Mechanical and microstructural observations during compression creep of a short fiber reinforced AlMg metal matrix composite

The constant load compression creep behavior of a short fiber reinforced aluminium-5 wt.% magnesium alloy (AlMg5) containing 15 vol.% Al2O3 fibers (Saffil) was investigated. Creep of the matrix alloy and the metal matrix composite (MMC) was studied at 300 °C and 500 °C. Stresses ranging from 10 MPa to 120 MPa result in minimum creep rates between 10−9 s−1 and 10−3 s−1. MMC creep is characterized by an initial decrease of the creep rate before a distinct creep rate minimum is reached, while the matrix alloy shows increasing primary creep rates at 500 °C. It is difficult to rationalize the stress dependence of the minimum creep rates by a simple Norton law, because the stress exponent n is not always constant. The orientation of Al2O3 fibers with respect to the loading axis is found to affect minimum creep rates. Fiber breakage represents an important damage mechanism. Fiber agglomerates are observed in the initial microstructure which may well affect the entire process of creep.