Effect of multipass submerged friction stir processing on the microstructure, mechanical properties and corrosion resistance of 5383Al alloy

The 5383Al alloy is commonly used as a hull material because of its excellent mechanical properties, corrosion resistance and weldability. Nevertheless, the presence of coarse Al6(Fe, Mn) particles and the aggregation of the β phase at the grain boundaries noticeably diminish the corrosion resistance of 5383Al, even though they improve its mechanical properties somewhat. In the present study, multipass submerged friction stir processing (M-SFSP) was conducted on 5383Al alloy to precisely control the microstructure while maintaining a balance between mechanical performance and corrosion resistance. The effects of M-SFSP on the microstructure, mechanical properties and corrosion resistance of the 5383Al were investigated. The results show that homogenous ultrafine equiaxed grains of around 0.65 μm in size was acquired in the M-SFSPed zone through dynamic recrystallization. In the M-SFSPed zone, the dislocation density decreased and the proportion of high-angle grain boundaries increased. As a result, the M-SFSPed 5383Al alloy exhibited excellent and homogeneous mechanical properties, including an ultimate tensile strength of up to 400 MPa, comparable to that of the base material (BM). In addition, many fine Al6(Fe, Mn) particles were uniformly distributed in the M-SFSPed zone, and no β-Al3Mg2 phase was detected at the grain boundaries in the M-SFSPed zone. The M-SFSPed samples showed considerably lower mass loss to corrosion than the BM (1.8 mg/cm2 vs. 42.8 mg/cm2), indicating that M-SFSP increased the corrosion resistance of the 5383Al alloy through microstructure control. This improvement was attributed to the refinement of the Al6(Fe, Mn) phase and the redissolution of the β-Al3Mg2 phase, which effectively inhibited the spread of corrosion. Thus, M-SFSP is considered as a promising method for the manufacturing of 5383Al with high strength and outstanding corrosion resistance.