A different attempt to improve the formability of aluminum tailor welded blanks (TWB) produced by the FSW

Tailor welded blanks (TWBs) are produced by welding blanks with different characteristics as such thickness and/or coating and/or material, etc. The forming characteristics of a TWB are different from typical sheets, as TWB is a combined blank each section has its own forming behavior. The current investigation aims to analyze the formability characteristics of TWBs made by joining AA6061 aluminum alloy sheets with different thicknesses. The sheets were joined by friction stir welding (FSW) and also by an improved FSW entitled friction stir vibration welding (FSVW) method at different welding speeds, rotational speeds, and tool tilt angles. The Taguchi method was used for the design of experiments and mean analysis was applied to find the optimum values of welding processes. ANOVA was applied to find the effect of the welding processes on formability. The formability of the TWBs has been assessed with the help of the limiting dome height (LDH) criterion. According to optical microscopy (OM) and electron backscatter diffraction (EBSD) analyses, grains in the stir zone of FSVW-ed blanks were smaller than those in FSW-ed blanks. It was shown that based on the Frank-Read dislocation mechanism, the density of dislocations increased as vibration used during FSW. From the results, it was concluded that the mechanical and formability behaviors of FSVW-ed blanks were higher than those of the FSW-ed blanks. It was also obtained that for the welding speed range studied in the current research, formability and mechanical behaviors of TWBs increased as welding speed increased.