Abstract
The Pilling-Bedworth ratio of oxides preferentially formed from the precipitated phases in magnesium alloys were calculated. The results showed that the PBR value of Nd2O3 preferentially formed from Mg12Nd was 1.0584, and the PBR value of Y2O3 preferentially formed from Mg24Y5 was 1.1923. Both the Nd2O3 and Y2O3 would provide a good protection to the Mg matrix. The Gd2O3 preferentially formed from Mg3Gd, whereas the MgO preferentially formed from MgNi2. The PBR value of these two oxides were both larger than 2. The corresponding oxides formed from the common precipitated phases Mg17Al12, MgZn2, MgCu2, Mg2Ca, Mg12Ce, and MgAg were all less than 1. The oxide films formed on surfaces of pure Mg and Mg-xY (x = 3, 5, 7 wt.%) alloys at high temperatures were analyzed. The results showed that the oxide films were composed of a Y2O3/MgO outer layer and an inner layer rich with Y2O3. The formation of Y2O3 was mainly caused by the oxidation of Mg24Y5. The more Y2O3 existed in the composite oxidation film, the better corrosion resistance of the Mg-Y samples.
Highlights
The PBR (Pilling-Bedworth Ratio) value of oxide film is an important parameter to evaluate the film protection performance to the base metal (Xu and Gao, 2000)
1) The PBR values of preferentially oxides formed from Mg12Nd and Mg24Y5 were 1.0584 and 1.1923, respectively, which indicated a good protection for the Mg matrix
The PBR values of preferentially oxides formed from Mg3Gd and MgNi2 were larger than 2, which existed a compressive stress
Summary
The PBR (Pilling-Bedworth Ratio) value of oxide film is an important parameter to evaluate the film protection performance to the base metal (Xu and Gao, 2000). The weight improvement ratio of pure Mg, Mg-3Y, Mg-5Y and Mg-7Y was 0.80, 0.82, 0.85 and 0.91%, respectively This phenomenon indicated that Y element had the higher activity to bind with oxygen than Mg. According to the mapping results, the difference of Y-content in Mg-xY (x 3, 5, 7 wt.%) alloys led to the different elementary composition in the oxidation products. The results depended on thickness and density of oxides films, which indicated that the oxides films formed in the surface of Mg-7Y alloy showed a best corrosion barrier effect. The PBR values of the oxide film formed from the common precipitated phases in magnesium alloys were calculated. This research is expected to provide guidance in the development of heatresistant magnesium alloys by adjusting the types of alloying elements and film formation from the precipitated phases
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