The strength of a precipitation hardened AlZnMg alloy

Abstract

An Al, 2.0 at.% Zn, 1.4 at.% Mg alloy is aged at 120°C for 3 h up to 32 days. The proof stress is determined for polycrystals. A texture analysis is preformed to obtain a reliable Taylor factor. Particle size distributions are obtained for spherical GP zones for ageing times up to 12 h and also η-particles for longer ageing times. The yield is controlled by screw dislocations in the under and overaged conditions. The experimental results are intrepreted in terms of a model for shear modulus hardening of GP zones. The incoherent η particles are overcome by the dislocations with an Orowan mechanism. A dislocation line tension model is used which depends on the dislocation configuration. The critical resolved shear stress is calculated with a statistical theory. The distribution of particle sizes and different particle positions relative to the dislocation glide plane are considered. Several properties of the dislocation at the yield stress are calculated as for example the average distance between particles. Good agreement between theory and experiment is obtained with a shear modulus of 4.3 × 10 10Pa of the GP zones.