Effect of varying strain rates on the local mechanical properties of aluminum alloy welded joints

Synchronized stretching in conjunction with digital image correlation (DIC) was employed to obtain stress–strain curves for multiple local regions of welded joints at varying strain rates. The material intrinsic damage model for each region was then fitted using the Ramberg–Osgood equation. As such, we investigated the effects of loads with different strain rates on welded members. The microstructural distribution laws in the local regions were elucidated using scanning electron microscopy (SEM) and optical metallurgical microscopy. Moreover, residual stress concentrations were revealed by employing multi-physics field simulations during the welding process, as well as by using the DIC method for full-field strain measurements. The results demonstrated that tensile specimens with varying strain rates exhibited ductile fracturing and differed in strength and microhardness. The minimum strain-rate tensile strength recorded was 209.727 MPa, with an average microhardness of 72.66 HV0.3. Through simulations, it was further demonstrated that residual stresses and the softening zone cooperate during dynamic loading, resulting in preferential strain concentration. This study elucidates the mechanism by which the strain rate influences the mechanical properties of welded joints and the evolution of local mechanical behavior. It provides theoretical support and technical assurance for safe design and performance enhancement of aluminum alloy welded structures.