Effect of cryogenic pre-treatment on aging behavior of in-situ TiB2/Al–Cu–Mg composites

• The aging behavior of the in-situ TiB2/Al–Cu–Mg composites with cryogenic pre-treatment is first studied.
• The precipitate-free zone (PFZ) induced by the TiB2 particles reduce the mechanical properties of the composites.
• A strengthening mechanism through optimizing the orientation distribution of the precipitates in the composites is proposed.

The effect of cryogenic pre-treatment aging on microstructures and mechanical properties of in-situ TiB2/Al–Cu–Mg composites has been investigated. The ultimate tensile strength and the elongation of the samples aged with a cryogenic pre-treatment are lower than the samples without cryogenic pre-treatment, while the hardness and the yield strength are higher. The decreases of the ultimate tensile strength and the elongation are attributed to the softening of precipitate-free zones (PFZs) with reduced amount of the S precipitates (Al2CuMg), which is induced by the increase of dislocation density around TiB2 particles. The increases of the hardness and the yield strength are due to the improved Orowan strengthening of the S precipitates whose orientation distribution is changed by the different stress in the matrix around the particles.