Creep of AZ31 Mg alloy: A comparison of impression and tensile behavior

Creep behavior of AZ31 magnesium alloy was investigated in temperature range of 423-498 K by the localized impression creep and the conventional tensile creep testing methods, in order to evaluate the correspondence of the creep results obtained by these two testing techniques. Impression creep tests were conducted under punch stresses in the range of 125-600 MPa, while tensile creep tests were performed under tensile stresses in the range 35-140 MPa. According to the obtained results, the creep behavior could be divided into two stress regimes with different stress exponents and activation energy values. Based on the steady-state power-law creep relationship, the average stress exponents of about 3 and 6 were, respectively, obtained at the low- and high-stress regimes in both impression and tensile creep tests. The respective average impression creep activation energies of 96.9 and 139.2 kJ/mol, at the low- and high-stress regimes, were close to 93.8 and 126.6 kJ/mol determined in the tensile creep tests. Based on the obtained stress exponents and activation energies, it is suggested that the dominant creep mechanism is pipe-diffusion-controlled dislocation viscous glide in the low-stress regime, and dislocation climb in the high-stress regime. The achievement of similar creep characteristics in the employed tests implies that the localized impression creep test is capable of acquiring reliable information on the creep behavior of the present wrought Mg alloy. (c) 2012 Elsevier B.V. All rights reserved.