Microstructure and texture correlation of secondary heating assisted dissimilar friction stir welds of aluminum alloys

Abstract

Present work aims to study the influence of secondary heating on material behavior during the friction stir welding (FSW) and examine it through the texture analysis. In the present context, the secondary heating pertains to the additional heat provided using a gas torch other than the heat primarily produced due to the process itself. Stop tool action technique is used to appraise the material flow around the pin. The material flow and evolution of textures during the process is studied by employing electron backscatter diffraction analysis. For analysis, the transverse sections of dissimilar FSW joints of AA6061-AA7075 and AA7075-AA2014 prepared with and without the application of secondary heating keeping the tool pin embedded in the joint are used. The basic assertions on strain rate based upon texture analysis and grain boundary engineering are used to explain the nature of material behavior during the process. The misorientation angle distribution is observed to shift towards random distribution for severe plastic deformation and additional heat supplied. Texture analysis reveals dominance of B/B‾ shear texture with sufficient C component in joints supplied with additional heating. For AA7075-AA2014 (without secondary heating) strong α-fiber is observed in the texture orientation distribution function plots. An equation is established to estimate the material volume flow around the pin in one revolution. The optical micrographs of welded joints prepared with and without use of secondary heating are compared to visualize the increase in material flow volume. The hardness of the joints obtained tend to decrease along the weld section on application of additional heat due to the dissolution of precipitates.