Characteristics of microstructure and fatigue resistance of hybrid fiber laser-MIG welded Al–Mg alloy joints

Effect of microstructural features on the failure behavior of hybrid laser welded AA7020

“…S‐N curves of both the base metal and welded joint indicate a reasonable fitting to a linear regression line, and the standard error of the linear regression is determined to be 0.07 and 0.13, respectively. The slopes of 2 S‐N curves are different mainly due to different fatigue performance . The fatigue strength of hybrid joints is 96 MPa at 50% survival probability under N f = 2 × 10 6 cycles, which corresponds to 37% of the ultimate tensile strength of welded joints.…”

“…According to the Hall‐Petch equation, the contribution of grain to the strength is inversely proportional to the square root of grain diameter . As discussed in Section , the grain size of FZ is slightly larger compared with the base metal, giving a lower yield strength and hardness.…”

“…The striation spacing is usually equal to the crack increment in 1 cycle when the FCG is at stage II, determined by the applied loading, microstructure, and environment. The normal direction of the striation can be changed by the grain orientation, intermetallic particle, and gas porosity …”

“…5,[8][9][10][11] It is shown that the HLW can improve the mechanical and fatigue property of Al-alloy joints over those from individual arc welding or laser welding. 5,7,[12][13][14] Although these findings clearly indicate a great potential for the application of HLW to Al alloys, huge challenges still exist, such as considerable porosity, softening behavior, and degraded fatigue performance under reversed cyclic loading. 13 Note that primary metallurgical defects such as gas porosity are well known not to be completely eliminated despite of the advanced welding method subjected to optimum processing parameters and proper filler materials.…”

“…It is shown that the HLW can improve the mechanical and fatigue property of Al‐alloy joints over those from individual arc welding or laser welding . Although these findings clearly indicate a great potential for the application of HLW to Al alloys, huge challenges still exist, such as considerable porosity, softening behavior, and degraded fatigue performance under reversed cyclic loading …”