Creep behaviour of an oxide dispersion strengthened Al–5Mg alloy reinforced by silicon carbide particulates — an oxide dispersion strengthened Al–5Mg–30SiCp composite

The creep behaviour of oxide dispersion strengthened (ODS) Al–5%Mg alloy reinforced by 30vol.% silicon carbide particulates – an ODS Al–5Mg–30SiCp composite — is investigated at three temperatures ranging from 623 to 723 K. The creep is associated with a true threshold stress depending on temperature 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 mc reaches values as high as ∼85 and the apparent activation energy Qc values as high as ∼2000 kJ mol−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 composite matrix. The difference between the apparent and the true stress exponents as well as between the apparent and the true activation energies of creep is attributed to the strong temperature dependence of the threshold stress. The origin of the true threshold stress and its temperature dependence is discussed. Alloying the aluminium matrix with 5% Mg is shown to have only a slight effect on the creep strength of the ODS Al–30SiCp composite.