatings) on pure aluminium, on the aluminium alloy and on pure zinc, magnesium, chromium, manganese and iron (the main alloying components of the alloy); the distribution of the alloying components and their influence on the initial stages of the tin deposition; the morphology of the alloy surface before and after the deposition of the tin coating. It is shown that iron in the aluminium alloy is distributed preferentially in the form of segregates and provides active sites for the formation of the thin tin coatings on the aluminium alloy. It is suggested that the iron segregates in the stannate treatment of iron-containing aluminium alloys determine the adhesion of the electrodeposits.