Process And Performance Of Electroless Plating On Magnesium Alloy

In recent years, magnesium and its alloys are widely used in various industrial fields and possess many advantageous properties that make them promising materials for a lot of applications, especially for aerospace components, automobiles, computer parts, handheld tools and so on. The excellent properties included are as follows:high strength/weight ratio, high thermal conductivity, high dimensional stability, good machinability and being easily recycled. However, corrosion is the key point that hinders its application. As an anticorrosion technology, chemical conversion coatings and electroless platings have the advantages of high efficiency, economy and adaptability. And it has an important role in corrosion protection field. This article mainly studies the behavior of Ni-P coatings of AM60B magnesium alloy after different chemical conversion.In this paper, traditional electrochemical methods and SEM, EDS, XRD are used to investigate the corrosion behaviors of AM60B magnesium alloy with different chemical conversion coatings in 3.5%NaCl solutions. The chemical conversion films combine stannate conversion film, vanadium based film and phosphate-potassium permanganate chemical conversion film. Their corrosion inhibition mechanism and effect are studied, the results showed that:all the three ways have good corrosion inhibition effect.After alkaline+acid etching, a conversion film consist of MgSnO3·3H2O is formed on the surface of magnesium alloy after stannate conversion treatment, which has the best surface morphology and corrosion characteristics. Corrosion potential of Ni-P coating after plating in bath without HF for 2h is -0.7263 V, which is greatly positive shift than that of bath with HF (-1.0179V). Corrosion resistance of coating after plating for 2h (-0.7263 V) is better than that of 1h (-1.2086V).After immersing in 30g/L Na3VO4·12H2O for 10min. the properties of the conversion film are better than other’s. Corrosion potential of Ni-P coating after plating in bath without HF for 2h is -0.5079V, which is slightly negative shift than that of bath with HF (-0.4612V). Corrosion resistance of coating after plating for 2h (-0.5079V) is better than that of lh (-1.0767V).A conversion film containing manganese which is helpful for subsequent chemical plating is formed on the surface of AM60B magnesium alloy after immersing in phosphate-potassium permanganate conversion solution. Coating from bath containing HF belongs to low phosphorus, microcrystalline range, after plating 2h its corrosion potential is positive shift 848.1mV; on the contrary coating from bath without HF but containing NH4HF2 belongs to the high phosphorus, amorphous structure, after plating 2h its corrosion potential is positive shift 328.1mV. Corrosion resistance of coating after plating for 2h (-1.1640V) is better than that of 1h (-1.2303V).After immersing in bath without HF for 2h, the corrosion potential of Ni-P coating obtained after vanadate conversion is -0.5079V, which is positive shift much more than that of stannate conversion (-0.7263 V) and phosphate-permanganate conversion (-1.1640V). The corrosion resistance is the best.