Formability of tailor welded blanks produced by friction stir welding - a study on the effect of tool pin profile and eccentricity

Abstract

The manufacturing of multi-material components in the form of Tailor welded blanks (TWBs) has been identi ed as a promising design strategy to achieve weight reduction of the sheet metal parts. The low formability of aluminium TWBs made by conventional welding techniques is a major concern for such ap- plications. Friction Stir Welding (FSW) can be e ciently used for the production of aluminium TWBs with superior forming properties. In this work, Al 5052 alloy sheets of 2mm thickness have been welded using FSW. Three levels of rotation speeds and four tool pin pro les (tapered, square, and both tapered and square with eccentricity or axis o set) were used for joining of sheets. The formability of the welded sheets has been assessed using limiting dome height test and compared with the base metal. The mechanical characterization has also been done using uniaxial testing, hardness pro le and roughness pro le. A signi cant improve- ment in the tensile strength, ductility and formability was found as compared to the base metal. Forming limit diagram is a useful measure of the formability of sheet metals. The LDH test was carried out only in the plane strain and biaxial stretching conditions to determine the limit strains. However, a total of six strain paths were considered to generate the full FLD using nite element code PAM STAMP 2015. The properties of the weld zone were determined by taking out longitudinal tensile sample from the weld zone only. The material properties re- quired for simulation such as strain hardening exponent, plastic anisotropy, yield strength etc. were determined from tensile tests. The material ow pro le in the weld zone for di erent pin geometries were also compared using macro-structural images. It was found that the pin pro le has more in uence on mechanical proper-ties at higher tool rotation speeds. The change in overall heat input and material ow behaviour due to variation in tool pin pro le was mainly responsible for such di erence in properties. In the nite element simulation, the initiation of localized necking was identi ed using di erent necking criterion and a close match with the experimental results was obtained.