DISPERSION-STRENGTHENED ALUMINIUM PRODUCTS MANUFACTURED BY POWDER BLENDING

Abstract

The microstructure of dispersion-strengthened aluminium products manufactured by powder blending has been examined by optical and transmission electron microscopy, and the mechanical properties have been determined at room temperature and at elevated temperatures by tensile- and creep-testing.

Powder variables, such as the size of the aluminium-powder particles and the size, volume concentration, and type of oxide (Al₂O₃, SiO₂, ZrO₂) used as the dispersed phase, have been investigated, together with manufacturing variables, such as temperature of the extrusion billet, reduction ratio in extrusion, and heat-treatment after extrusion. Major variables are the size of the aluminium particles and the oxide concentration, and generally it has been found that the strength increases and the elongation decreases for decreasing size of aluminium particles and increasing oxide concentration. The elongation measured after extended creep-testing is, however, practically the same for all products, of the order of 1-3%.

A subgrain structure is formed in the aluminium matrix during manufacturing. Subgrain-boundary-strengthening, which is effective at room temperature, is superimposed on oxide-strengthening; at elevated temperatures, oxide-strengthening only is of importance.

A model has been proposed that relates the flow stress (0.2% offset) to the size of aluminium particles and the oxide concentration, and good agreement with the experimental data has been found.