Creep behaviour of an oxide dispersion strengthened Al-5Mg alloy reinforced by silicon carbide particulates - an oxide dispersion strengthened Al-5Mg-30SiC(p) composite

The creep behaviour of oxide dispersion strengthened (ODS) Al- 5%Mg alloy r einforced by 30vol.% silicon carbide particulates - an ODS Al-SMg-30SiC(p) composite - is investigated at three temperatures ranging from 623 to 723 K . The creep is associated with a true threshold stress depending on tempera ture more strongly than the shear modulus of the matrix solid solution. At applied stresses only slightly higher than the true threshold stresses, the apparent stress exponent m(c) reaches values as high as similar to 85 and the apparent activation energy Q(c) values as high as similar to 2000 kJ mo l(-1) at 673 K. However, the true stress exponent is close to five and the minimum creep strain rate is controlled by the lattice diffusion in the com posite matrix. The difference between the apparent and the true stress expo nents as well as between the apparent and the true activation energies of c reep is attributed to the strong temperature dependence of the threshold st ress. The origin of the true threshold stress and its temperature dependenc e is discussed. Alloying the aluminium matrix with 5% Mg is shown to have o nly a slight effect on the creep strength of the ODS Al-30SiC(p) composite. (C) 1999 Elsevier Science S.A. All rights reserved.