| Magnesium alloy is the lightest metal material in actual productive application. It has many excellent performances, such as high strength-weight ratio, excellent castability and cutting properties, easy recovery and so on. Nowadays magnesium are used widely in automotive, electronic and aeronautical industries. However,magnesium alloy`s applications are restricted by its poor corrosion for the active chemical properties of magnesium. Therefore the research and the improvement of the corrosion resistance of magnesium alloys have become a heat-point.For the moment, the researches of improving the corrosion resistance of magnesium alloy focus mainly on two aspects: 1) Changing the microstructure of the magnesium alloy by adding trace elements or changing the solidification process of magnesium alloy casting process. 2) Isolating magnesium alloy substrate from corrosion environment by surface modification and surface coating technology to improve the corrosion resistance of magnesium alloy. But the research of improving the corrosion resistance of magnesium alloy by changing the microstructure of magnesium alloy using heat treatment is still less. The affects of heat treatment of AZ31(AZ63) for the microstructure and corrosion resistance of magnesium alloy were mainly studied in the paper.AZ31 magnesium alloy cast were made by general casting and heat extrusion process and then it was treated with different process, including annealing,solid-solution, aging and solution-aging respectively. Their microstructures and corrosion resistance are studied by methods of XRD, SEM, weight loss and potential dynamic scanning.The study on microstructure and corrosion resistance of the microstructure of AZ31(AZ63) magnesium alloy using heat treatment showed : Solid solution and aging treatment can increase the uniformity of the microstructure of magnesium alloy.According to data of weight loss, corrosion resistance of two kinds of heat treatment are similar and are better than cast. Potentiodynamic scanning results shows that the corrosion current in 3. 5wt. %Na Cl solution of magnesium alloy decreases after solution and aging treatment.The microstructure and weight loss of AZ31 and AZ63 shows: Annealing and aging treatment of magnesium alloy will both reduce its corrosion resistance.Compared with the data of weight loss, the average corrosion rate of AZ31 is 5%higher than that of AZ63. The data can be obtained by potentiodynamic scanning,the free corrosion potential of solution microstructure was-1260 m V(AZ31) and-1210 m V(AZ63), the free corrosion current density was 0. 32 m A/cm2(AZ31) and 0.29 m A/cm2(AZ63); the free corrosion potential of solution-aging microstructure was-1230 m V(AZ31) and-1260 m V(AZ63), the free corrosion current density was 0.42 m A/cm2(AZ31) and 0. 47 m A/cm2(AZ63).The comprehensive study indicated: the corrosion resistance of solution-aging microstructure of AZ63 magnesium alloy is the best, the corrosion resistance of other microstructure can be arranged according to solid solution of AZ31, solution-aging of AZ31, solution-aging of AZ63. For annealing and aging treatment, both of which will reduce the corrosion resistance of magnesium alloy. |
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