Creep Characterization of Aluminum-Magnesium Solid-Solution Alloy through Self-Similar Microindentation

Abstract

Indentation creep tests were performed on an Al-5.3 mol% Mg solid-solution alloy to examine whether mechanical properties can be extracted accurately from a testpiece, as small as a rice grain. A conical diamond indenter was pressed into a test surface with a constant load F at temperatures ranging from 0.60 to 0.65 Tm (Tm: the absolute liquidus temperature). When the representative flow stress � � m and the indentation strain rate _ in the underlying material decreases to each critical value, � � and _ c, as indentation creep proceeds, the stress exponent n for creep varies distinctively from 4.9 to 3.0. The measured � � decreases with increasing temperature, while the corresponding indentation strain rate _ c increases under the same condition. This temperature dependence is in close agreement with the results derived from the dislocation theory. The activation energy Q for creep in range M (n ¼ 5, � � m > � � or _ > _ c) is approximately equivalent to that for the lattice diffusion of pure aluminum, and the Q value in range A (n ¼ 3, � � m � � or _ > _ The findings suggest that the creep rate-controlling process changes from the recovery control (n ¼ 5) to the glide control (n ¼ 3) below � � c. It is thus demonstrated that the indentation testing technique can be effectively used to extract material parameters equivalent to those obtained from conventional uniaxial creep tests in the dislocation creep regime. [doi:10.2320/matertrans.47.2006]