Effects On Power Waveform On The Oxidation Process Of Magnesium Alloy

Magnesium is an important light metal. Magnesium alloy has a high ratio of stiffness, good thermal conductivity and electromagnetic shielding. As a kind of structural materials, it has great potential applications in aviation and automotive industry currently. However, because the standard equilibrium electrode potential of magnesium is too negative, magnesium alloy's low corrosion resistance in neutral, acid and marine environments, so improving the corrosion resistance of magnesium alloys has become an important matter. Effects on different power waveform on the oxidation process of magnesium alloy and some new oxidation processes of AZ91D magnesium alloy were studied in this paper. The results show that the corrosion resistance of magnesium alloys is greatly increased. The main works obtained are presented as follows:1. AZ91D magnesium alloy was oxidized in an alkali electrolyte solution containing borate, silicate and organic amic by alternating current(AC). The effects of electrolyte composition, oxidation voltage and time on the AC oxidation of magnesium alloy were studied. The optimal process conditions are as follows:electrolyte is 30g/L NaOH,25g/L Na2B4O7,90-120g/L Na2Si03 and 20mL/L triethanolamine, oxidation voltage is 150-190V, time is 10 minites. A smooth and compact gray-white ceramic film with good corrosion resistance is obtained under the optimal conditions. The process not only reduces the cost of oxidation treatment, but also improves the production efficiency.2. In the two components electrolyte composed of silicate and molybdate, a brown ceramic film on AZ91D magnesium alloy were obtained by using of triangular-wave voltage oxidation. when silicate is 90-150g/L, molybdate is 5-25g/L, oxidation voltage is set as 110-190V, a good film can be obtained. The film which is provided with the best quality in all processes has a significantly higher micro-hardness and excellent corrosion resistance.3. In the two components electrolyte composed of silicate and molybdate, the effects of three kinds of power supply waveforms, namely DC, AC and triangle wave on the oxidation process of AZ91D magnesium alloy and film's performance were investigated. The results show that a series smooth and dense brown ceramic films layer can be obtained by using these waveforms. At the same oxidation voltage, the film's corrosion resistance prepaved by triangle wave oxidation is the best, followed by AC oxidation, DC oxidation is the worst.