The effect of FSP conditions towards microstructure and mechanical properties of the AA6082/AA8011 TIG-welded joint

Abstract

The friction stir processing (FSP) technique was employed on the AA6082-AA8011 TIG-welded joints to investigate the contribution of the processing conditions on the microstructure and mechanical properties of the processed joints. The TIG-welded joints were subjected to the FSP technique under normal and submerged conditions. The tests conducted included microstructural analysis, tensile, Vickers hardness and fracture surface analysis. The microstructural analysis of the normal FSP joints showed the minimum average grain size of 7.83 μm and maximum average of 9.25 μm, while the submerged FSP joints had a range of 6.33 μm to 4.86 μm. All the FSPed joints showed a great grain size refinement compared to the TIG-welded joints which had an average grain size range of 25.71 μm to 21.99 μm. The ultimate tensile strength (UTS) of the joints processed under normal conditions ranged between 87.14 MPa and 88.33 MPa while that of the submerged conditions ranged between 88.79 MPa and 91.56 MPa. The elongation range of the normal FSP joints was 22.71% to 24.28% while 24.08% to 28.81% was obtained from the submerged FSP joints. The TIG-welded joints had a UTS range of 80.27 MPa to 85.36 MPa with an elongation of 21.82% to 23.58% respectively. FSP improved both the tensile strength and the ductility of the joints with the submerged conditions giving best improved results. The fracture surface morphology revealed a ductile failure mode for all the specimens. The TIG-welded joints had a maximum hardness range of 56 HV to 60 HV, while that of the normal and submerged FSP joints ranged between 54 HV and 57 HV, and between 60 HV and 65 HV, respectively. The application of Normal FSP on the TIG welded joints slightly compromised the hardness of the joints under normal conditions but improved under SFSP due to rapid cooling.