Simultaneous enhancement of strength and intergranular corrosion resistance in an Al–Cu–Mg alloy through tailored precipitation routes

In many precipitation-hardenable aluminium alloys, achieving a favourable combination of high strength and intergranular corrosion (IGC) resistance remains challenging. This is largely due to electrochemical heterogeneity arising from precipitation of second phase particles at grain boundaries (GBs) and the adjacent precipitate free zones (PFZs) developed during traditional thermal processing. Precise control of alloy microstructure achieved via controlling the distribution of solute at GBs and second phases within grains is therefore essential for enhancing IGC resistance of such alloys. The IGC kinetics is governed by GB segregation i.e., presence of grain boundary precipitates (GBPs) and PFZs. In this study, room temperature precipitation and strengthening achieved by application of cyclic loading has been explored in an Al-Cu-Mg alloy. This produces a more spatially homogeneous microstructure consisting of nanoscale solute clusters within the matrix and the absence of obvious PFZs. The propensity towards IGC was assessed in conventionally peak-aged (PA), cyclically strengthened (CS) and naturally aged (NA) AA2024 samples. PA and NA samples showed higher susceptibility to IGC due to greater solute segregation across GBs. In contrast, the CS treatment was able to achieve strengths comparable to the PA state but with a chemically more “homogeneous” microstructure which is resistant to IGC.