C. Leitão

High speed friction stir welding of aluminium alloys

Abstract In this paper, the weldability of AA 5083-H111 (non-heat treatable) and AA 6082-T6 (heat treatable) aluminium alloys, which are widely used in welding fabrication, is compared by analysing the welds obtained from both materials under a large range of welding conditions (varying tool dimensions, rotation and traverse speeds, axial loads and tilt angles) chosen to ensure high welding speeds. The differences in friction stir weldability, assessed by weld defect analysis and weld strength characterisation, will be related to the markedly different plastic behaviours of both base materials. Based on the experimental results, a methodology for determining suitable friction stir welding parameters is proposed.

Influence of weld geometry and mismatch on formability of aluminium tailor welded blanks: numerical and experimental analysis

Abstract The forming behaviour of tailor welded blanks (TWBs) has been widely studied since its development. In the numerical simulation studies, the TWBs are modelled as blanks composed of two different materials, and often, the presence of the weld bead is neglected in its finite element discretisation. In the present work, the influence of the weld bead shape on the formability of friction stir welded TWBs, is analysed. Several finite element meshes were constructed in order to represent different weld bead geometries and numerical simulations of the cylindrical cup drawing were performed. Strong influence of the weld bead shape on the formability of the TWBs was observed when the weld was in overmatch relatively to the base material, and little influence when the weld was in undermatch condition. Comparison of the numerical results with experimental ones shows that the numerical analysis is able to preview the formability of the TWBs.

Material flow in Friction Stir Welding

Friction stir welding (FSW) is a solid-state joining technique initially developed for aluminium alloys. The heat generated by a rotating tool softens the material in the vicinity of the tool. The material undergoes intense plastic deformation following quite complex paths around the tool, depending on the tool geometry, process parameters and material to be welded [1, 2]. The comprehension of the material flow is essential to prevent voids and other internal defects which may form during welding [3]. Several techniques have been used for tracking material flow during FSW such as metallography, the use of a marker material as a tracer or the flow visualization by FSW of dissimilar materials or even the X-ray and computer tomography [4, 5]. Some of these techniques are useless in the analysis of welds in homogenous materials or welds between materials of the same group. The aim of this investigation is tracking the material flow in FSW between 1mm thick sheets in aluminium alloys AA 5182-H111 and AA 6016-T4, currently used in automotive industry.

Friction Stir Welding of very thin plates

The results obtained in present research, relative to friction stir welding of 1 mm thick plates of aluminium, copper, copper-zinc and zinc alloys, prove that the application of the process in the joining of very thin plates is feasible and desirable. In fact, independently of the base material, the welds produced presented very good morphological characteristics and significant grain refinement in the nugget. Tensile and hardness tests proved that all the welds were at least in even-match relative to the base material properties. Based on the AA 5182 aluminium alloy results it was also possible to conclude that augmenting the welding speed, which improves process productivity, increases grain refinement in the nugget, improving the mechanical properties of the welds.

Analysis of weld defects in similar and dissimilar resistance seam welding of aluminium, zinc and galvanised steel

Abstract In the present investigation, a microstructural characterisation of welds performed by resistance seam welding was carried out, with special focus on weld defect analysis. In order to perform a comparative weldability analysis, the welds were performed using similar welding procedures. Similar welds in aluminium (5754-H22) and zinc (Zintek) alloys, as well as dissimilar welds between galvanised steel and zinc, were studied. The defective aluminium welds were found to be characterised by important grain growth inside an inhomogeneous nugget and by the presence of important voids and cracks. The zinc welds showed a well defined nugget, but with porosities and some cracks. In the dissimilar steel–zinc welds, important macroscopic defects were observed. Microstructural analysis evidenced the occurrence of melting at the zinc side of the welds; meanwhile, no microstructural modifications could be observed for the steel side. Defect formation, as well as weld morphologies, was related to the variation in welding parameters.

Microstructure and Hardness of Friction Stir Welds in Pure Copper

The aim of present research was to study the effect of the position of the tool relative to the support backing plate of the FSW machine on the formation of defects and on alterations of the microstructure and mechanical properties of friction stir welds in phosphorus-deoxidised copper (Cu-DHP) thin sheets of 1 mm thick. The welds were carried out using position control conditions; distances between the tool and the backing plate of 0.1 mm, 0.075 mm and 0.05 mm were used. The formation of defects like continuous voids along the weld is very influenced by the tool position, though the heat-input plays an important role in the process. Large grain refinement was observed in the nugget of the welds; the change of the relative tool position has little effect on this grain refinement. Substantial hardening was observed in the thermomechanically affected zone (TMAZ) of the welds. The welds exempt of defects, such as continuous voids, attained a little tensile strength overmatch condition.

Friction stir welding industrialisation and research status

ABSTRACT This paper intends to provide a perspective on the current development of the friction stir welding (FSW) technology. The industrialisation of the technology and related research were assessed by analysing patent and scientific publications databases. The literature reviews on FSW and related technologies were also collected and analysed. The work performed enabled to understand the main areas of industry/research where the FSW technology is being applied/explored and the geographical distribution of the main players in its implementation/research. The main FSW process variants, the materials already welded/processed using it, as well as the applications envisaged, were also analysed. The data collected shows that the FSW technology, originally developed for the joining of light alloys, became a research tool with interest in several fields of engineering and material science.

Taguchi Analysis of the Effect of Process Parameters in Friction Stir Welding

The task of obtaining suitable welding parameters for the friction stir welding process is often a difficult one, due to the lack of published data and the fact that the exact mechanism by which the process operates has not yet been fully determined. Therefore, suitable welding parameters often need to be obtained by using extensive, time consuming and expensive experimental methods. The work detailed in this paper pertains to the use of the Taguchi method as a mean to reduce the disadvantages of these experimental methods, more specifically, their cost. The Taguchi method accomplishes this task by substantially reducing the number of welding trials that are needed to obtain suitable welding parameters. This reduction leads to the parameters being obtained more rapidly and at a substantially smaller cost. In this paper a procedure for applying the Taguchi method to the friction stir welding process is presented as well as its application to the welding of a specific component. The method was applied to the welding of 4mm thick AA5083-H111 plates in a butt joint configuration, which constitutes one of the most common industrial welding scenarios. The purpose of the experimental tests was to maximize the welding speed whilst ensuring an acceptable welding quality. The quality of the welds was determined through visual inspection and tensile and bending tests. The application of the Taguchi method allowed, with a relatively small number of experimental welds, to provide some insight into the manner by which the parameters should be altered in order to optimize the process.

The Relation between the Plunge Pressure and the Mechanical Properties of Friction Stir Welded 3mm Thick AA6082-T651 Sheets

Friction Stir Welding (FSW) is a relatively young technology in the field of welding. Its process parameters and their influence on weld quality are currently the topic of intense research. Present work focuses on the influence of the tool plunging force on the mechanical properties, microstructure and surface finish of friction stir welds. Three welds have been produced using the same tool rotation and traverse speed and different tool dimensions and plunging forces. Visual inspection, optical and scanning electron microscopy were undertaken to assess surface and dimensional features as well as to study microstructure. Bend, hardness and tensile tests were carried out to characterise the weld strength. Taken into account the plunging force values of the conducted welds, a relationship between weld properties and calculated welding pressures was created. Favourable welding pressure values are recommended.

Influence of the structure and phase composition of the bond interface on aluminium–copper lap welds strength

ABSTRACT The structure and phase composition of the bond interface of aluminium–copper lap welds produced by friction stir welding and tool-assisted friction welding were analysed. Microstructural analysis proved that no through-interface material flow took place in tool-assisted friction welding and that aluminium–copper joining resulted from the formation of a thin and continuous intermetallic layer at the lap interface. For the welds produced by friction stir welding, evidences of through-interface material flow were found, promoting mechanical interlocking of both base materials, at the lap interface, and formation of discontinuous intermetallic layers. Mechanical testing showed that the tool-assisted friction welds, with excellent surface finishing, had low strength, contrary to the friction stir welds, which displayed excellent bond strength. The comparison of the mechanical and microstructural results, for both weld types, pointed to the ineffectiveness of the continuous intermetallic layer in providing high strength bonding.