Creep Characterization of Aluminum-Magnesium Solid-Solution Alloy through Self-Similar MicroindentationThis Paper was Originally Published in Japanese in J. Japan Inst. Metals 69 (2005) 348--355

Indentation creep tests were performed on an Al-5.3mol% 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 in the underlying material decreases to each critical value, c and _ "c, as indentation creep proceeds, the stress exponent n for creep varies distinctively from 4.9 to 3.0. The measured c 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 1⁄4 5, m >
c or _ "in > _ "c) is approximately equivalent to that for the lattice diffusion of pure aluminum, and the Q value in range A (n 1⁄4 3, m < c or _ "in < _ "c) is close to that for the mutual diffusion of this alloy. With load-jump tests, F was abruptly increased in the indentation creep test. In range M, instantaneous plastic deformation (IPD) takes place evidently even with a slight abrupt increase in load. On the other hand, the IPD does not occur in range A when load increment is within a certain value. However, the occurrence of IPD is observed under the condition of m > c or _ "in > _ "c. The findings suggest that the creep rate-controlling process changes from the recovery control (n 1⁄4 5) to the glide control (n 1⁄4 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]