Friction Spot Welding Research Articles

Joining of Polymer to Aluminum Alloy AA1050 By Friction Spot Welding

The friction spot welding process is used to join the hybrid joint of aluminium to polymer. AA 1050 Aluminum alloy and polyethylene polymer (type of plastic) were used for joining. Aluminium surface treatment was done to increase the wettability of it. The surface treatment was done by electrochemical treatment. Two parameters of the joining process were used: (1, 1.5 and 2) min. (920, 1340 and 1500) rpm for time and rotational speed, respectively. Many tests for the joint are done: shear test and Scanning electron microscopy (SEM). Using the Minitab program, the effect of the parameters on the joint was analysed. The maximum value of the shear force was (1587 N) at 1.5 min. time and 1340 rpm rotational speed. The minimum shear force was (589 N) at 1 min. time and 920 rpm rotational speed. The joints which were tested failed by an interfacial shear with a ductile fracture of the polymer side. The process of joining mechanism occurred through a mechanical interlocking between the molten polymer and the surface of the AA 1050 aluminium specimen, cohesive and adhesive. The average thickness for the joint of the tested specimens was 4µm.

Predicting the weld zones size in FSSW of 304L stainless steel plates by mathematical model based on RSM

The 300 series austenitic stainless steels are widely used in industries due to their special properties. High heat in fusion welding reduces the properties of these steels and causes many problems. Therefore, stir friction spot welding, which is a type of solid state welding, is useful and widely used in high-tech industries. In this paper, a 3D dynamic explicit finite element model is developed to simulate the friction stir spot welding of 304L stainless steel plates. Using this model, the temperature distribution and the size of weld zones (thickness of weld zones) are obtained. Then, by experimental study, the results of the temperature and the size of weld zones were obtained to be a criterion for comparing and validating the numerical results. Microstructure and hardness of these zones are determined experimentally. Finally, a mathematical model based on the response surface methodology is proposed to predict the size of weld zones. Good agreement between the numerical results that are produced by the finite element simulation, the proposed model and the experimental data is observed. The results show the maximum temperature level appears in the stir zone and it reduces by moving from the weld center. Also, by increasing the rotational speed, plunging depth and dwell time of the tool, the size of both the stir zone and the heat affected zone increase to a peak value and then the size of the latter zone decreases.

Friction spot welding multilayer thin Al alloy: Welding mode optimization, microstructure and mechanical properties

In this work, multilayer thin 2024 Al alloy sheets are joined by friction spot welding (FSpW). The effects of welding mode on the microstructure and mechanical properties of the joints are mainly studied. Results show that numerous tiny cracks are observed in the bonding ligament in the joint by single side FSpW, while these cracks can be eliminated by double side FSpW. In the double side FSpW joint, the grains are coarse in the joint center. The grain size increases from the top to the bottom of the joint by single side FSpW. The double side FSpW joints have obviously higher failure loads that the single side FSpW joints. The highest failure strength of 395.6 MPa is obtained at 1200 rpm by double side FSpW.

Effects of Rotational Speed on the Microstructure and Mechanical Properties of 2198-T8 Al-Li Alloy Processed by Friction Spot Welding

The friction spot welding (FSpW) method was used to weld 2198-T8 Al-Li alloy at rotational speeds of 500 rpm, 1000 rpm, and 1800 rpm. It was shown that the grains in the FSpW joints were transformed from "pancake" grains to fine equiaxed grains by the heat input of welding, and the reinforcing phases of S' and θ were all redissolved into the Al matrix. This leads to a decrease in the tensile strength of the FsPW joint compared to the base material and a change in the fracture mechanism from mixed ductile-brittle fracture to ductile fracture. Finally, the tensile properties of the welded joint depend on the size and morphology of the grains and their dislocation density. At the rotational speed setting of 1000 rpm in this paper, the mechanical properties of welded joints consisting of fine and uniformly distributed equiaxed grains are best. Therefore, a reasonable set of the rotational speed of FSpW can improve the mechanical properties of the welded joints of 2198-T8 Al-Li alloy.

Ultrasonic inspection technology of welded joints obtained by spot friction welding

Friction stir welding has found wide application in the aircraft and rocket industries, primarily due to the possibility of obtaining welded joints with a strength close to that of the base material. One of the most promising methods of such welding is friction stir spot welding, which can serve as an alternative to electric contact spot welding and riveting of joints. To introduce friction stir spot welding into the production of critical products, it is necessary to consider issues related to non-destructive quality control of welded joints obtained by this welding method. The purpose of this work is to substantiate the applicability of the ultrasonic echo method for quality control of welded joints obtained by friction stir spot welding. The relevance of the work is confirmed by the fact that today there is no sufficiently complete information on the results of experimental studies aimed at analyzing the characteristics of welded joints obtained by friction stir spot welding. The authors of the article proposed to use the ultrasonic echo method of control. The control was carried out using an ultrasonic flaw detector with a separate-combined piezoelectric transducer on samples of welds made using friction stir spot welding. Flaws such as lack of penetration and root sticking were found in three samples as a result of ultrasonic testing, which was confirmed by metallographic studies. Samples in which no defects were found were subjected to mechanical tests, as a result of which it was found that the strength of the obtained welded joints is comparable to the strength of the base metal of the samples. Metallographic studies were carried out on samples after the absence of defects in welded joints was confirmed through mechanical tests. Thus, the relationship between the results of ultrasonic testing, metallographic studies, and mechanical tests is shown, which makes it possible to justify the applicability of the ultrasonic echo method for quality control of welded joints obtained by friction stir spot welding.

Microstructural and Mechanical Properties of AZ31B to AA6061 Dissimilar Joints Fabricated by Refill Friction Stir Spot Welding

Dissimilar friction stir spot welds (FSSW) between the magnesium and aluminum alloys are joined, using a novel approach called refill friction stir spot welding. The present work aims to evaluate the macrostructural and mechanical properties of refill friction stir spot welded AZ31B and AA 6061-T6 alloys in two combinations, i.e., identical Mg-to-Mg and dissimilar Mg-to-Al joints, and the results are compared with the results obtained in conventional friction stir spot welding. The hardness profiles of the similar welds had the appearance of a W-shape, and the Thermo mechanically affected zone and heat-affected zone of both methods had lower hardness values than the rest of the weld. Along with the interface between the aluminum and magnesium sheets, a thin intermetallic compound layer of Al12Mg17 has been identified, which has led to an increase in hardness. The static shear strength of both similar and dissimilar refill spot friction welds was much greater than that of traditional spot friction welds. In both similar and dissimilar spot friction welds, two distinct failure scenarios are discovered.

Clinical and radiological outcomes of Chinese customized three-dimensionally printed total temporomandibular joint prostheses: A prospective case series study

Temporomandibular joint (TMJ) diseases are highly prevalent in China. However, no commercialized custom-made prostheses are available now. This study introduces a three-dimensionally (3D) printed customized total TMJ prosthesis manufactured by a standardized workflow. Consecutive patients with end-stage TMJ diseases were recruited from Jan 2018 to Sep 2018. The computed tomography (CT) data for patients were obtained and transformed into the Mimics 18.0 software preoperatively for designing of prostheses and digital templates. 3D printing, friction spot welding and computer-assisted manufacture (CAM) were used to fabricate different components of the prosthesis. The clinical and radiographic evaluations were performed postoperatively. A series of 9 patients were included. All the prostheses were placed smoothly and fixed stably during surgical procedure. Without severe postoperative complications, all patients exhibited significant improvements in maximum mouth opening, pain, diet, and mandibular function, with good facial symmetry. For the whole prosthesis, the average mean deviation was 0.432 mm (range: from 0.279 to 0.561 mm). This study suggests that Chinese customized 3D-printed total TMJ prostheses produces excellent short-term clinical outcomes, with high accuracy in implantation.

Achieving a strong polypropylene/aluminum alloy friction spot joint via a surface laser processing pretreatment

Strong metal/non-polar plastic dissimilar joints are highly demanded for the lightweight design in many fields, which, however, are rather challenging to achieve directly via welding. In this study, we designed a laser processing pretreatment on the Al alloy to create a deep porous Al surface structure, which was successfully joined to the polypropylene (PP) via friction spot welding. A maximum joint strength of 29 MPa was achieved, the same as that of the base PP (i.e. the joint efficiency reached 100%), much larger than ever reported. The joining mechanism of the Al alloy and the PP was mainly attributed to the large mechanical interlocking effect between the laser processed Al porous structure and the re-solidified PP and the formation of chemical bond at the interface. The deep porous Al surface structure modified by laser processing largely changed the Al‒PP reaction feature. The evidence of the COAl chemical bond was first time found at the non-polar plastic/Al joint interface, which was the reaction result between the oxide on the Al alloy surface and thermal oxidization products of the PP during welding. This study provides a new way for enhancing metal-plastic joints via surface laser treatment techniques.

Refill Friction Stir Spot Welding of Similar and Dissimilar Alloys: A Review

Refill friction stir spot welding, also known as friction spot welding (FSpW), is a solid-state welding process suitable for spot joining of lightweight materials. Through the efforts of improving joint quality for similar and dissimilar materials, for example, aluminum and magnesium, this joining technology is well developed. The joining mechanism and process characteristics of FSpW have been widely studied. However, the application of FSpW in industry has not been entirely successful. In this review article, the research of similar and dissimilar material joints, such as, Al/Cu, Al/Ti, Al/Mg and Al/Steel, is summarized. The microstructural features and mechanical properties of the joints, welding tool and the application development are discussed in detail.

Modeling heat input when friction stir welding

An important element of friction stir welding technology is the determination of the temperature of the material in the mixing zone, which can be determined by calculating the amount of heat introduced into the welding zone. To determine this value, experimental studies were carried out on a stand in which the material to be welded (aluminum alloy AMg5) is modeled as an experimental tube with a diameter of 20 mm, and the tool (from tool steel P6M5) is modeled as a working plate. On the stand, studies of the dependence of the frictional moment and heat-liberation value were performed. According to the obtained experimental data, the heat-liberation dissipation and heat power on the working tool are calculated, the dependences of these values on the radius of the working tool are obtained.To increase the amount of heat input in the center of the contact area, a tool with a drive with two concentrically located (one inside the other) shafts is proposed, while the inner shaft rotates at a higher speed than the outer one. According to the obtained experimental data, the dependences of heat release for each shaft and the total heat release for a tool with two shafts at an external shaft rotation speed ω = 63 s-1 and different rotation speeds of the internal shaft are calculated. In total, for the external and internal shafts, the total heat release value is about 2 times higher than the total heat release value using a single shaft.The purpose of this work is to find the values of heat release in friction stir spot welding, as well as the development of friction spot welding tools with higher heat release.

Joining Dissimilar Mg/Al Alloys by Solid-State Friction Spot Welding

To reduce intermetallic compounds (IMCs), dissimilar Mg/Al alloys were joined by solid-state friction spot welding. No incomplete refilling was observed when Al sheet served as the upper sheet. Almost no IMCs formed at the sleeve-affected zone even though the sleeve plunged during welding. A 530-µm-thick Al12Mg17 layer formed at the center of the Al/Mg joint due to a large amount of liquid phase formed during welding. Only a 5-µm-thick Al3Mg2 layer formed in the Mg/Al joint because the oxide film on the Al sheet was difficult to break. The Al/Mg joint exhibited much higher lap shear failure load even though it had a thicker IMC layer. The joint formation mechanism was studied.

Investigation of geometrical features on mechanical properties of AA2198 refill friction stir spot welds

Geometrical features such as stir zone area, hook and bonding ligament of refill friction spot welds produced from AA2198 3.2 mm-thick sheets were analyzed along with their lap shear strength (LSS) and failure mode. Macro and micrographs of weld cross-sections were analyzed using optical microscopy for the understanding of microstructure development and measurement of stir zone area (SZA) and hook height (H). The comparison between SZA and LSS variation indicates a good correlation between these two variables while the hook effect does not present an obvious correlation with the LSS along the different welding conditions. Furthermore, analysis of variance of SZA considering rotational speed (RS), welding time (WT) and plunge depth (PD) shows that the variance of PD is responsible for more than 85% of the variation in SZA. A close relationship between defects and fracture type was also established since the hook and bonding ligament are preferential regions for nucleation and growth of circumferential and annular crack, respectively. All the welds presented the through-the-weld type of fracture, in which the nugget tears apart under loads. Circumferential crack growth was observed to play an important role in weld resistance as it prevents the annular crack growth, which is responsible for the final fracture. Lastly, the association between circumferential crack growth and PD shows a major influence on LSS since the path created by the sleeve plunge is a region of preferential crack growth.

A study of the parameters influencing mechanical properties and the fatigue performance of refill friction stir spot welded AlMgSc alloy

Friction spot welds of 1.6-mm-thick AlMgSc alloy were investigated in this work. A design of experiment method was used to evaluate the effect of process parameters on the shear static strength. The optimized condition of parameters was employed in the assessment of the fatigue behavior. The typical hook feature was minimized by restricting the tool penetration into only the upper sheet. As a consequence, shear strength was sensitive to the extension of the welded region rather than the hook morphology. The fatigue performance was affected by the multiple crack initiation sites that resulted from a complex stress state during the axial loading. Striations were observed in practically the entire crack propagation region, suggesting that unstable fatigue crack growth did not take place in this specific weld configuration.

Effect of friction spot welding parameters on the joint formation and mechanical properties of Al to Cu

Friction spot welding is an appealing technique for joining dissimilar materials, such as aluminum and copper that have significant differences in physical and mechanical properties. To optimize the welding process, a full-factorial design was employed. It is found that in addition to the plunge depth, the interaction between the rotational speed and the plunge depth significantly influences the lap-shear strength of the Al/Cu dissimilar joints. Further investigations on macro- and microstructures show that increasing the plunge depth could deform the Cu sheet into a concave shape to form a mechanical interlocking, and thus increase the joint lap-shear strength; increasing the tool rotational speed, however, may compromise this effect because of the formed tunnel defects on the interface due to high thermal exposure.

Numerical study on a thermal process in friction spot welding of Al-Zn-Mg-Cu alloy

A three-dimensional coupled thermo-mechanical model under consideration of local melting was developed to study the temperature distribution and thermal cycles during friction spot welding of Al-Zn-Mg-Cu alloy. The results indicate that the high-temperature region during welding was located in the sleeve cavity and the temperature gradient was higher in the thickness direction in the stir zone (SZ). At relatively high plunging depth and rotation speed, the peak temperature in the SZ was higher than the solidus temperature of Al-Zn-Mg-Cu alloy (532 °C). The peak temperature in thermal mechanically affected zone (TMAZ) was higher than the solution temperature (300 °C) but lower than the solidus temperature. The peak temperature in the heat-affected zone (HAZ) was higher than the aging temperature (170 °C). With the increase of the sleeve plunging depth, the peak temperatures in all the zones constantly increased. With the increase of the tool rotation speed, the peak temperature in the SZ and TMAZ first increased and then decreased, while the peak temperature in the HAZ constantly increased.

Experimental Investigation on Friction Stir and Spot Welding of AA 6061 and Its Strength Measurements

An experimental investigation has been meted out on Hardness distribution, tensile properties and microstructure of weld, butt joints of 6061 metallic element alloy. Two completely different fastening methods are considered: Associate in nursing innovative solidstate fastening method referred to as friction stir fastening (FSW) process and Friction Stir spot fastening. The shaping pressure and mix of the plasticized material lead to the formation of a solid bond region in friction stir spot fastening (FSSW) Instead, in FSW joint, lower temperatures area unit concerned within the method because of severe plastic deformation induced by the tool motion and lower decay of mechanical properties. Within the hunk zone, a small recovery of hardness is ascertained because of recrystallization of terribly fine grain structure. Therefore, from industrial views, FSW method is incredibly competitive assist saves energy, has higher lastingness and prevents the joints from fusion connected defects. FSW is one of the important welding processes that can be adopted for welding of Aluminum alloys with excellent mechanical properties.

Friction spot welding of carbon fiber-reinforced polyetherimide laminate

Here, carbon fiber-reinforced polyetherimide (PEI) laminate was joined via friction spot welding (FSpW). The feasibility and fracture mechanism of the FSpW joints were investigated. The sound joint with smooth surface and without hook defect was achieved. The strong bonding formed at the sleeve stirring zone and thermo-mechanically affected zone, resulting from the macromolecular interdiffusion and interlocking of the smashed carbon fiber at the bonding interface by thermo-mechanical behavior. Increasing rotational velocity enhanced the mixing degree of the carbon fiber at the interface and strengthened the bonding interface, which improved tensile shear properties. The maximum tensile shear load of the FSpW joint with a joining area of 66.4 mm2 reached 1600 N, which was comparable to the strength of state-of-the-art welding. The fracture surface morphologies revealed a typical ductile fracture containing the deformation of polymer and the pull-out of the carbon fiber. The FSpW has feasible and potential to join carbon fiber-reinforced thermoplastic composites laminate.

Experimental Investigation on Friction Stir and Spot Welding of AA 6061 and it\'s Strength Measurments

Experimental Investigation on Friction Stir and Spot Welding of AA 6061 and it\'s Strength Measurments

Local melting mechanism and its effects on mechanical properties of friction spot welded joint for Al-Zn-Mg-Cu alloy

Local melting and the eutectic film and liquation crack formation mechanisms during friction spot welding (FSpW) of Al-Zn-Mg-Cu alloy were studied by both experiment and finite element simulation. Their effects on mechanical properties of the joint were examined. When the welding heat input was high, the peak temperature in the stir zone was higher than the incipient melting temperature of the Al-Zn-Mg-Cu alloy. This resulted in local melting along the grain boundaries in this zone. In the retreating stage of the welding process, the formed liquid phase was driven by the flowing plastic material and redistributed as a “U-shaped” line in the stir zone. In the following cooling stage, this liquid phase transformed into eutectic films and liquation cracks. As a result, a new characteristic of “U” line that consisted of eutectic films and liquation cracks is formed in the FSpW join. This “U” line was located in the high stress region when the FSpW joint was loaded, thus it was adverse to the mechanical properties of the FSpW joint. During tensile shear tests, the “U” line became a preferred crack propagation path, resulting in the occurrence of brittle fracture.

Metallographic evaluation of the weldability of high strength aluminium alloys using friction spot welding

Friction spot welding is a recent solid-state welding technique well suited for spot-joining lightweight materials in overlap condition. Aerospace and transport industries show great interest in this technique to join high-strength aluminium alloys, but published research is still limited. In this project, the link between process parameters and weld quality is investigated for EN AW-7075-T6 material. Techniques used are metallographic qualification, measurement of hardness reduction and lap shear strength. This paper focusses on the metallographic investigation of the weld region and its imperfections. Increasing joining time and heat input creates an easier material flow resulting in fewer imperfections. Limited plunge depths lead to typical interface imperfections. Variation in the rotational speed shows distinctive stir zone shapes as a consequence of severe stirring and frictional heat.