Fatigue Strength Analysis of Dissimilar Aluminum Alloy TIG Welds

Abstract

The constant amplitude loading fatigue tests were carried out on the 6061/7075 aluminum alloy TIG fillet welded lap specimens in this study, and the weld seam cross-section hardness was measured. The experimental results show that most specimens mainly failed at the 7075 side weld toes even though the base material tensile strength of 7075 is higher than that of 6061. The maximum stress-strain concentration in the two finite element models is located at the 7075 side weld toe, which is basically consistent with the actual fracture location. The weld zone on the 7075 side experiences severe material softening, with a large gradient. However, the Vickers hardness value on the 6061 side negligibly changes and fluctuates around 70 HV. No obvious defects are found on the fatigue fracture, but a large number of secondary cracks appear. Cracks germinate from the weld toe and propagate in the direction of the plate thickness. Weld reinforcement has a serious impact on fatigue life. Fatigue life will decrease exponentially as the weld reinforcement increases under low stress. It is found that the notch stress method can give a better fatigue life prediction for TIG weldments, and the errors of the predicted results are within the range of two factors, while the prediction accuracy decreases under low stress. The equivalent structural stress method can also be used for fatigue life prediction of TIG weldments, but the errors of prediction results are within the range of three factors, and the accuracy decreases under high stress.

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