Affected Zones in an Aluminum Alloy Frictionally Penetrated by a Blind Rivet

Friction stir blind riveting (FSBR), taking the advantages of friction stir processing with blind riveting, is a new joining process for dissimilar materials. This work is the first to employ electron-backscattered diffraction (EBSD) techniques to examine the microstructural evolution in an aluminum alloy sheet (AA6111), which was frictionally penetrated by a rotating blind rivet. The purpose of this work was to develop a basis of microstructural understanding for subsequent investigations into thermal-mechanical modeling and/or mechanical behavior of the joint. Specifically, EBSD observations and microhardness results are identified and helped to characterize in the area close to the blind rivet; a stir zone (SZ), three thermomechanical-affected zones (TMAZs), as well as a heat-affected zone (HAZ). In the TMAZs, the microhardness decreased from above to below that of the base material as the distance to the rivet increased, and the HAZ was softer than the base metal. Fine (∼ 1 μm) and low aspect ratio grains were characterized in the SZ, and grain size increased as the distance to the rivet increased within the TMAZs. Nearly, no difference was observed in the grain structure between the HAZ and the base material.