Impression Creep of Lightweight Alloys 2010-01-0226

Conventional creep testing requires many samples and therefore is time consuming and inconvenient. The impression creep technique is a new creep test wherein a cylindrical, flat-tipped punch is pressed into the material and the displacement recorded as a function of time. Due to the constant contact area between the punch and specimen, a steady-state deformation can be reached underneath the punch, from which the creep parameters can be obtained. In the present study, the creep behaviors of two lightweight magnesium alloys were studied by using impression creep tests in the temperature range of 408-443K and under the punching stress range of 1.68-60.4 MPa. Using a power law between the steady-state impression velocity and the punching stress, it was found that the stress exponent changes with both stress and temperature. In the high temperature range, the stress exponent n for MRI 230 is ~ 6.7 while for AZ91D is ~ 5.5. The activation energy for MRI 230 is 78.9 kJ/mol and for AZ91D is 59.5 kJ/mol.