Creep Parameters in a Die-Cast Mg-Al-Ca Alloy

Abstract

Tensile creep tests were conducted to determine the creep parameters for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) in a temperature range from 423 to 498 K. The stress exponent of the minimum creep rate, n, increases at the yield stress of the alloy, and it lowers at higher temperatures. The activation energy for creep, Q_c, decreases with increasing applied stress typically below the yield stress. The change in the creep parameters, n and Q_c, is associated with the decreased creep strength caused by the collapse of the eutectic intermetallic phase covering the primary α-Mg grains during creep. The thermally activated component of Q_c is evaluated to be 143 kJ/mol below the yield stress, which is very close to the activation energy for the lattice self-diffusion of magnesium. It is deduced that the creep for the alloy is controlled by the high-temperature climb of dislocations.