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摘要
Magnesium alloys are very important for lightweight applications. Industrially, these alloys cannot be used without some necessary processing to improve their corrosion properties. The most widely used methods include coating, surface treatments and cladding. In these processes, the magnesium oxide scale plays an important role in the bonding mechanism between the substrate and the coating or the cladding materials. The aim of this study is to understand the spontaneous oxide formation and the initial oxidation kinetics of the TRC AZ31 magnesium alloy. The results are important for the understanding of the subsequent surface treatment processes of that alloy. Therefore, the study comprises: first, the analysis of the native oxide which forms spontaneously after Twin Roll Casting of an AZ31 magnesium sheet, and second, the investigation of the oxidation behavior of the AZ31 magnesium alloy heated in air at 300 A degrees C with different exposure times ranging from 1 to 180 min. The results showed that the thickness of the native oxide is 5 nm and the oxide surface mainly comprises of magnesium, oxygen, and carbon compounds. The oxide film contains magnesium oxide in the form of MgO as the main oxide compound with a very thin layer of MgCO3 and Mg(OH)(2). The X-ray photoelectron spectroscopy results revealed two stages of oxidation kinetics during exposure to 300 A degrees C. Rapid growth represents the first stage, which lasts for about 30 min. After that period, the oxide growth slowed, indicating a steady state character, where the oxide film growth approaches a limit value. This slow growth is due to the lack of diffusion of oxygen into a dense oxide layer possessing a low concentration of defects. The oxidation kinetics follows an inverse logarithmic law.
- 出版日期2014-6
