Mechanical properties of friction stir welded 5083-h321 and 6082-t651 dissimilar aluminium alloys

Abstract

Friction stir welding (FSW) is the fastest growing joining technique and the major prospective method of producing reliable welded components in a more efficient environmentally friendly manner. FSW relies on repeatability, integrity and easy of producing components that were impossible to produce before. This method is underpinned by the use of non-consumable tool, easy use of parameters to set for constant production and attainable tool geometries. The aim of this project was to investigate mechanical properties of Friction Stir Welded 5083-H321 and 6082-T651 dissimilar aluminium alloys. Tool steel H13 tri-flat threaded tool was used with tool rotational speed of 800rpm and traverse speed of 60mm/min on a 6mm thick plates. Plates were FS welded whereby 5083-H321 was placed on the advancing side and 6082-T651 on the retreating side and the plates were changed vice versa with the speeds kept unchanged. Specimen were extracted from different locations of FS welded joints being the start, middle and the end of the weld and the effect thereof was studied on the tensile strength, bending strength, microhardness, macrostructure, microstructure and scanning electron microscope. All the extracted specimens were compared to parent materials. Plates were FS welded successfully with no surface voids observed on visual inspection and on internal metallurgical structures. Macrostructure showed similar patterns for advancing, retreating and locations of specimen regarding the orientation and nature of TMAZ, HAZ and SZ. However, the microstructures revealed more homogenous mixture of SZ when 5083-H321 was retreating. Grain sizes when 6082-T651 was advancing were bigger than when 5083-H321 was advancing though there was no positional significance noted. Average micro-hardness values were found to be better when 6082-T651 was advancing. The average size of micro-hardness values for 6082-T651 was 70HV while 5083-H321 was 60HV. Tensile tests specimens broke on 6082-T651 HAZ for all the specimens. The 5083-H321 on advancing side had better UTS though 6082-T651 on advancing showed higher elongations. In bending tests, parent materials managed to achieve 180°bend without signs of cracks while the welded joints managed 90°bend and started cracking on the root welds along the butt interface. Bending tests proved to have better strength than tensile tests for both parent materials and welded joints. Scanning electron microscope (SEM) fractograph was characterised by ductile dimples, micro-voids and shearing during tensile testing. The study was found to be in congruence with most previous findings in many aspects. The only contradiction observed was the nugget pointing towards the advancing side when the 6082-T651 was on the retreating side, this was contrary to the most studies reviewed.