Effect of pre-strain path on suppression of abnormal grain growth in friction-stir welded 6061 aluminum alloy

Abstract

In this work, an efficiency of various pre-strain paths for suppression of abnormal grain growth in friction-stir welded 6061-T6 aluminum alloy was studied. To this end, the produced welds were cold rolled at either 0°, 45° or 90° to welding direction prior to the standard T6 tempering. A particular emphasis was given to elucidation of a relationship between microstructures and ductility of the post-processed welds.In all cases, the pre-strain rolling was found to be effective for inhibition of the abnormal grain growth. At relatively low rolling strains, this effect was sensitive to the strain path. Specifically, the pre-rolling along the welding direction resulted in the finest grain structure in the heat-treated joints. This result was attributed to relatively high Taylor factor as well as to low orientation stability of the stir zone texture for this particular rolling path, which enhanced recrystallization behavior during subsequent annealing.Tensile behavior of the heat-treated welds was shown to be dictated by strain localization in coarse-grained microstructural regions. It was established that appropriate microstructural control by the pre-strain rolling can provide a reasonably uniform microstructure distribution across the weld zone and thus essentially enhance weld ductility.