Creep behavior of an AZ91 magnesium alloy reinforced with alumina fibers

Creep tests were conducted at elevated temperatures on an AZ91 alloy reinforced with 20 vol pet Al2O3 fibers. When the creep data are interpreted by incorporating a threshold stress into the analysis, it is shown that the true stress exponent, n, is similar to 3 at the lower stress levels and increases to >3 at the higher stresses. The true activation energy for creep is close to the value anticipated for interdiffusion of aluminum in magnesium. This behavior is interpreted in terms of a viscous glide process with n = 3 and a breakaway of the dislocations from their solute atom atmospheres at the higher stress levels. The threshold stresses in this composite appear to arise from an attractive interaction between mobile dislocations in the matrix alloy and Mg17Al12 precipitates. The experimental results reveal several important similarities between the creep behavior of this magnesium-based composite and the well-documented creep properties of aluminum-based composites.