Impression creep of a cast Ag-doped AZ91 magnesium alloy

Abstract

The impact of 0.5 wt% silver (Ag) addition on the creep performance of the as-cast AZ91 Mg alloy was examined through impression creep tests under stresses between 175 and 700 MPa and temperatures in the range 425–525 K. It was found that creep rates were reduced at all temperatures and stress levels following Ag addition. This improvement in creep resistance can be ascribed to a combination of microstructural modification along with reduction and a more homogenous dispersion of the β-Mg₁₇Al₁₂ intermetallic phase. The effect of Ag on solid solution strengthening, the tendency of Ag atoms to abide on the β-Mg₁₇Al₁₂ phase, and the emergence of the thermally stable Mg₄Ag particles are regarded as other influential factors. These consequences indicate that Ag is an advantageous alloying element for enhancing high-temperature creep behavior of AZ91 alloy. The creep stress exponents and activation energies acquired for the alloys under investigation were in the range 4.9–6.2 and 92–125 kJ/mol, respectively. The observed reduction in creep activation energy with rising stress levels indicates the competition between two distinct creep mechanisms, namely dislocation climb governed by pipe and lattice diffusion; the former mechanism dominates at high stress levels, while the latter is predominant at lower stress levels.