Study On Design And Performance Of Composite Coats On Magnesium Alloy Used For Electric-control Box

As a light-weight structural metal, magnesium alloy has wide application prospect in industry, which is a competing counterpart to aluminum alloy.It is also used as artillery electric control cabinet in weapon field. However, poor corrosion resistance of magnesium alloy became a serious problem which restricted the further development application. This paper attempts to use a variety of surface treatment technology (micro-arc oxidation-organic coatings, electroless nickel plating-organic coatings and oxidation- electroless nickel plating) for coats and to study the corrosion resistance of Mg-8.5Al-1Zn alloy. The main results are as follows:The experiment of microarc oxidation-organic coatings on Mg-8.5Al-lZn alloy surface was done. SEM observation has show that the layer of micro-arc oxidation is composed dense film and loose film. The components of the film are mainly Mg, MgO and Mg2P2O7. The layer of organic silicon resin is tightly combined with the layer of micro arc oxidation. Magnesium matrix can be separated from the outside, thus its corrosion resistance is improved. The corrosion potential of composite coatings is increased by 0.072V than that of micro arc oxidation coat.The experiment of electroless nickel plating-organic coatings on Mg-8.5Al-1Zn alloy surface was done. SEM on the longitudinal section of coating showed that the surface of electroless nickel plating was dense without surface defects such as holes. Energy spectrum analysis showed that the layer of chemical nickel plating with low phosphorus (5.88%). When the plating temperature is 70℃ and the PH value is 11, the combination of the layer of electroless nickel plating and the layer of organic silicon resin are tightly; the interface between the coat and the matrix is smooth. The corrosion potential of composite coatings is increased by 0.072V than that of magnesium alloy substrate.The micro-arc oxidation and electroless nickel plating experiments on the surface of Mg-8.5Al-1Zn alloy showed that Ni particles of one layer with size in several microns are deposited firstly on the surface of porous micro arc oxidation ceramic film; the tiny particles grow up agglomerately and formed the cellular structure of ten microns in diameter gradually. Polarization curves showed that the corrosion potential of composite coatings increased 0.072V than that of micro-arc oxidation - organic silicon coating and 0.028V than that of electroless nickel plating- organic silicon coating. The test of the electromagnetic shielding effectiveness of magnesium alloy for the composite coating of micro arc oxidation (60min.) - electroless nickel plating (PH=10) was done. The results indicated that the electromagnetic shielding effectiveness of the composite coats is 70-90 db which is satisfied with the meet to electric Control box.