The Pilling-Bedworth Ratio of Oxides Formed From the Precipitated Phases in Magnesium Alloys

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 Nd 2 O 3 preferentially formed from Mg 12 Nd was 1.0584, and the PBR value of Y 2 O 3 preferentially formed from Mg 24 Y 5 was 1.1923. Both the Nd 2 O 3 and Y 2 O 3 would provide a good protection to the Mg matrix. The Gd 2 O 3 preferentially formed from Mg 3 Gd, whereas the MgO preferentially formed from MgNi 2 . The PBR value of these two oxides were both larger than 2. The corresponding oxides formed from the common precipitated phases Mg 17 Al 12 , MgZn 2 , MgCu 2 , Mg 2 Ca, Mg 12 Ce, 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 Y 2 O 3 /MgO outer layer and an inner layer rich with Y 2 O 3 . The formation of Y 2 O 3 was mainly caused by the oxidation of Mg 24 Y 5 . The more Y 2 O 3 existed in the composite oxidation film, the better corrosion resistance of the Mg-Y samples.