EFFECT OF A SOLID-SOLUTION ON THE STEADY-STATE CREEP-BEHAVIOR OF AN ALUMINUM-MATRIX COMPOSITE

The effect of an alloying element, 4 wt pet Mg, on the steady-state cr eep behavior of an Al-10 vol pet SiCp composite has been studied. The Al-4 wt pet Mg-10 vol pct SiCp composite has been tested under compres sion creep in the temperature range 573 to 673 K. The steady-state cre ep data of the composite show a transition in the creep behavior (regi ons I and II) depending on the applied stress at 623 and 673 K. The lo w stress range data (region I) exhibit a stress exponent of about 7 an d an activation energy of 76.5 kJ mol(-1). These values conform to the dislocation-climb-controlled creep model with pipe diffusion as a rat e-controlling mechanism. The intermediate stress range data (region II ) exhibit high and variable apparent stress exponents, 18 to 48, and a ctivation energy, 266 kJ mol(-1), at a constant stress, sigma = 50 MPa , for creep of this composite. This behavior can be rationalized using a substructure-invariant model with a stress exponent of 8 and an act ivation energy close to the lattice self-diffusion of aluminum togethe r with a threshold stress. The creep data of the Al-Mg-Al2O3f composit e reported by Dragone and Nix also conform to the substructure-invaria nt model. The threshold stress and the creep strength of the Al-Mg-SiC p composite are compared with those of the Al-Mg-Al2O3f and 6061 Al-Si Cp,w composites and discussed in terms of the load-transfer mechanism. Magnesium has been found to be very effective in improving the creep resistance of the Al-SiCp composite.