Preparation of Co-Mn Composite Conversion Coating on Aluminium Alloy by Cobalt Salt

A treating bath containing cobalt salt and potassium permanganate was used to produce an environment-friendly Co-Mn composite conversion coating on 2024 aluminium alloy surface.The fomula of the treating solution was optimized with an orthogonal experiment.The influences of solution components on the coating density were analyzed.The effects of the preparing parameters,such as solution temperature,pH value and immersion time,and the additives of wetting agent and accelerators on the surface morphology of coating were also studied.The results show that the potassium permanganate could accelerate the coating deposition on aluminium alloy.The best coating could be produced in the solution composed of 10 g·L-1Co(CH3CO2)2·4H2O,3 g·L-1 KMnO4,4 g·L-1 NaNO3,3 g·L-1 fluoride and 30 g·L-1 CH3CO2Na,and treated at 50 ℃ for 20 min with the pH value of 7.It was also found that the wetting agent and accelerator of fluoride or V salt could improve the coating effect.