Microstructural processes in creep of an AZ 91 magnesium-based composite and its matrix alloy

Constant stress tensile creep tests were conducted on an AZ 91–20 vol.% Al2O3 short fiber composite and on an unreinforced AZ 91 matrix alloy. The creep resistance of the reinforced material is shown to be considerably improved compared with the matrix alloy. The creep strengthening arises mainly from the effective load transfer between plastic flow in the matrix and the fibers. Microstructural investigations by TEM revealed good fiber–matrix interface bonding during creep exposure. The microstructures of the AZ 91 alloy and its composite were similar with regard to two types of β-phase precipitates; the enhanced precipitation of the Mg17 (Al, Zn)12 phase on the fibers is promoted by heterogeneous nucleation due to the Al enrichment of the matrix near to the alumina fibers.