Influence of natural aging on the precipitation hardening of an AlMgSi alloy

Abstract

The influence of natural aging on precipitation hardening of an Al–Mg–Si alloy was investigated by<br />mechanical testing and quantitative transmission electron microscopy. It was found that natural aging<br />increases yield stress and reduces ductility, which is attributed to the formation of Mg/Si clusters. The<br />evolution of tensile properties saturates after around 7 days natural aging. Artificial aging for 30 min at<br />180 ◦C after solution treatment resulted in an important increase in yield strength and loss of ductility,<br />due to the rapid precipitation of the intermediate phase. Previous natural aging progressively reduces<br />the strengthening effect of 30 min/180 ◦C artificial aging, completely suppressing it after 7 days pre-aging.<br />Microhardness evolution during 180 ◦C artificial aging was followed in samples that were aged immediately<br />after quenching, and with 7 days natural aging before artificial aging. In addition, microstructural<br />characterization using TEM was carried out at specific artificial aging times. Previous natural aging was<br />found to reduce the initial hardening rate, producing a delay in the formation of precipitates. The<br />peak-aging condition was reached almost at the same aging time. However, longer precipitates with<br />a lower volume fraction were observed when artificial aging was preceded by natural aging.