To meet the demand for building light construction in moving vehicles or bridge construction, it is necessary to reduce the material usage and, or, material weight to reduce the environmental footprint, resulting in lower weight. A solution is to use Aluminium (Al) due to its excellent strength to weight ratio and properties such as high corrosion resistance. In construction, different classes of Al are used based on their variations of advantages. A challenge with this type of construction is when the Al classes are required to be welded together. To weld them together by fusion welding is complex compared to the welding of Steel. However, welding Al by Friction Stir Welding (FSW) it is possible to achieve a defect-free weld. Defects such as voids and cracks can be avoided. Both welding of non-heat treatable or heat treatable Al materials can be done by using FSW because the Al will not be melted but stay in the solid state.

The main aim was to achieve a defect-free weld of the dissimilar heat-treatable Al AA6082 and non-heat-treatable AA5083 by Friction Stir Welding (FSW), which is a more challenging than welding the same Al grades together. In addition, also get a better understanding of how the material placement effect the material mixing, hardness and how process parameters effect the weld quality and mixing. By altering the parameters rotational speed (1000-1300 rpm), downward force (3,5 kN-5,5 kN), welding speed (2,5 - 5 mm/s), and tool offset into Advancing Side (AS) (0- 2 mm). 

The samples were produced at PTC (Production Technology Centre), Trollhättan with an ABB six-axis robot with an FSW module. The tool had a convex shoulder (12 mm) with two scrolls and a crown pin (5 mm). Slower rotational speed (1200 rpm) and higher downward force (> 5 kN) gave the result of a defect-free weld with AA6082 placed at AS. The material placement strongly effects the material flow by the domination of AS material in the Thermo-Mechanically Affected Zone (TMAZ)-AS and Stir Zone (SZ) for both material placement, which was identified by the Vickers hardness test and Energy Dispersive Spectroscopy (EDS) analysis. Further, the weld was visible in the TMAZ/SZ after etching with Flick's reagent for 3 min.

Lighter areas were dominated by AA6082 and darker areas were dominated by AA5083. A higher hardness was seen in the areas dominated by AA5083 compared to the areas dominated by AA6082. The AA5083 needed a higher heat input to be welded compared to AA6082. Therefore, when AA5083 was placed at AS, it resulted in more problems with insufficient material mix and/or lack of heat input. The offsetting of the tool into AA5083 resulted in tunnel defects. To get a defect-free weld with AA5083 at AS, a larger shoulder diameter is recommended to increase the material mix and heat input.