Abstract
In order to study the influence of Mg content and holding temperature on the oxidation of molten Al-Mg (2-12%) alloys in air, oxides and their formation processes were examined by means of thermal gravimetry, X-ray diffractmetry and electron probe micro analysis. The results obtained are as follows:
The amount of oxides produced was in proportional to Mg content of the alloy, and different oxides were formed for the different holding time and temperature. On oxidation of the molten alloy, at first, Mg was selectively oxidized. And then, oxygen reacted at the interface between MgO and molten Al to produce an amorphous oxide containing Mg and Al. The amorphous oxide was crystallized to spinel type MgAl2O4 as the holding time elapsed. Owing to the difference of the reaction rate between following two reactions: Mg+1/2O2→MgO and MgO+2Al+3/2O2→MgAl2O4, at a temperature below about 775°C, the oxidation observed by the weight gain proceeded in two steps, and in one step at a higher temperature.
