Simultaneously enhanced mechanical strength and inter-granular corrosion resistance in high strength 7075 Al alloy

Abstract The strength and corrosion resistance of 7000 series (Al-Zn-Mg-Cu) alloys seldom co-exist and are often trade-off with each other. In present study, an alternative surface nanocrystallization technique called sliding friction treatment (SFT) was adopted to successfully generate a gradient nanostructured layer on coarse-grained (CG) peak-aged AA 7075-T6 alloy sheet. The grain size on the topmost surface of SFTed sample was extremely reduced to nano-scale (average grain size: ∼56.2 nm). Excitingly, the SFTed 7075 possessed simultaneously improved mechanical strength and inter-granular corrosion (IGC) resistance relative to the CG counterpart. Specifically, both ultimate tensile strength (UTS) and yield strength (YS) of SFTed sample are even ∼ 40 MPa higher than those of untreated peak-aged CG sample. Meanwhile, the IGC test results demonstrate that the average maximum corrosion depth is considerably reduced from ∼179 μm to ∼40 μm after SFT treatment. The obviously refined grains account for the enhanced strength, while the improved IGC resistance should benefit from SFT-induced grain refinement, elimination of both grain boundary precipitates (GBPs) and precipitates free zones (PFZs) along the grain boundaries of SFT-induced nanocrystalline. Our results demonstrate that SFT processing offers a design pathway to fabricating 7000 alloys with modified strength-IGC resistance synergy.