Analysis of the creep response of an Al–17Si–4Cu–0.55Mg alloy

The creep response of a hypereutectic Al–Si alloy containing 4% Cu and 0.55% Mg was investigated between 553 and 653 K. Minimum creep rate as a function of applied stress by using the power-law equation suggested the existence of two different regimes: a low-stress regime characterised by a stress exponent close to 4–5, and a high-stress regime with a higher stress exponent. Although the magnitude of the stress exponent in the low-stress regime was equivalent to that observed in pure Al, the apparent activation energy for creep was higher (Q = 210 kJ/mol) than the activation energy for self-diffusion in Al (Qd = 143 kJ/mol). The microstructural analysis suggested a similarity between this alloy and Al-matrix discontinuously reinforced composites. This approach, based on threshold-stress concept, permitted to rationalise both the magnitude of the stress exponent and the apparent activation energy for creep. In addition, the substantial similarity between hypereutectic Al–Si alloys and Al-based composites with similar composition was confirmed.