GROWTH OF Al_20_3/Al COMPOSITES FROM A1-Zn ALLOYS

摘要

Observations are presented here of the initiation and growth of an Al_20_3/Al composite by the directed oxidation of a molten binary A1-Zn alloy with and without preforms. The oxidation behaviour into free space begins with the formation of ZnO on the melt surface followed by a second stage of relatively high growth rate associated with the constant presence of ZnO and a final region of slow growth rate during which the surface consists of both ZnO as well as Al_2O_3. Composite formation is explained on the basis of a cyclic formation and reduction by molten aluminium of ZnO. Oxidation was carried out with ternary Mg additions into Al_20_3 preforms of different particle sizes.