Compressive creep behavior of a cast Al-15Mg2Si in situ composite

The microstructural evolution and creep behavior of a cast Al−15 wt% Mg2Si in situ composite was investigated by compression testing. The tests were carried out under applied stresses in the range 50-250 MPa, corresponding to 0.002≤σ/G≤0.011, at temperatures in the range 473-563 K. The microstructural studies showed that the morphology of the large primary Mg2Si particles did not change during creep deformation. On the other hand, the morphology of pseudo-eutectic Mg2Si intermetallics changes from plate-like to a finer dot-like one, where pseudo-eutectic structure is partially broken after being tested under creep stress at high temperatures. Assuming a power-law relationship between the strain rate and stress, depending on the testing temperature, stress exponents of 4.6-5.3 were obtained. Based on these stress exponents and the average activation energy of 131 kJ mol−1, it is proposed that dislocation climb controlled by lattice self-diffusion is the rate-controlling mechanism. No threshold stress was observed in the creep behavior, mainly due to the large size of the primary Mg2Si particles and the coherency of these particles with the aluminum matrix.