Study On The High Temperature Oxidation Behavior And Thermal Shock Resistance Of The MAO Film On The AZ91D Alloy

Magnesium alloys have excellent mechanical properties and cutting performance, but their actively chemical properties hindered the further expansion of its scope of application, surface treatment can effectively improve the corrosion resistance, abrasion resistance and heat resistance of magnesium alloys. Micro-arc oxidation technology surface treatment technology as one of the most promising technologies, has many advantages such as simple process and producding film with excellent characteristics.This article was prepared under different processing voltage to get ceramic coating on AZ91 D magnesium alloy by micro-arc oxidation technology, the film morphology and physical phase were analyzed with SEM, EDS, XRD analyzes, the thermal stability is compared with different treatments voltages by high temperature oxidation and thermal shock resistance test experiments, the impact of treatment voltage to the high temperature oxidation behavior and thermal shock resistance are discussed, the following results are obtained.The film with thickness of 37μm is obtained under 400 V voltage, the film with thickness of 17μm is obtained under 300 V voltage, the film with thickness of 10μm is obtained under 200 V voltage; the film with the treatment of heating at 400 ℃ for 128 h showed that, the film within 40μm on AZ91 D magnesium alloy by micro-arc oxidation has the higher proportion of loose layer, better blocking the action of oxygen, better reducing the weight gain, reducing the color change of the film surface, better reducing the damage to layer, longer time to maintain the integrity of the film at a high temperature with the film thickness increasing, the high temperature oxidation product consisting essentially of magnesium and oxygen; the thermal shock test at 400 ℃ was made for 50 times, Electron microscopy showed that cracks appearing sequence were samples with 200 V, 300 V and 400 V, with the increase of processing voltage, the number of cracks on the samples surface reduced, the damage to the film is reduced; the loose layer in the film increased with the voltage increasing, the overall toughness of the film reinforced to withstand thermal shock times,thermal shock resistance of the film has been improved.