Surface oxide and the role of magnesium during the sintering of aluminum

The effect of trace additions of magnesium on the sintering of aluminum and its alloys is examined. Magnesium, especially at low concentrations, has a disproportionate effect on sintering because it disrupts the passivating A l2O3 layer through the formation of a spinel phase. Magnesium penetrates th e sintering compact by solid-state diffusion, and the oxide is reduced at t he metal-oxide interface. This facilitates solid-state sintering, as well a s wetting of the underlying metal by sintering liquids, when these are pres ent. The optimum magnesium concentration is approximately 0.1 to 1.0 wt pet , but this is dependent on the volume of oxide and, hence, the particle siz e, as well as the sintering conditions. Small particle-size fractions requi re proportionally more magnesium than large-size fractions do.