Microstructure and Mechanical Response of an Artificially Aged Al–Mg–Si Alloy: Experiments and Modeling

Abstract

An extrusion of an Al-0.65Mg-0.92Si alloy (wt%) containing 0.2 wt% Cr was selected and its isothermal aging response at 170 °C was characterized. Tensile properties were measured in the T4 (6 months at room temperature) and T6 (170 °C/10 h) conditions and differences in the yield strength and the work-hardening response are attributed to the β″ precipitates that result during artificial aging. Single crystal micropillars with [111] loading axis were milled from the alloy in the T6 condition, tested in uniaxial compression and the data were analyzed to obtain the critical resolved shear stress. Microstructure in the T4 and T6 conditions was investigated by transmission electron microscopy and dispersoids chemistry and precipitate type, morphology and size distribution were quantified; an analytical model for precipitation kinetics of β″ precipitates by assuming a cylindrical morphology and an aspect ratio that changed with aging time, has been developed and precipitates size, distribution, volume fraction and residual Mg and Si content in solid solution are determined and compared to experimental results. The intent is to eventually extend the precipitation model to understand the effect of alloy composition on precipitation kinetics and then relate microstructure evolution to flow behavior through yield strength and work hardening.