Anomalous Behaviour for Microhardness of Al-3wt.% Mg alloy

Abstract

Microhardness measurements, H, were obtained for sheets of Al-3wt.% Mg alloy in the temperature range 443-503 K, applied loads 10-300 gm and dwell times 10-40 sec. The age-hardening curves showed off leveling and pronounced oscillations indicating instability reflecting a competition between the effect of dynamic recovery or sub-structures coarsening and the effect of solute drag and precipitation hardening. The indentation size effect index (ISE), m, was calculated as 2 for the binary alloy indicating that, H, is independent on indentation size. Increasing temperature, T, load, L, and dwell time, t, caused a decrease in, H, due to the decrease of the amount of free Mg available for further precipitation hardening during the aging process. In general, increasing temperature, dwell time, applied load caused a decrease in hardness.