| Magnesium alloy has been widely used in many fields?e.g.aerospace and automotive industries?owing to its outstanding properties such as light weight,low modulus of elasticity and good electromagnetic shielding characteristics.However,the poor corrosion resistance of magnesium alloy has prohibited any further applications.In this study,physical vapor deposition?vacuum evaporating deposition?coupled with the pretreatment of the samples were employed to successfully prepare an aluminum coating on AZ91D magnesium alloy in an attempt to enhance its corrosion resistance with lower energy consumption,pollution and cost.The morphology,corrosion resistance and adhesive strength of the samples prepared from different pretreatments?mechanical polishing and different acid etching?were systemically investigated.The effect of deposition time and annealing treatment on the morphology,corrosion resistance and adhesive strength was also examined.The results show that the best corrosion resistance after deposition of aluminum comes from the sample pretreated by H3PO4 etching.The corrosion resistance is increased by about30 times after deposition and the corresponding aluminum coating shows the highest adhesive strength.As the deposition time increases,a continuous and dense aluminum coating gradually forms on the surface of magnesium alloy following the typical island growth?Volmer-Weber?mode.The increase of deposition time enhances the corrosion resistance of magnesium alloy but has no effect on the adhesive strength between the coating and the substrate.With the increase of the annealing temperature,the coating of the sample becomes more uniform with better crystallinity of aluminum compared with non-annealed sample.The adhesive strength increases,whereas the corrosion resistance declines. |
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