Creep characteristics of a diecast AM50 magnesium alloy

Tensile creep tests were conducted to examine the creep behavior of a diecast AM50 magnesium alloy in the temperature range from 423 to 498 K. A normal transient creep stage is followed by a minimum creep rate stage and finally by an accelerating stage at each creep condition. The stress exponent of the minimum creep rate, n, increases from similar to 5 at lower stresses to similar to 10 at higher stresses at each temperature, and the value of n changes at the yield stress of the alloy. The activation energies for the creep, Q(c), are determined to be 121 +/- 10 and 162 kJ/mol, at lower and higher stresses, respectively. It is concluded that the creep of the diecast AM50 alloy is controlled by the high-temperature climb of dislocations, whereas the instantaneous plastic strain introduced by the higher stress of the creep test is assumed to cause the increased values of n and Q(c).