Experimental Investigation of Low-Cycle Corrosion Fatigue Behavior of AA5059 Aluminum Alloy in Air and 3.5% NaCl Solution Environments

Abstract

The shipbuilding industry is increasingly adopting aluminum alloys like AA5059 over traditional steel alloys to achieve lighter structures, enhanced environmental protection, and improved energy efficiency. Ship structures are frequently subjected to fatigue loading from combined wave-induced stresses and corrosive effects. This study investigates the low-cycle fatigue (LCF) behavior of AA5059 aluminum alloy in both air and a 3.5% NaCl solution to assess the impact of corrosion on fatigue life. LCF tests were conducted at strain amplitudes of Δε_T/2 = 0.3%–0.7%. The findings indicate a marked reduction in fatigue life in the NaCl solution compared with air, regardless of strain amplitude. Back (σ_b), effective (σ_eff) stresses were assessed using Dickson's approach, showing reduced back stress and increased effective stress in 3.5% NaCl, indicating diminished hardening and enhanced plastic deformation. Corrosion was observed to enhance plastic strain energy density (PSED), with specimens exhibiting massing behavior in air and non-massing behavior in the corrosive environment. Fractographic analysis revealed corrosion pits, oxide formations, and secondary cracks in the crack initiation (CI), crack propagation (CP), and final fracture (FF) regions in NaCl. These findings on the low-cycle corrosion fatigue performance of AA5059 provide valuable guidance for its application in shipbuilding, particularly in corrosive marine environments.