Tensile and fatigue behavior of novel dissimilar resistance spot welds of AA5754 to steels: interplay of intermetallic layer, weld nugget diameter and notch root angle

AA5754 sheet was resistance spot welded (RSW) to high-strength low-alloy (HSLA) steel sheet and low carbon steel (LCS) sheet respectively using multi-ring domed (MRD) electrodes and multiple solidification weld schedules. The confluence of the intermetallic compound layer, weld nugget diameter, and notch root angle are delineated. The results demonstrated that elevated Mn content (0.634%) in the HSLA steel promoted the formation of a thinner and more uniform IMC layer in AA5754-HSLA stack-ups when compared to the LCS, comprised of a lower Mn content (0.130%), in the AA5754-LCS stack-ups. Diluting the alloy content by changing the HSLA sheet to LCS sheet in AA5754-steel RSWs softened the aluminum weld nugget. Fatigue results demonstrated that fatigue life in Al-steel spot welds is greater when compared to the aluminum sheet joined to itself in the tensile shear configuration. Fatigue life was greater for the positive polarity AA5754-HSLA steel RSWs than for the AA5754-LCS. While weld nugget diameter dominates weld fatigue life, manipulation of the weld notch root angle enables additional fatigue life control. To enhance fatigue life, a large notch root angle is beneficial.