Friction Stir Spot Welding Technique Research Articles

Analysis of Mechanical Properties and Microstructure of Aluminum and Copper Sheet Welding Using Friction Stir Spot Welding Method

Welding aluminum and copper materials using friction stir spot welding (FSSW) is widely practiced. Although strong enough, it still produces keyhole and shoulder marks, which are quite large due to the large shoulder and pin sizes. This study investigates the joining of aluminum and copper panels using the FSSW technique using smaller shoulders and pins in different shoulder shapes. The study began by cutting aluminum and copper panels 150 mm long, 50 mm wide, and 5 mm thick. The joining process was carried out at rotational speeds of 900, 1200, and 1500 rpm with tools with several variations in pin length. Pin lengths of 0, 5, and 7 mm with pin diameters made the same at 5 mm, shoulder diameter 20 mm. The connection was observed for macrostructure, microstructure, and hardness. Different tool geometries have the potential to be applied in FSSW joints, especially for sheets. The highest hardness value is found in Cu-Cu material welding, with an average hardness value of 101.63 HVN in the stir zone area. The lowest hardness value is located in the base metal of aluminum material, with an average hardness value of 48.37 HVN.

Investigation of welding defects in friction stir spot welding of plastics

In friction stir spot welding applications, there are some factors that provide welding strength, welding performance and the formation of defects that may occur in welding. Among these factors, machine parameters and welding tool design should be compatible with each other. If these factors are not chosen appropriately, the welding will not be of the desired quality. In this study, high density polyethylene sheets were joined using friction stir spot welding technique. It has been determined that some of the joints made have low weld strength, defects on the weld surface and around the stir zone. By investigating the causes of these defects, suggestions were made to prevent these defecs It has been observed that these defects are not repeated in the welds made with the suggestions made and it has been determined that high weld strength can be obtained. The highest weld strength and performance were obtained by 0.2–0.4 mm plunge depth, 45–60 s stirring time, 700–900 tool rotation speed and 30 mm shoulder diameters. In order to obtain a perfect weld in friction stir spot welding, it was determined that a homogeneous mixture should be formed between the stirring zone and the thermo-mechanically affected zone. Low weld strength was obtained in all joints with defects detected in these regions. Low weld strengths and weld defects were detected at dwell times of less than 30 s, at all tool rotational speeds with a stirring time of less than 45 s, at a plunge depth greater than 0.4 mm, and at low tool rotation speeds.

Application of Friction Stir Spot Welding on Additive Manufactured Carbon Fiber Composite

Friction stir spot welding as a solid state processing technique is used to join dissimilar and similar metals, composites and polymers. This study illustrates the implementation of friction stir spot welding (FSSW) on additive manufactured nylon-based composites with chopped carbon fibre reinforcements. The purpose of this study is to employ FSSW technique for joining additive manufactured carbon fibre composites. The utilization of pinless tool serves a crucial function in the formation of sound welded joints. The joining process consists of two mechanisms: the piercing and melting of the sheets and the adhesive bonding during the re-solidification. As a result of the FSSW process, the joints indicate a decent mechanical performance with a lap shear failure force (LSFF) of about 250N.

Characterizations of AA5083-H116 produced by friction stir spot welding technique

ABSTRACT This research investigates the influence of friction stir spot welding (FSSW) process parameters on friction stir spot welded aluminium 5083-H116 alloy properties. Various characterisation techniques were applied such as optical microscope and scanning electron microscope, the microhardness profile was used to determine the hardness profile, while X-ray diffraction (XRD) was used to determine the phase formation. The electrochemical potentiodynamic polarisation technique was utilised to determine the corrosion behaviour. Based on the findings obtained, the process parameters were found to play a significant role in the microstructural evolution. It was established that the structural, mechanical, corrosion and metallurgical properties were significantly improved compared to the base metal in this research work. It was revealed that the lowest corrosion rate was obtained at a rotational speed of 900 rpm and dwell time of 15 s, respectively. It was also revealed that the welded samples crystallinity was improved from the XRD analysis compared to the base metal. The highest hardness profile was obtained at the stir zone of the welded area. The highest hardness value was achieved at the stir zone of the sample produced at a rotational speed of 900 rpm with an average hardness value of 112.62 HV.

Friction stir welding and friction stir spot welding of polymethyl methacrylate (PMMA) to other materials: A review

Polymers are widely used in packaging and automobile industries because of their desirable properties such as lightweight, transparency, strength to weight ratio, good hardness and stiffness, low water absorption, ultraviolet rays' protection. Keeping Polymethyl methacrylate (PMMA) polymer in focus, this review research is being done here to collect the literature available best of our knowledge on the joining of PMMA to PMMA/Polymers/ Metal alloys by Friction stir welding/ Friction stir spot welding (FSW/FSSW). Friction stir welding is a solid-state joining process in which the temperature remains below the material's melting temperature. This friction stir welding technique is widely applied on materials that are difficult to weld by fusion welding, such as aluminium alloys, titanium alloys, and polymers. Friction stir welding is an ecological weld method and environmentally friendly as it does not produce harmful radiation toxic gases, requires less energy, produces less waste than conventional fusion welding processes. It was found out that by applying Friction stir welding/ Friction stir spot welding technique, the Polymethyl methacrylate can be welded to itself, to polymers, and metal alloys. In this review, efforts are made to point out the optimum level of process parameters of FSW concluded by researchers in their studies of PMMA joining. For each study, its parameter range and the optimum value of process parameters are presented in the form of tables and graphs, and explanations and discussions are made to better understand welding Polymethyl methacrylate polymer by Friction stir welding process.

Characterization of Polypropylene Sheet Friction Stir Spot Welded Joint

A study to determine the effect of rotational speed and geometric shape of a tool on the mechanical properties of polypropylene joint using the FSSW technique has been carried out. A polypropylene sheet was cut into pieces with a dimension of 150 x 30 x 5 mm. A medium carbon steel bar was machined to fabricate welding tools. Two types of devices with shoulder angles of 0° and 5° were prepared, while the other parametric geometries were the same. While the friction stir spot welding (FSSW) process has been carried out at variations of rotational speeds of 985, 1660, and 2350 rpm, the other welding process parameters, such as tool plunge rate, dwell time, and delay time, were considered constant. The tensile shear load capacity, macrostructure, hardness, and failure mode of the joint results were then evaluated. The results revealed that using a pin tool with a shoulder angle of 5° achieved a maximum tensile shear load capacity at a rotational speed of 2350 rpm with a result of 2253 N due to its wider nugget area. The load capacity increased with the increase of rotational speed. A pin tool angle of 15° with a shoulder angle of 5° may be suggested for the tool’s chosen geometry.

Influence of Refill Friction Stir Spot Welding Technique on the Mechanical Properties and Microstructure of Aluminum AA5052 and AA6061-T3

This paper presents the effects of using the refill friction stir spot welding (RFSSW) technique on the mechanical properties and microstructure of aluminum AA5052 and AA6061-T3. Specimens were first prepared from AA5052 sheet of thickness 2 mm and AA6061-T3 of 1.6 mm, for chemical analysis and mechanical tests. Workpieces were then stir spot welded by RFSSW at four rotational speeds (2000, 2500, 3000 and 4000 rpm) using two tool pin diameters (5 and 7 mm) to carry out the tensile shear tests. Microhardness testing was conducted at the best conditions along the cross-section of the welded specimens, as well as microstructure examination. The results of the tensile shear tests manifested that, for AA5052 and AA6061-T3 at the tool rotational speeds 2000 rpm and 3000 rpm, respectively, using a tool pin of 7 mm the ultimate tensile shear force was slightly higher than at other speeds in both diameters of tool pin (5 and 7 mm). However, the microhardness results displayed a W-shape at the best conditions. Finally, the microstructure inspection revealed the morphology of the major zones of the weld joint.

Experimental and Numerical Investigations of Thin-Walled Stringer-Stiffened Panels Welded with RFSSW Technology under Uniaxial Compression.

Many aircraft structures are thin walled and stringer-stiffened, and therefore, prone to a loss of stability. This paper deals with accurate and validated stability analysis of the model of aircraft skin under compressive loading. Both experimental and numerical analyzes are conducted. Two different methods of joining panel elements are considered. In the first case, the panel is fabricated using rivets. In the second variant, the refill friction stir spot welding technique is used. Both types of panels are loaded in axial compression in a uniaxial tensile testing machine. The geometrically and physically nonlinear finite element analyzes of the panels were carried out in ABAQUS/Standard. The Digital Image Correlation measurement system ARAMIS has been utilized to monitor the buckling behavior and failure mode in the skin-stringer interface of the stiffened panels. The results of experiments and the digital image correlation system are presented and compared to the numerical simulations.

Friction stir spot welding of SPCC low carbon steel plates at extremely low welding temperature

Friction stir spot welding (FSSW) was applied to 2.0 mm thick steel plate cold-rolled commercial (SPCC) low carbon steel plates at a very low rotation speed that ranged from 5 to 50 rpm, which was much lower than that generally used for the conventional FSSW technique. Due to the very low heat input, the welding processes could therefore be completed at a peak welding temperature below 160 °C. As a result, a significantly refined microstructure with an average grain size of about 0.41 μm was formed in the stir zone of the joints and the J1{0–11}<−211> and J2{1–10}<−1–12> shear textures were the dominant components, which are different from the D1{11–2}<111> and D2{−1–12}<111> shear textures formed in the conventional FSSW joints. In addition, no heat affected zone could be detected along the cross-sectional plane of the joints. Although a few void-like non-bonded areas were still observed along the interface between the upper and lower steel plates, the shear tensile loads of the joints increased to about 10.0 kN when welded at a condition of 8 t, 20 rpm and 30 s, and the joints fractured through the plug failure mode.

Flat friction stir spot welding of three 6061-T6 aluminum sheets

Three 6061-T6 aluminum sheets with a thickness of 1 mm for each were subjected to the flat friction stir spot welding technique, which contains two steps of welding process. In step 1, a specially designed back plate with a pre-drilled dent was used in order to form a protuberance on the bottom side of the joint. In step 2, the keyhole and the protuberance were removed by using a probe-less rotating tool and a smooth back plate. The optimized welding condition for the three sheet spot welding was 700 kg/550 rpm/2 s in step 1 and 1000 kg/600 rpm/2 s in step 2. Two sheet/sheet interfaces were formed in the bowl-like stir zone. The stir zone showed a grain size varied from 4.2 to 8.6 μm, much smaller than the 17.6 μm of the base metal. Three different tensile test modes were used to evaluate the failure behavior of the joints. The interface between the top and middle sheet showed a longer bonding length of 11.5 mm and a higher fracture load of about 6438 N. While the interface between the middle and the bottom sheet showed a bonding length of 5.2 mm and a fracture load of about 4450 N. The step 2 joints showed plug-type failure mode during the shear tensile tests.

Improving the joint strength of the friction stir spot welding of carbon steel and copper using the design of experiments method

Purpose The purpose of this paper is to optimize the welding parameters: rotating speed and plunging depth of carbon steel and pure copper joints using friction stir spot welding (FSSW) with the aid of the design of experiments (DOE) method. Design/methodology/approach Carbon steel and pure copper sheets were welded using the FSSW technique with a cylindrical tool and without a probe. The welding parameters were: rotating speed: 1,120, 1,400 and 1,800 RPM and plunging depth: 0.2 and 0.4 mm. The welding process was carried out both with and without pre-heating. The welded specimens were analyzed using a shear tensile test. A microstructural investigation at the optimum conditions was carried out. The results were analyzed and optimized using the statistical software Minitab and following the DOE method. Findings Pre-heating the sample and increasing the rotating speed and plunging depth increased the tensile shear force of the joint. The plunging depth has the biggest effect on the joint efficiency compared with the rotating speed. The optimum shear force (4,560 N) was found at 1,800 RPM, 0.4 mm plunge depth and with pre-heating. The welding parameters were modified so that the samples were welded at 1,800 RPM and at plunging depths of 0.45–1 mm in 0.05 mm steps. The optimized shear force was 5,400 N. The fractured samples exhibited two types of failure mode: interfacial and nugget pull-out. Originality/value For the first time, pure copper and carbon steel sheets were welded using FSSW and a tool without a probe with ideal joint efficiency (95 percent).

Ultrafine grained structure and improved mechanical properties of low temperature friction stir spot welded 6061-T6 Al alloys

In this study, 1mm thick 6061-T6 aluminum alloy plates were subjected to friction stir spot welding (FSSW) at a very low rotation speed of 30, 40 and 50rpm, aiming to prevent the hardness reduction in the heat affected zone (HAZ) of this precipitate hardening Al joints. Two kinds of rotating tools, namely, one with a 1mm long probe and the other one with a flat shoulder without a probe, were used and the corresponding force applied to the rotating tools was ranged from 4 to 8tons. Under this special welding condition, the highest welding temperature was measured lower than 200°C. As a result, no hardness reduction of the HAZ region could be detected and an ultrafine grain structure with a high density of dislocations was formed in the stir zone. The average grain size obtained in the stir zone was less than 500nm for all the welds, which was much smaller than that in conventional FSSW processed 6061-T6 Al joints. In addition, no hook-like bonding ligaments were formed in the joints due to the very different material flows and the shear tensile tests showed that the spot welds prepared by the low speed FSSW can reach a maximum shear load of about 5400N, much higher than those prepared by the conventional FSSW technique.

Development of processing windows for friction stir spot welding of aluminium Al5052 /copper C27200 dissimilar materials

Friction stir spot welding technique was used to join dissimilar combinations of aluminium alloy (Al5052) with copper alloy (C27200) and friction stir spot welding windows such as tool rotational speed–dwell time and tool rotational speed–plunge depth diagrams for effective joining of these materials were developed. Using a central composite design model, empirical relations were developed to predict the changes in tensile shear failure load values and interface hardness of the joints with three process parameters such as tool rotational speed, plunge depth and dwell time. The adequacy of the developed model was verified using ANOVA analysis at 95% confidence level. Response surface methodology was used to optimize the developed model to maximize tensile strength and minimize interface hardness. A high tensile shear failure load value of 3850 N and low interface hardness value of HV 81 was observed for joints made under optimum conditions, and validation experiments confirmed the high predictability of the developed model with error less than 2%. The operating windows developed shall act as reference maps for future design engineers in choosing appropriate friction stir spot welding process parameter values to obtain good joints.

Effect of Dwell Time on Joint Interface Microstructure and Strength of Dissimilar Friction Stir Spot-Welded Al-5083 and St-12 Alloy Sheets

Joining of Al-5083 alloy sheet to St-12 steel sheet was performed using a new friction stir spot welding (FSSW) technique in which the tool pin tip did not enter lower steel sheet. Effect of dwell time on the microstructure and mechanical properties of the joints was studied by various methods including microhardness measurements, shear test, stereo and light microscopy as well as scanning and transmission electron microscopy (SEM and TEM). Results indicated that compared to the conventional FSSW process, stronger joints can be achieved by this FSSW technique. Cross-sectional observation of the failed specimens indicated the occurrence of final fracture from the circumference of the tool pin where the Al sheet thickness was decreased as a result of the tool pin penetration. However, microhardness measurements introduced these fracture locations as the hardest regions of the Al part of welds. In addition to the Al3Fe and Al5Fe2 intermetallic compounds reported in the literature to form at the interface of dissimilar Al/steel joints, a third layer of AlFe intermetallic compound was also identified adjacent to the steel side of welds. Enhancement of the dwell time from 5 to 15 seconds increased the intermetallic layer thickness from ~1.7 to ~3 µm and resulted in the formation of harder stirred zone. This consequently increased the strength of the weld.

Material behaviour characterization of Friction Stir Spot Welding of Copper

Friction stir spot welding (FSSW) is considered as a replacement technology of conventional resistance spot welding for manufacturing lighter vehicles in the automotive industry. FSSW technique was applied to join pure copper for industrial uses. The welding was conducted on an Intelligent Stir Welding for Industry and Research (I-STIR) Process Development System (PDS). Rotational speeds of 1200, 1600 and 2000 rpm were employed. The spot welds were characterised through the evolving microstructure, microhardness, tensile and the fracture surfaces. The microhardness measurements were conducted using the Vickers microhardness indenter and the tensile shear test was used to determine the mechanical properties of the welds. Optical microscope and scanning electron microscopy technique (SEM) were used for the microstructure analysis while the Energy Dispersive X-ray spectroscopy (EDS) was used to analyse the debris observed in the specimens after welding. It was found that the microhardness profiles of the processed samples revealed a decrease in the hardness value at the joint interface of the weld, this results in the lower strength of the welds, this is attributed to the heat and the stirring process generated during the processing due to a large stir zone. The process was evaluated in order to make it an alternative welding technique and to produce a material with high strength for industrial application. Microstructure evolution and the mechanical characterization techniques were employed to evaluate the properties of the welded materials. It was deduced that the rotational speeds employed influenced the evolving properties of the welded specimens.

Evolving properties of friction stir spot welds between AA1060 and commercially pure copper C11000

Friction stir spot welding technique was employed to join pure copper (C11000) and pure aluminium (AA1060) sheets. The evolving properties of the welds produced were characterized. The spot welds were produced by varying the rotational speed, shoulder plunge depth using different tool geometries. The presence of a copper ring of different lengths was observed on both sides of the welds indicating that Cu extruded upward into the Al sheet which contributed to obtaining strong welds. The microstructure showed the presence of copper particles in the aluminium matrix which led to the presence of various intermetallics observed by the energy dispersive spectroscopy and X-ray diffraction. The maximum tensile failure load increases with an increase in the shoulder plunge depth, except for the weld produced at 800 r/min using a conical pin and a concave shoulder. A nugget pull-out failure mode occurred in all the friction stir spot welds under the lap-shear loading conditions. High peaks of Vickers microhardness values were obtained in the vicinity of the keyhole of most of the samples which correlated to the presence of intermetallics in the stir zone of the welds.

Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile–shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile–shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.

Microstructure and mechanical properties of mild steel joints prepared by a flat friction stir spot welding technique

With the successful application of the flat spot friction stir welding technology to aluminum alloys, this technique was expanded to the spot lap welding of 1mm thick mild steel in this study. It reveals that sound joints can be successfully obtained with smooth surfaces and without any internal welding defects. Two welding strategies based on the welding parameter can be used to obtain the welds that fracture through plug failure mode at high shear tensile strength. One way is to weld the sheet at low heat input in the first step and the second step is used to generate large stir zone and flatten the sample surface. However, the microstructure in the stir zone is not homogeneous and a coarse columnar grain structure forms at the bottom of the stir zone. Another way is to make the stir zone penetrate into the lower sheet during the first step and the second step is only aimed to flatten the sample surface. In this case, the total heat input can be reduced and the microstructure of the stir zone can be remarkably refined. The sound joints fractured along the circumstance of the stir zone and reached about 6600N during the shear tensile tests.

마찰교반점접합한 5454-O 알루미늄합금 판재의 접합부 거시조직 및 기계적 특성에 미치는 접합인자의 영향

Friction stir spot welding between 5454 aluminum alloy sheets with the different thicknesses of 1.4 and 1.0 mm was performed. In the welding process, the tool for welding was rotated ranging from 500 to 2500, and plunged to the depth of 1.8 mm under a constant tool plunge speed of 100 mm/min. And then, the rotating tool was maintained at the plunge depth during the dwell time ranging from 0 to 7 sec. The pull-out speed of the rotating tool was 100 mm/min. The increase of tool rotation speed resulted in the change of the macrostructure of friction-stir-spot-welded zone, especially the geometry of welding interface. The results of the tensile shear test showed that the total displacement and toughness of the welds were increased with the increase of the tool rotation speed, although the maximum tensile shear load was decreased. However, the change in the dwell time at the plunge depth of the tool did not produce the remarkable variation in the macrostructure and mechanical properties of the welds. In all cases, the average hardness in friction-stir-spot-welded zone was higher than that of the base metal zone. By the friction stir spot welding technique, the welds with the excellent mechanical properties than the mechanically-clinched joints could be obtained.