Abstract
Friction Stir Welding (FSW) is regarded as the most significant development in joining over the past two decades. In FSW, process parameters and tool geometry play a fundamental role in obtaining desirable mechanical properties and microstructures in the welded zone. The tool geometry plays an important role in producing sound friction stir welds. Tool designs are however, generally propriety to individual researchers and only limited information is available in open literature. There are however, continuous efforts to understand the material flow and the influence that the FSW tool design has on the friction stir welded material. Within industries that use various welding techniques it well known that FSW is particularly suited for the welding of aluminium; there is great potential for FSW of copper. Given the limited supply, high cost, copper theft and commercial demand associated with copper, engineers and scientists will either attempt to reduce the quantity of copper consumed by industries or alternatively replace copper with a substitute metal that exhibits similar attributable properties. On account of the limited supply and consequently the high cost associated with copper and copper alloys; the need to join aluminium and copper and its’ alloys is anticipated to increase in the near future. FSW of dissimilar alloys/metals has attracted extensive research interest due to potential engineering prominence and inherent problems associated with conventional welding methods.
This research identifies the choice of suitable tool designs and process parameters to produce sound dissimilar friction stir welds of 5754 aluminium and C11000 copper. This research focuses primarily on determining the effect of FSW process parameters on the forces experienced by the FSW tool and the relationship that this has on the electrical conductivity properties of the friction stir dissimilar weld.
The experimental work was performed by completing dissimilar friction stir welds on 3 mm thick butt welds of the two materials by means of an I-stir FSW platform. During the experimental work, the rotational speed was varied between 600 and 1200 rpm in intervals on 300 related to low, medium and high rotational speeds respectively and four different FSW tool geometries were tested. The first tool was a new design with a unique shoulder topography and a cylindrical pin named the “Reddy tool”. The second tool was a tool consisted of a concave shoulder and conical pin. Tests were performed using the second tool at a 0 degree tilt and at a 2 degree tilt relative to the work-piece. The third tool consisted of a concave shoulder and cylindrical pin. The forth tool design consisted of a flat shoulder and a cylindrical pin.
This research forms part of the initial experimental work to determine the forces and electrical resistance of dissimilar friction stir welds of aluminium and copper by employing different tool shoulder designs. The welds were characterised through visual inspection, weld defect and material flow analysis, microstructural evaluation, electrical resistance measurements and tool forces and tool torque analysis.
Microstructural evaluation results revealed complex flow patterns of copper and aluminium material. Lamellae structures composed of copper particles with a streamline shape and continuous aluminium strips were present. Some evidence of dynamic recrystallization was observed in the nugget of the defect free welds. Based on material flow evaluation and defect formation results, the Reddy tool design is most suitable for high and low rotational speeds, the conical Shoulder tool at no tilt is most suitable for medium rotational speeds, the conical shoulder tool at a two degree tool tilt is most suitable for medium rotational speeds, the...
M.Ing. (Mechanical Engineering)