Papers by Keyword: Friction Stir Welding (FSW)

Abstract: A friction stir weld in 6005A-T6 aluminum alloy has been prepared and analyzed by micro-hardness measurements, tensile testing and scanning electron microscopy (SEM). The locations of the various weld zones were determined by micro-hardness indentation measurements. The flow behavior of the various zones of the weld was extracted using micro-tensile specimens cut out parallel to the welding direction. The measured material properties and weld topology were then introduced in a fully coupled micro-mechanical finite element model, accounting for nucleation and growth of voids as well as void shape evolution. The model shows satisfactory preliminary results in predicting the tensile behaviour of the weld and the true strain at fracture.

Abstract: In attempts to improve the performance of dissimilar joints between AZ31 Mg alloy and different Al alloys, solid state joining processes such as Magnetic Pulse Welding (MPW) and Friction Stir Welding (FSW) were applied for minimizing the formation of brittle intermetallic phases. MPW process has been concentrated mainly on round section tube to tube and tube to bar welds. Mg alloy AZ31 has been successfully welded to pure Al A1070 as well as to Al alloy A3003. Tensile test clearly showed the MPW welds were stronger than the weaker of the base metal so failure occurred in aluminum base metal. While FSW process for the dissimilar joint between AZ31B/A6061 alloys with a thickness of 2mm revealed optimum weldability under the conditions of travel speed of 0.8mm/sec and tool rotation speed of 850rpm. For the sound dissimilar joint, the maximum tensile strength of 179 MPa, which was about 80 % of the Mg base metal tensile strength, has been obtained.

Abstract: This paper presents the results of microstructural and mechanical characterization of Friction Stir Welding joints of two aluminum-based particles reinforced composites. The composites were FSW in the extruded and T6 heat treated condition. No post-weld heat treatment was carried out on the FSW joints. Hardness, tensile, low-cycle fatigue and impact tests were carried out. Microstructural and fractographic characterization were performed both on the base and FSW material, in order to investigate the effect of the solid-state welding process on the reinforcement particles and aluminum matrix. The FSW produced high quality joints with good microstructural characteristics: the welded zone displayed a refinement of the Al matrix grain size and reinforcement particles, and a better particle distribution. The FSW specimens showed high efficiency, both in the tensile, impact and fatigue tests.

Abstract: Friction stir welding (FSW) offers many potential benefits including reduced distortion, lower cost, no harmful airborne emissions, semi-automated, etc. Although initially developed for Al alloys, considerable work now has been completed to explore the ability of FSW to weld relatively thin (6 mm) ferrous alloys including many alloys of interest to the ship building industry such as HSLA-65. The status of current progress for ferrous alloys is presented offering insight into capabilities and opportunities as well as areas of FSW activity requiring additional improvement. Practical issues of weld penetration depth, gap tolerance, post-FSW mechanical properties, and distortion are addressed. Special consideration will be made to address the ability to friction stir weld 6 mm thick HSLA-65 steel with no/low distortion. Tool materials discussed will include polycrystalline cubic boron nitride (PCBN) and a new composite tool fabricated from PCBN and W-25Re. Last, data will be presented illustrating the complete absence of harmful airborne emissions when welding an austenitic stainless steel.

Abstract: The influence of short-term heat treatments on the environmental cracking and impact properties of a 7050-T7451 friction stir weld were investigated. Prisms, cut transverse to the welding direction, were exposed for minutes at temperatures between 100 oC and 800 oC in an oven or exposed to a propane torch flame and/or water / air quenched. A significant increase in the environmental cracking resistance (ductility ratio from 0.2 to 0.9) was observed for samples exposed to temperatures below the solutionizing limit, but between 240 oC and 280 oC. The fracture location changed from the “soft” heat affected zones to the nugget. Furthermore, the weld exhibited a decrease in the Charpy impact adsorbed energy as compared to the weld unaffected parent metal. An increase in the temperature improved the adsorbed energy, while a temperature decrease promoted the brittleness and reduced the adsorbed energy. The flow contours, also called onion ring bands, present within the nugget, represented a preferential fracture path during impact. The high temperature treatments followed by water quenching did not significantly improved the resistance to impact.

Abstract: This paper presents an experimental methodology to determine a Friction Stir Welding (FSW) means of production based on the experimental study of the tool / material mechanical interactions generated during the plunging and welding stages. These two stages have been identified as being characteristic for the qualification of a FSW equipment. This paper presents the experimental results of the parametric study done on the plunging and welding phases. Ranges of forces and torques diagrams were established according to the processing parameters, in order to qualify a means of production and select the process parameters allowing the operation on the available FSW equipment.

Abstract: The aim is to analyze a junction produced by a Friction Stir Welding (FSW) joining process under multiaxial loading, employing a modified Arcan test that allows an angle variation of the loading in order to evaluate the failure of the FSW weldment as compared to the base material. A short review of the earlier studies and relevant theories about the FSW processes and fracture modes I and II under multiaxial loading are presented and were experimentally evaluated for an AA2024-T3 aluminum alloy sheets (t = 1.6 mm) processed by FSW. The results obtained can serve as a basis to compare the junctions made using FSW and conventional joint methods such as rivets (very common practice in the aeronautical industry).

Abstract: Spot welding can be considered a very common joining technique in automotive and transportation industries as it permits to obtain effective lap-joints with short process times and what is more it is easily developed through robots and automated systems. Recently the Friction Stir Spot Welding (FSSW) process has been proposed as a natural evolution of the already known Friction Stir Welding (FSW) process, allowing to obtain sound spot joints that do not suffer from the insurgence of typical welding defects due to the fusion of the base material. In the paper, a modified Friction Stir Spot Welding (FSSW) process, with a spiral circular movement given to the tool after the sinking stage, is proposed. A continuum based numerical model for Friction Stir Spot Welding process is developed, that is 2D Lagrangian implicit, coupled, rigid-viscoplastic. This model is used to investigate the distribution of the main field variables, namely temperature, strain and strain rate, as well as the Zener-Hollomon parameter which, in turn, strongly affects the Continuous Dynamic Recrystallization (CDRX) process that takes place in the weld nugget. Numerical and experimental results are presented showing the effects of the process parameters on the joint performances and the mechanical effectiveness of the modified process.

Abstract: In the present study, the relationships between friction stir welding parameters and the tensile behavior of Al 2024-T4 joints was investigated. The aluminum alloy plates were butt-welded using a hardened steel tool with a threaded and fluted cylindrical pin at various tool rotation speed to advancing speed ratios. Metallographic observations, EDS analysis and microhardness measurements show that the band spacing in the periodic microstructure of the stir zone and the average microhardness of this region decrease with increasing speed ratio. Tensile ductility is strongly affected by welding parameters and final elongation increases significantly with speed ratio at the constant rotating speed of 900 rpm. This behavior is found to be associated with a change in tensile fracture location. Formation of microscopic voids at low speed ratios leads to premature fracture in the nugget zone, while in the defect-free joints produced at higher speed ratios the fracture location shifts into the HAZ on the retreating side, which exhibits the lowest microhardness value within the weld joint. At the optimum rotation speed of 900 rpm and speed ratio of 11.2 rev/mm the tensile strength and final elongation of the joints are equivalent to 97% and 77% that of base metal, respectively.

Abstract: Friction stir welding (FSW) is a fairly recent technique that utilizes a non-consumable rotating welding tool to generate frictional heat and plastic deformation at the welding location in the continuously-fed work piece. In the present investigation this welding process is applied to join 1050 cold-rolled aluminium plates. The effects of varying the welding parameters namely welding speed [56, 90 and 140 mm/min] and tool rotational speed [850 and 1070 rpm] on the mechanical and microstructural properties were studied. Vickers micro hardness results across the weldment showed that the weld nugget hardness is dependant upon the welding speed and the tool rotational speed. Increasing the welding speed at 850 rpm reduced the hardness at the weld nugget, whereas, at 1070 rpm the weld nugget hardness merely did not change. However, the hardness achieved at 850 rpm was constantly higher than that achieved with 1070 rpm irrespective to welding speeds. In the same fashion, the yield and ultimate strengths of the joints were influenced by varying the welding parameters. Increasing the welding speed at 850 rpm reduced both strengths whereas; at 1070 rpm they were almost unchanged. Microstructural study showed that the weld region is composed of unaffected base metal and the stir zoned [weld nugget] which is characterised by a fine equiaxed grain structure. Increasing the welding speed at constant tool rotational speed has caused a slight refinement in the weld nugget's grain size, whereas, decreasing the rotational speed has also led to weld nugget grain refinement.