Friction Stir Processing of AA6063-T6 Tubes and End Forming Characterization at Varying Tool Pin Profiles

Abstract

The effect of tool pin profiles on the end forming performance of friction stir processed (FSPed) Al6063-T6 tubes has been studied. FSP is done in the longitudinal direction of the tube. Straight cylindrical pin, tapered cylindrical pin, and stepped cylindrical pin (STP) are selected. End expansion, end reduction, and end beading experiments are conducted. The load-displacement curve and instabilities are evaluated and predicted by finite element simulations and the strain mapping method. The STP generates better ductility and a better strain hardening exponent because of the reduction in dislocation density in the stir zone. This has a considerable effect on load requirement and displacement at failure during end expansion and end beading, whereas it has an insignificant effect during end reduction. The hardness index of FSPed tubes improves during end forming because of strain hardening, which is appropriate for structural applications in industries. FSPed tubes perform equal to that of parent tubes in terms of energy absorption during end beading and end reduction, whereas it is not so in end expansion, highlighting the applicability of FSPed tubes for tube beading and reduction applications. Instabilities in the form of longitudinal crack, wrinkling, and overlap are observed. The predicted instability results agree well with experimental data during end reduction and end beading, and they have reasonable agreement during end expansion.