Cyclic plasticity characterization of subzones in aluminum alloy joints

The heterogeneous characteristics of aluminum alloy welded joints significantly affect the overall mechanical behavior of load-carrying structures in liquefied natural gas (LNG) transport vessels. This study comprehensively analyzes the static performance, cyclic hardening behavior, and ratchetting effect of three subzones (base metal (BM), heat affected zone (HAZ), and weld metal (WM)) in 6082-T6 alloy joints, employing experiments and simulation. Cyclic plasticity constitutive models for each subzone were also developed. The results reveal that the yield strengths of the BM (320 MPa) notably exceeds that of both the WM (144 MPa) and HAZ (134 MPa). Furthermore, the hardness of the HAZ (65HV) is only 68 % of that of the WM (95HV). Under both stress- and strain-controlled low-cycle fatigue (LCF) tests, the WM exhibits the highest ratchetting strain and the most pronounced cyclic hardening, with the cyclic hardening amplitude reaching up to 152 MPa at a strain amplitude of 0.6 %. The combination of LCF testing and plastic strain amplitude simulations identifies the HAZ as the weakest region, thereby limiting the overall mechanical integrity of the 6082-T6 alloy welded joints.