Abstract
The true stress-true strain curves at room temperature and at 400°C were determined for various types of aluminium-aluminium-oxide products containing from 0.2 to 4.7 weight per cent of aluminium oxide and manufactured from atomized, high-temperature-oxidized and flake powder. Before testing the products were recrystallized to a grain size large compared with the interparticle spacing. The effect of particles on the initial flow stress and the flow stress for 0.2 % offset at room temperature and at 400°C is in agreement with Orowan's theory. Furthermore the effect of particles on the strainhardening rate at room temperature is great for small strains, but vanishes for large strains (>3%), at which the stress-strain curves of the dispersed products are practically parallel to the curve for aluminium of the same purity as the matrix of the dispersed product (99.5%). At 400°C practically no strain hardening is observed above a plastic strain of 0.2 per cent. The increase in flow stress at room temperature for strain values below 3 per cent was related to the plastic strain by the equation σ−gs oy = k 1ε 1 2 , where σ oy is the initial flow stress and where k 1 increases for increasing volume fraction and decreasing particle size of the dispersed particles. A general expression for k 1 was derived by means of Ashby's expression for the relationship between the dislocation density and the strain in dispersion-strengthened products.
Published Version
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