Resistance spot weldability of TBF steel sheets with dissimilar thickness

This paper presents an experimental study on weldability of TBF steel sheets with dissimilar thickness. Nominal thickness of TBF sheets were 0.95 and 1.55 mm. Optical microscope was used to observe the cracks formed in the weld zone. The indentation depths were determined by ultrasonic technique. Tensile shear tests were applied to the welded specimens in order to determine the mechanical properties. Higher weld current and time resulted in higher nugget size and indentation depth. This increase in nugget size and indentation depth with increasing of weld current and weld time was almost linearly. The liquid metal embrittlement crack sensitivity in the HAZ was very high on TBF spot welds. The liquid metal embrittlement cracks were much deeper and wider along the weld periphery regions compared to the nugget regions. These cracks were occurred easily with a higher heat input and the crack depth increased almost linearly with increasing of heat input. Weld strength of the specimens was governed by crack formation in the HAZ. Lower weld currents and weld times resulted in higher tensile shear properties. The highest tensile shear load (18.50 kN) and energy absorption (37.5 J) were achieved at 6 kA for 20 cycles. This weld exhibited interfacial failure mode.

Multi-response optimization of friction stir corner welding of dissimilar thickness AA5086 and AA6061 aluminum alloys by Taguchi grey relational analysis

Friction stir welding is a promising solid-state joining process to weld light materials like aluminum alloys. In this paper, an attempt has been made to optimize the friction stir corner welding process parameters using Taguchi grey relational analysis to attain the improved mechanical properties of dissimilar thickness AA5086 and AA6061 dissimilar aluminum alloys with plate thicknesses of 6 mm and 4 mm, respectively. The input parameters of the welding play a crucial role to achieve the desired weld properties. The friction stir welding experiments were conducted according to the L9 orthogonal array. The input process parameters are tool rotation speed (900–1100 r/min), welding speed (100–190 mm/min), and plunge depth (0.1–0.3 mm). The processes parameters were optimized and ranked based on the results of the grey relational analysis. The percentage contribution of each input process parameter on the weld quality was quantified using analysis of variance (ANOVA). The optimal process parameters were determined at tool rotation speed of 1100 r/min, welding speed of 150 mm/min, and tool plunge depth of 0.2 mm. The percentage contribution of the welding speed was 40.50% and revealed a significant influence on multiple responses followed by plunge depth 25.84% and rotational speed 18.13%. The microstructures of various regions were observed and analyzed. The fracture mode and fracture surface of the welded sample were observed and discussed.