| The corrosion resistance has become the popular research because the corrosion of the AZ31 magnesium alloy restricts its widespread applications. For the moment, the studies mainly focus on adding the microelements in AZ31 magnesium alloy to improve the corrosion resistance of the microstructure. However, researches on improving its corrosion properties only by heat treatment process are hardly seen. The study can change the research thoughts of corrosion resistance in the magnesium alloy field, and it can also provide theories and test basis for the wider applications of AZ31 magnesium alloy.AZ31 magnesium alloy cast and AZ31 magnesium alloy extrusion were made by general casting and heat extrusion process. They are also under the process of annealing (T2), solid-solution (T4), aging (T5), solution-aging (T6) respectively. Their microstructures are studied by the modern test analysis methods. The corrosion-resistance rules are studied under different heat treatments by the method of weight loss and potential dynamic scanning.The study on microstructure and corrosion resistance of cast rods under kinds of heat treatments indicates that, compared with other heat treatment, solid-solution heat treatment can significantly improve efficiently the uniformity of the composition and inhibit the second phase separation of AZ31 magnesium alloy . The free corrosion potential of solution microstructure of AZ31 magnesium alloy cast is -1450mV and its free corrosion current density is 0.32mA/cm2 in the 3.5% NaCl solution saturated with Mg(OH)2. Its corrosion resistance is better than other heat-treated AZ31 magnesium alloy cast.It is also found that solution-aging heat treatment can reduce extruded base-level texture and recrystallization texture obviously. The second phase slightly and dispersedly precipitates in grains during aging, which relieves the local corrosion effect of alloy and makes the corrosion uniformly. The free corrosion potential of solution-aging microstructure is -850mV and its free corrosion current density is 0.18mA/cm2 in the 3.5% NaCl solution saturated with Mg(OH)2. Its corrosion resistance is better than other heat-treated AZ31 magnesium alloy extrusion.By the analysis of the different heat-treated microstructure and corrosion experiments of AZ31 magnesium alloy cast and AZ31 magnesium alloy extrusion, the results show that the main factors that affect the corrosion resistance of magnesium alloy cast are heterogeneous composition and the concentrated precipitation of the second phase. Owing to the effective grain refinement and composition uniform in AZ31 magnesium alloy extrusion, the main factors that affect the corrosion resistance become the base-level texture and the recrystallization texture.The comprehensive study indicates: the corrosion resistance of solution-aging microstructure of AZ31 magnesium alloy extrusion is the best in all the AZ31 magnesium alloy microstructures; the corrosion resistance of Solid-solution microstructure of cast is in the second place; the corrosion resistance of other microstructure can be arranged according to solid-solution microstructure of extrusion, annealing microstructure of extrusion , solution-aging microstructure of cast, aging microstructure of extrusion, microstructure of extrusion, microstructure of cast, annealing microstructure of cast and aging microstructure of cast in sequence. |
