Characterization of magnesium spot welds under tensile and cyclic loadings

Resistance spot welds of a magnesium alloy were characterized in terms of microstructure, hardness and monotonic and cyclic properties. Microstructural features in base metal and different zones in the weld region were discussed and the mechanical behavior of spot welds in tensile–shear configuration was studied. Effects of welding parameters were investigated on the micro- and macro-scale characteristics of magnesium spot welds. To this end, five sets of spot weld specimens were prepared, utilizing different welding parameters. The effect of cyclic loading was studied on microstructure and hardness of the base metal and the weld region, and it was shown that microstructural features do not change remarkably under cyclic loading. Fatigue crack initiation and propagation behavior was discussed for different specimen sets under both low and high cyclic loads. Fatigue cracks under high cyclic loading initiated close to the nugget edge, and decreasing the cyclic load nucleated the cracks farther from the nugget.

► There is a linear trend between ultimate tensile shear load and nugget diameter for magnesium spot welds.
► Hardness of the base metal and the weld area do not change significantly after undergoing cyclic loading.
► Fatigue crack initiation location depends on the load level.
► The secondary crack length depends on both nugget size and cyclic load level.
► Primary crack propagation path is controlled by cyclic loading amplitude.