Study On Composite Electroless Plating On Magnesium Alloy

In recent years，automobile pollution is more serious due to development of automobile.The fuel consumption can be reduced by decreasing weight of automobile, in which wheel isthe key parts. The use of magnesium alloy wheels, not only can reduce vehicle weight, butalso can obtain more excellent safety and damping performance. Therefore, the magnesiumand its alloy is easy to be corrosied, thus, the research on the surface protection technologyof magnesium alloy is an important direction of the development of automobile materials.The electroless plating has the advantages such as, uniform coating, good corrosionresistance, low cost, easy welding etc.Two kinds of chemical conversion coating pretreatment(A0: KMnO4pretreatmentprocess;A1: H3PO4pretreatment process) for eletroless plating were researched in this study,so as to use the new pretreatment process instead of the conventional pretreatment process. Inthis way, the coating with good performance can be obtained. The formation mechanism ofelectroless plating film was analyzed by using of EDS/XRD/SEM and the influence oftemperature on the structure and properties of plating was also studied in this paper. Theresults show that:1. Compared with A0pretreatment process, the plating of A1is denser; Paste paper testsshowed that when the matrix roughness is above Ra3.2, coating porosity reached the highest30%; XRD analysis showed that the film of A0process is mainly composed of MgMn2O4andMgAl2O4; the film of A1is mainly composed of Mg3(PO4)2and Mg3(BO3)2;2. Tensile tests showed that the pretreatment process have a definite impact on the bindingforc between matrix and plating;A0binding force was significantly lower than A1process andthe binding force of A1reached its maximum13MPa in Ra3.2;3.The different plating temperature result in the changes of cell-like’s diameter and shapefactor; Temperature also had an impact on the morphology of the plating’s cross-section;whenthe temperature is90℃, the prosity between matrix and plating is high.4.Temperature has a great effect on the plating structure and composition, the phosphoruscontent of plating reached to the peak at80℃and the plating is the most compact and smooth;The different plating structure and composition lead to the different corrosion resistance: Tafel slope analysis shows that, when the temperature is80℃, plating corrosion potential moved to-0.85V, the corrosion rate was the lowest and the corrosion resistance is highest; Thescratch test shows, the binding force of the plating drop to the lowest when the paltingtemperature is90℃.