Creep behaviour of Ca and Bi individually added AZ91 magnesium alloy

Abstract

The combination of high specific strength and low density makes magnesium alloys a potential in engineering application. However, it suffers from poor tensile and creep properties at elevated temperatures. The present investigation studies the effect of the Ca and Bi on the creep behaviour of the AZ91 magnesium alloy. To determine the creep behaviour Impression creep testing setup was employed in which a flat ended cylindrical indenter having diameter of 1.5 mm was impressed on the specimens. All creep tests were carried out under constant punching stresses in the range of 300-480 MPa and in the temperature range of 423-523 K. The study showed that the impression creep behaviour of AZ91 alloy is significantly improved by the individual addition of Ca and Bi. It is shown that the individual Ca added alloy exhibits a superior creep resistance than the individual Bi added alloy because of the higher thermal stability of the Al2Ca phase in the former alloy compared with that of the Mg3Bi2 phase in the later one. The stress exponents values are in the range of 4.0 to 6.3 and activation energies are in the range of 105.8 ± 4.1 kJ/mol to 108.2 ± 8.3 kJ/mol, have been estimated from the alloys. Accordingly, from the stress exponent value and activation energies, dislocation climb controlled by pipe diffusion is the dominant creep mechanism for all the alloys in the temperature and stress level employed.