Precipitation behavior and change of yield strength during artificial aging in Al-Zn-Mg-Cu alloys

Abstract

Three 7000 type Al-Zn-Mg-Cu alloys were artificially and isothermally aged at 393 K. A small-angle Xray scattering technique was applied. Size, interparticle distance and volume fraction of precipitated metastable phase increase with prolonged aging time, but the difference of electron density inside and outside the precipitates remains constant. The precipitates has chemical composition similar to that of η’ phase. The yield strength is strongly correlated with the structure of fine metastable precipitates. If the precipitates are 2 nm or less in average radius, the cut-through mechanism dominates the interaction of dislocations with precipitates. When the precipitates grow in size, the yield stress is mainly governed by the Orowan mechanism. The observed values are quantitatively explained by the Hirsch and Humphreys’ theory. © 1984, The Japan Institute of Light Metals. All rights reserved.