S. Muthukumaran

Comparison of microstructure and mechanical properties of conventional and refilled friction stir spot welds in AA 6061-T6 using filler plate

Friction stir spot welding with refilling by friction forming process (FSSW-FFP) was successfully modified using filler plate. Both of this new refilling technique and conventional friction stir spot welding (FSSW) process were used to weld Al 6061-T6 lap shear specimens and the results were compared. Effects of tool rotational speeds on mechanical and metallurgical properties in both the cases were studied. Static shear strength of refilled weld samples was found to be better than those welded by conventional FSSW process at all tool rotational speeds. This is explained in terms of effective increase in cross-sectional area of weld nugget due to addition of more material from filler plate, thereby eliminating the probe hole. Failure mechanisms were discussed and fracture surfaces were analyzed through scanning electron microscopy (SEM). The hardness profile of the welds exhibited a W-shaped appearance in both the processes and the minimum hardness was measured in the HAZ.

Refilling Probe Hole of Friction Spot Joints by Friction Forming

Friction stir spot welding (FSSpW) is a variant of friction stir welding (FSW) that has wider industrial application. However, Probe hole left after the welding is the main limitation of their process. In this present study, modified FSSpW has been developed and the refilling is achieved by friction forming process. This process has been called Friction Stir Spot Welding with refilling by Friction Forming Process (FSSpW-FFP). The Aluminum alloy (AA 6061-T6) plates are welded in two stages. Welding and refilling are achieved in first and second stages, respectively. Mechanical and metallurgical properties of the joints are studied and compared with welds made by FSSpW. The mechanical properties studied in the present work are tensile shear strength and microhardness. Macro- and microstructures of weld joints are compared and analyzed. The mechanical and metallurgical properties of the joints made by FSSpW-FFP are found to be better than the joints made by FSSpW. The tensile shear strength of the joint with refilled hole is higher than that of the joint with probe hole. The refilling process increases effective cross-sectional area of the nugget, resulting in higher tensile shear strength and joint efficiency at medium and high tool rotational speeds. After experiment, fracture surfaces are analyzed in detail using scanning electron microscope (SEM). The pull out of the nugget, i.e., plug type fracture, occurs in the joint with refilled probe hole, while shear fracture through the nugget is observed in the joint with probe hole.

Effect of tube preparations on joint strength in friction welding of tube-to-tube plate using an external tool process

Several developments have been occurring in the field of materials processing, and friction welding is an important metal-joining process that has varied industrial applications. Friction welding of tube-to-tube plate using an external tool (FWTPET) is a vital friction welding process which is capable of producing leakproof high-quality weld joints. In the present study, FWTPET welds have been prepared with five different tube preparations. Liquid penetrant test (LPT) has been conducted in order to detect the occurrence of surface defects. Macro- and microstructural studies have been conducted and they reveal that improper weld configuration is susceptible to defect formation. Besides, hardness and tensile strength of five different tube preparations have been presented and analyzed. The present study leads to the production of defect free weld joints which have numerous industrial applications.

Influence of Water Cooling and Post-Weld Ageing on Mechanical and Microstructural Properties of the Friction-Stir Welded 6061 Aluminium Alloy Joints

A 6061-T6 aluminium alloy was friction stir welded in submerged water as well as in air cool at a constant traverse speed and different rotational speed in order to investigate the microstructural characterization and mechanical behaviour of the joints. In order to improve the tensile strength of the joints, weldments were studied at different heat treatment processes such as post weld aged condition and solutionized condition. It is observed that, water cooled joints are resulted in enhancing of both strength and ductility with the lower strain hardening ability than the air cooled joints. The width of the hardness distribution varies with the different cooling process of the joints. The highest hardness peak observed to be located in the heat affected zone of the joints. The maximum tensile strength of the joints achieved for welds under water cooled conditions in contrast to air cooled conditions. Moreover, a combination of water cooling and post weld ageing is proven to be the optimal path to improving the microstructural and mechanical properties of the joints with a maximum efficiency of 89.87% of the base metal strength. The microstructural observations of the joints revealed the presence of voids defects for the low rotational speed joints due to the insufficient heat input. The nugget of the higher tensile strength joints were free from defects and showed the fine grained material flow patterns which are constructive to obtain better mechanical properties.

Eco-friendly aspects associated with friction welding of tube-to-tube plate using an external tool process

The competitiveness among the manufacturers has been forcing the manufacturing processes to be eco-friendly so as to deliver products with lesser impact on the environment, energy demand and other resources consumption. In this regard, this article presents the unique environmentally friendlier aspects associated with an innovative welding process namely friction welding of tube-to-tube plate using an external tool (FWTPET). This process is capable of generating robust weld joints with lesser energy consumption. A comparative analysis of FWTPET with conventional tungsten inert gas welding process has been narrated.

Static shear strength and fatigue life of refill friction stir spot welded AA 6061-T6 sheets

Abstract This study was aimed at evaluating the static shear strength and fatigue properties of the newly developed refilled friction stir spot welded AA 6061-T6 joints. The keyhole, the process disadvantage of conventional friction stir spot welding, was refilled successfully, using an additional filler plate, with specially designed tools. Two different tool profiles, namely, convex and concave, were used for the refilling process. Sound and defect free joints were obtained by the refilling process. Joints refilled with convex tools showed better static shear strength than those with the concave ones. The variation of microhardness in different regions of the weld was analysed. Fatigue tests were conducted on the lap shear specimens at a stress ratio of R = 0·1. The optical micrographs of the welds after fatigue failure in both the conventional and refilled processes were examined to study the fatigue crack propagation and failure modes.

Interfacial Microstructure and Strength of Friction Welding of Steel Tube to Aluminium Tube Plate using an External Tool

Joining of dissimilar materials is of increasing interest for a wide range of industrial applications like nuclear, thermal power. The automotive industry, in particular, views dissimilar materials joining as a gateway for the implementation of lightweight materials. Friction welding of tube to tube plate using an external tool is an innovative friction welding process and is capable of producing high quality leak proof weld joints. In the present study, friction welding of steel tube to commercial aluminum tube plate using an external tool with and without tube projection have been performed. The joints were evaluated by mechanical testing and metallurgical analysis. The results of bonding interface hardness and joint strength reveal that steel tube with projection are better than the steel tube without projection.

Suitability of friction welding of tube to tube plate using an external tool process for different tube diameters—A study

During the past few decades, the field of welding technology has been witnessing tremendous challenges. Welding is an important metal fabrication process that has high potential for industrial applications. Friction welding is a vital solid state joining process that has gained popularity in welding non-weldable alloys. Friction welding of tube to tube plate using an external tool (FWTPET) is an innovative friction welding process and it was invented in the year 2006. FWTPET is capable of welding tube to tube plate of similar or dissimilar metals and is capable of producing good-quality leak-proof weld joints. In this work, four different tube diameter conditions in FWTPET welding have been studied. Macrostructural and microstructural studies have been conducted and they reveal the weld configuration that is susceptible to defect formation. Hardness and tensile strength of four different tube diameter preparations have been analyzed. The present study leads to the production of defect-free weld joints which have numerous industrial applications.

Subshoulder formation during friction stir welding of steel using tungsten alloy tool

Abstract A study was carried out on the friction stir welding of low alloy steel plates, to understand the influence of the tool profile on the tool wear rate, using a tungsten alloy tool. Three tool profiles were used for the wear study, namely, tool A with a concave shoulder and tapered pin of 2·8 mm, tool B with a flat shoulder and tapered pin of 2·6 mm and tool C with a concave shoulder and tapered pin of 2·6 mm. The tool wear characteristic was analysed by three methods, namely, the profile projector, weight loss and the image processing technique, and it was found that tool C gave reduced tool wear, when compared to the other tool profiles. In tool C, an impression of a step-like formation was generated automatically in the pin during welding and named as a subshoulder, which proved to be the optimised design.

Influence of flash trap profiles on joint properties of friction welded CP-Ti tube to 304L stainless steel tube plate using external tool

Abstract Titanium tube and stainless steel tube plate were welded by an innovative friction welding of tube to tube plate using an external tool (FWTPET). Copper was used as an interlayer for joining the dissimilar materials and also to minimize the effect of intermetallics formed at the joint interface. The process parameters that govern FWTPET process are plunge rate, rotational speed, plunge depth, axial load and flash trap profile. Among them, the flash trap profile of the tube has a significant influence on the joint integrity. Various flash trap profiles like vertical slots, holes, zig-zag holes, and petals were made on the titanium tube welded to the stainless steel tube plate. Macroscopic and microscopic studies reveal defect-free joints. The presence of copper interlayer and intermetallics was evident from X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The microhardness survey was presented across and along the interface. A novel test procedure called “plunge shear test” was developed to evaluate the joint properties of the welded joints. The highest shear fracture load of 31.58 kN was observed on the sample having petals as flash trap profile. The sheared surfaces were further characterized using SEM for fractography.