Formation of Al ₂ O ₃ /Metal Composites by the Directed Oxidation of Molten Aluminum‐Magnesium‐Silicon Alloys: Part II, Growth Kinetics

Abstract

The growth kinetics of an Al 2 O 3 /metal composite by the directed oxidation of an aluminum alloy (10 wt% Si, 3 wt% Mg, balance Al) have been measured as a function of temperature (1398 to 1548 K) and oxygen partial pressure in O 2 /Ar gas mixtures. The growth rate exhibited an activation energy of ∼370 kJ/mol and a dependence on oxygen partial pressure consistent with a P o 1/4 2 relationship. A dissolution‐precipitation growth mechanism is proposed in which the growth rate is controlled by the electronic conductivity of an external Al 2 O 3 ‐doped MgO surface layer in conjunction with grain boundary diffusion of magnesium.