The impact of material positioning towards the friction stir welded dissimilar aluminium alloy joints

Abstract

Background: Friction stir welding is an advanced process that could be used to join dissimilar materials and alloys. However, there are some areas that require some further analysis. This involves the impact of the material positioning on various dissimilar joints. Objective: The purpose of this paper is to investigate the influence of material positioning on the microstructure and the mechanical properties of AA8011/AA6082 and AA6082/AA8011 dissimilar joints. Methods: The materials used in this study were the 6mm thick AA8011 and AA6082-T6 plates. The welding conditions include a tool rotational speed of 1100 rpm, and a traverse speed of 60 mm/min. Microstructural analysis, Vickers hardness and tensile tests were conducted in order to be able to draw a comparison between the respective joints. Results: The joints (AA8011/AA6082 and AA6082/AA8011) both experienced dynamic recrystallization. The positioning of the stronger strength alloy on the advancing side resulted in finer microstructural grains compared to when the lower strength alloy was positioned on the advancing side. The maximum stir zone hardness of 75 HV was obtained on the AA8011/AA6082 dissimilar joint, while the AA6082/AA8011 had a minimum hardness of 68 HV. Both hardness values were lower than the AA6082 hardness but greater than that of the AA8011. The positioning of AA6082 on the advancing side resulted in higher ultimate tensile strength than when AA8011 was on the advancing side. The AA6082/AA8011 joint was found to be more ductile in comparison to the AA8011/AA6082 joint. The fracture surface morphology of the post tensile specimens also revealed a ductile failure morphology. Conclusion: Placing the stronger strength alloy on the advancing side resulted in valid overall results of the tests conducted.