Improving the stress corrosion resistance of 7075 matrix composites through combination of nanoparticle incorporation and retrogression re-aging treatment

7xxx aluminum matrix composites reinforced with ceramic nanoparticles are expected to possess advantageous comprehensive performance. However, further applications of these composites remain in doubt because it is likely that introducing these extrinsic phases could impair the resistance to stress corrosion crack (SCC). In this work, we used 7075 as the matrix, and TiB2 nanoparticles as the reinforcement, to study the influences of the retrogression and re-aging (RRA) treatment and nanoparticle incorporation on the SCC behavior of 7075 aluminum alloy. The intergranular corrosion test (IGCT) and slow strain rate test (SSRT) results show that both TiB2 and RRA are conducive to the improvements in the SCC resistance. The positive effects of RRA can be two-fold: (i) the lattice distortion is alleviated during the RRA temper; (ii) the coarse and discrete grain boundary precipitates (GBPs). The accumulation of active solute elements, however, also occurs at the grain boundaries, leading to severe intergranular corrosion. Surprisingly, some coarse TiB2 particles larger than the thickness of particle-free zones (PFZs) could obstruct the mass transportation, reducing the susceptibility to intergranular corrosion. In conclusion, the strength and SCC resistance of 7075 alloy can be concurrently improved by the combination of particle incorporation and RAA treatment.