In order to study the behavior of the interfaces between particles and matrix, the internal friction (IF) has been investigated in an Al-11.8Si alloy containing large silicon particles with sizes up to 10 μm. The IF spectrum exhibits a broad, poorly defined maximum situated around 240 K and a high-temperature background on which a peak centered around 485 K seems to be superposed. Moreover, the IF is increased over the whole temperature range of 100 to 550 K as the heating rate is increased or the oscillation frequency is decreased. The analysis of the experimental results is focused on the heating rate dependent contribution, δT, which is shown to be linked with the internal stresses that are induced by the difference in the thermal expansion coefficients of the silicon particle and the aluminum matrix. A model is outlined to describe δT in terms of emission or initiation of the movement of dislocation loops from the particles, which could be induced by the variation of thermal stresses during the IF spectrum measurement. A linear variation of δT versus the heating rate is derived from the model, and this law appears to be approximately followed by the experimental data. The other contributions are discussed in terms of grain boundary sliding, lattice dislocation movements, and diffusional stress relaxation around silicon particles.