Abstract

Metallic coatings can be used to improve the wear and corrosion resistance of aluminum alloys. A method for modifying the surface of aluminum alloys by electrochemically nickel was developed. The deposition was carried out in a stirred standard bath (Watt), the deposition was undertaken for different durations using a galvanostatic technique. The samples were subjected to mechanical polishing followed by surface pickling and activation by a zincate bath. Electroplating was carried out in a Watt bath with a current density of 2A/dm², a pH of 4.2 and a bath temperature of 45C. The time effect of the deposition on the deposit thickness and on the deposited nickel microhardness was studied.

The results show that the thickness of the layer increases rapidly during the first instants of electrodeposition and then tends towards stabilization of the thickness for the long periods. This was explained by the saturation of the surface exposed to the coating. The same pace was recorded with the microhardness. The latter increases rapidly and then stabilizes at a limiting value.

In order to reinforce the deposition layer and improve the surface properties by diffusion between the substrate and the layer, an isothermal annealing treatment was carried out at a temperature of 450 C. for different durations (30 min - 41 hours). The results show that the microhardness of the deposited layer after annealing increases gradually as the treatment time increases and approaches a limit value of around 626Hv, the measured microhardness is a microhardness of composite phase formed the surface or the surface alloy thus prepared.

Keywords"electrochemical deposition, aluminum alloy, Nickel coating, surface alloy.