Tool Plunge Depth Research Articles

Study on the Process of Preparing Aluminum Foam Sandwich Panel Precursor by Friction Stir Welding

In recent years, high-performance lightweight and multifunctional aluminum foam sandwiches (AFSs) can be successfully applied to spacecraft, automobiles, and high-speed trains. Friction stir welding (FSW) has been proposed as a new method for the preparation of AFS precursors in order to improve the cost-effectiveness and productivity of the preparation of AFS. In this study, the AFS precursors were prepared using the FSW process. The distribution of foaming agents in the AFS precursors and the structure and morphology of AFS were observed using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS). The effects of the temperature and material flow on the distribution of the foaming agent during the FSW process were analyzed through experimental study and numerical simulation using ANSYS Fluent 19.0 software. The results show that the uniform distribution of the foaming agent in the matrix and excellent densification of AFS precursor can be prepared when the rotation speed is 1500 r/min, the travel speed is 25 mm/min, the tool plunge depth is 0.2 mm, and the tool moves along the retreating side (RS). In addition, the experimental and numerical simulations show that increasing the welding temperature improves the uniformity of foaming agent distribution and the area of AFS precursor prepared by single welding, shortening the thread length inhibits the foaming agent from reaching the upper sandwich plate and moving along the RS leads to a more uniform distribution of the foaming agent. Finally, the AFS with porosity of 74.55%, roundness of 0.97, and average pore diameter of 1.192 mm is prepared.

Experimental investigation and optimization of nano Al2O3 mixed FSWed joint between AA2024-T351 and AA7075-T651 by response surface approach

Additive mixed friction stir welding can be an innovative and novel method for enhancing the friction stir welding process. Thus, this research aimed to investigate nano Al2O3 effects on the mechanical and microstructure of FSWed joints using Al alloys AA2024-T351/AA7075-T651. The experiments were performed based on response surface approach based CCD twenty run with varying three factors: tool rotational speed (A: 800–1,200 rpm), welding speed (B: 20–60 mm/min), tool plunge depth (C: 0.2–0.4 mm) and fixed volume percentages of Al2O3 nano-particles (8%). Mechanical performances such as tensile, yield, and hardness tests have been performed and microstructural properties have been analyzed through SEM and microscopy. The statistical analysis shows that the tensile strength can be significantly affected by rotational speed (A), welding speed (B), tool plunge depth (C), interaction (AB, BC, AC), and quadratic term A2, B2 in the FSW process; yield strength was influenced considerably by main, interaction, and quadratic terms; main factors and quadratic terms A2, B2 and C2 significantly influenced hardness values. The fracture test revealed that the joints with Al2O3-reinforced AA2024-T351/AA7075-T651 alloys were more ductile and less brittle. The optimal conditions for FSW, tool rotational at 1,146 rpm, weld speed at 60 mm/min, and 0.4 mm plunge depth were responsible for higher tensile strength of 169 MPa, yield strength of 145 MPa, and micro-hardness values of 89 HRB due to the uniform nano-particle dispersions and better material mixing.

Non-destructive evaluation of FSW tool plunge depth in thin metallic sheet weld using low frequency ultrasonic Lamb waves signal

Thin aluminium alloy sheets find widespread application in industries such as automotive, marine, railway, and aerospace due to their high load capacity-to-weight ratio. Welding has emerged as an effective joining method, surpassing mechanical fasteners and semi-joining processes. However, fusion welding techniques are susceptible to hot cracking, leading to solidification and liquation cracking. When it comes to lap welded joints in thin metallic sheets, friction stir welding (FSW) has demonstrated exceptional efficiency. To assess weld morphology, non-destructive testing (NDT) methods are employed, with the ultrasonic method proving capable of measuring weld penetration depth in thick metallic plates using bulk and surface waves. Nonetheless, the role of tool plunge depth (TPD) in FSW, analogous to the weld penetration depth in fusion welding, remains unexplored through non-destructive means, despite its critical impact on the load carrying capacity of thin structures. Thisstudy aimsto predict the optimal tool plunge depth for achieving high-quality welding in thin structures by utilizing a guided Lamb wave-based non-destructive method. At a low frequency of 80 kHz, the transmission percentage of the anti-symmetric mode (A0) was calculated for FSW specimens with different tool plunge depths. The findings revealed that the transmission percentage was higher for welds with the optimum tool plunge depth compared to those with low and high tool plunge depths. This distinctive behavior of the specimens with the optimal TPD towards Lamb wave signals proved useful in predicting the FSW tool plunge depths.

Influence of tool plunge depth and multiple passes on the microstructure, texture evolution and hardness of age-hardenable aluminium 7075 alloy

In this study, the surface properties of AA7075 were modified through the solid-state friction stir processing technique using a hexagonal-shaped H13 pin. Single pass friction stir processing was conducted at two different shoulder plunge depths at constant tool rotation and linear speeds with the resulting cross-sections being examined using optical macroscopy. Six friction stir processing passes were then carried out intermittently at optimal shoulder plunge depth and the corresponding microstructural evolution along the nugget was investigated using advanced microstructural characterization techniques such as electron backscatter diffraction and high-resolution transmission electron microscopy. Bulk texture examination was conducted using the neutron diffraction method, while hardness measurements were taken using Vicker's hardness testing machine. Single pass friction stir processing conducted at a shoulder plunge depth of 0.25 mm produced defect-free material consolidation with a refined grain structure along the nugget. Minimum grain size averaging 3.78 μm was observed at the top, while slightly increased grain sizes were noticed at the middle and bottom regions of the nugget. After 6 friction stir processing passes, grain size was reduced significantly averaging 1.84 μm at the top, while size at the pin-driven zone exhibited an increasing trend due to heat input and strain rate variations. Both, single-pass and 6 pass specimens exhibited a weaker texture along the nugget due to randomness in grain orientation and the effect of particle-stimulated nucleation mechanism. In the single-pass specimen, hardness decreased along the nugget, with a maximum of 85.2 HV at the top, while 6-pass specimen exhibited an improved hardness of 133.5 HV due to the strengthening caused by grain refinement, precipitates and dislocations.

The effect of RFSSW parameters on load capacity of EN AW-6082-T6 aluminum alloy and AlCu bimetallic joints

This paper presents research into the creation of refill friction stir spot welding (RFSSW) single-lap joints of 6082-T6 aluminum alloy and roll-bonded AlCu bimetallic sheet. The latter sheet comprises aluminum EN AW-1050A and electrolytic copper M1E in Z6 temper condition (after rolling) and with a 1:1 ratio of the Cu:Al layers. The welding parameters involved a variable plunge depth and welding time. The mechanical properties of the joints were determined in tensile/shear tests. The highest average value of the load capacity of the joint was observed in joints made with a tool plunge depth dt = 2.6 mm and total welding time tw = 4 s. The load capacity for this variant was an average of 5986.75 N with standard deviation SD = 166.15 N. A plug-type fracture on the aluminum layer of the bimetallic sheet was observed in RFSSW joints produced with a plunge depth of 2.6 mm. Increasing the tool rotational speed and thus generating heat resulted in a plug-type fracture on the upper sheet (aluminum alloy). In the case of joints produced with a plunge depth of 2 mm equal to the thickness of the upper sheet, the type of fracture mode with both welding times was found to be nugget debonding.

Friction stir welding of AA5010 aluminum alloy to St-12 carbon steel using CoCrCuFeNi high entropy alloy interlayer

Dissimilar friction stir welding (FSW) of AA5010 aluminum alloy to St-12 carbon steel using an equiatomic CoCrCuFeNi high-entropy alloy (HEA) interlayer was investigated. Mechanical properties of the joints fabricated under different plunge depths of the FSW tool were examined and correlated to microstructural evolutions. The incorporation of the HEA interlayer successfully prohibited the formation of AlFe intermetallic compounds (IMCs). Also, the interlayer was metallurgically consistent with both base metals, although quite thin complex IMC layer was formed at the aluminum/HEA interface as a result of sluggish diffusion of constituent elements of HEA towards the aluminum. The application of suitable plunge depth in the steel part, i.e. 0.2 mm, resulted in the perturbation of the HEA/steel interface and then the formation of interfacial mechanical interlocks that were beneficial to the strength of the joints. However, excessive FSW tool plunge depth caused large voids to form near hooks, acting as stress concentration areas during shear-tensile test. An appropriate plunge depth of the tool achieved an ideal joint that exhibited fracture from the aluminum side rather than the joint interfaces. It also provided a strength value as high as 80 % of the nominal strength of aluminum base metal.

Optimising aluminium 2024/7075 friction stir welded joints

ABSTRACT The present novel work is the investigation of dissimilar AA2024/AA7075 aluminium alloy friction stir spot welded joint. The input welding process parameters were analysed to determine the most influencing process parameter on mechanical and morphological properties of the weld. The welding process and input parameters were optimised by Box–Behnken design and response surface methodology. Among the enhanced mechanical characteristics, tensile shear force was observed to be enhanced to maximum being influenced by the rotational speed of the friction stir tool. Optimised performance characteristics were obtained by using desirability approach, and the resulting optimal input parameters were: Tool plunge depth = 3.3 mm, rotational speed of tool = 2000 rpm and Tool dwell time = 40 s. The optimal tensile shear force and hardness obtained were 4.18 kN and 134 HV, respectively, which were validated by comparing the experimental and predicted output response. The elemental composition and morphology of materials were tcharacterised by X-ray diffraction – scanning electron microscope, while the mechanical properties were analysed by tensile and Vickers hardness testing.

Optimization of aluminum-to-steel friction stir lap welding for the fabrication of high-integrity structural components

Friction stir lap welding is a solid-state joining technique used to effectively fabricate high-quality lightweight and energy-efficient hybrid structures by overlapping thin parts of Al and other similar or dissimilar alloys. In this study, friction stir lap welding between 6061-T651 Al and JAC270 45/45 galvanized steel sheets was investigated, considering both single-pass and double-pass protocols to optimize the process and quality of the resulting welds. The single-pass welding was first studied by conducting experiments at constant tool rotation and traverse speeds (1200 RPM and 1 mm/s) and various tool plunge depths (0.05, 0.2, and 0.4 mm). The microstructures and Al-steel interfaces of the welds were characterized using microscopy and energy-dispersive X-ray spectroscopy, and the weld strength was evaluated by lap shear tensile testing. The defects and intermetallic compounds that form at the Al-steel interfaces were identified as the limiting factors for the weld strength. The intermediate tool plunge depth of 0.2 mm resulted in the highest weld strength due to the least amount of interfacial defects and intermetallic compounds amongst the studied single-pass welds. A double-pass welding method was then developed to optimize the strength of the Al-steel lap welds. The selection of the processing conditions for the double-pass welding was guided by the behavior and properties of the single-pass welds. The double-pass welding successfully eliminated the defects and intermetallic compounds from critical locations, creating a robust Al-steel interfacial bond and significantly improving the weld strength. The knowledge and findings in this study can be applied to optimize the design, material integration, and mechanical properties of lap welds for high-integrity structural components.

Impact Forming of AA5052-H32 Sheets With Friction Stir Spot Welds Using a Shock Tube and Failure Assessment

Abstract In this present study, both the experimental and numerical investigations are carried out to understand the formability of AA 5052-H32 sheets of 1.5 mm thickness with friction stir spot weld (FSSW). A shock tube experimental facility is utilized in which a rigid hemispherical striker is propelled at a high velocity and deforms the FSSW sheets at high strain rates. In this analysis, the effect of different tool rotational speed and plunge depth on the FS spot welding outputs and forming outputs are understood. Furthermore, DEFORM-3D finite element (FE) code is used to perform FE simulation of both the FS spot welding and forming of the welded sheets interactively. During the forming analysis, a new strategy is followed to identify the rate-dependent mechanical properties that are incorporated during FE simulation. The tensile data obtained from the unwelded section of the sheet deformed using the shock tube is fit to the modified Johnson–Cook (MJC) model. In the case of the FS spot-welded region, a hardness-based multiplying factor is identified and used to obtain stress–strain data by fitting it to MJC model. The predicted temperature evolution during the FSSW is validated with the experimental data and a good correlation has been observed. The predicted material flow phenomenon gives an insight into the joint formation during FSSW. Various forming outputs such as deformation profile, crack pattern, and effective strain distribution predicted by MJC model in combination with Freudenthal damage model are compared with the experimental data, and the results have a fair agreement.

Defects analysis in friction stir processing of magnesium based surface composites

Friction stir processing (FSP) is an environment friendly method that works in the same way as friction stir welding (FSW). FSP is a method of reforming the mechanical characteristics of materials by applying a rotating tool's stirring motion to the substance whose mechanical properties need to be improved. It is an energy efficient process by forming fine, equiaxed grains with no porosity, no interfacial reactions or radiations. As a result, it's widely regarded as a safe and effective method for producing surface composites of acceptable quality. It faces a number of significant hurdles, including faults of its own design, which make the process susceptible to modification in order to establish itself as a dependable manufacturing method. This research gives a comprehensive analysis of defects often identified in FSP. According to the findings of this study, the majority of the flaws are caused by inadequate production of heat, inappropriate mixing of material around the pin, and insufficient accumulation of material at the rear of pin. The quantity of heat generated and material stirred is determined by a number of FSP factors, which, if not chosen correctly, might result in defect formation.The findings presented in this paper are based on extensive research literature and experimentation. The suggestions are prescribed in the form of defect features like the possibility of their occurrence, the major causative parameters, and recommendations for reducing them. In this study, the effect of FSP factors, such as tool plunge depth, on the creation of defects such as tunnels (tunnelling defect) and other defects during the processing of magnesium based composites is investigated. The function of plunge depth was discovered to be the cause of the tunnelling defect. Optical microscopy (OM) and field emission scanning electron microscopy (FESEM) were used to characterize the FSPed plates.

Effect of dwelling time and plunge depth on the joint properties of the dissimilar friction stir spot welded aluminum and steel

Sound joints of a far apart property, pure aluminum and mild steel, dissimilar materials were obtained by friction stir spot welding (FSSW) solid state joining process. Sheets of 2 mm thickness were overlapped and fixed with a fixture device then welded. Welding parameters that produced the sound joint were identified. Joints microstructure and mechanical properties were investigated. A microstructural investigation has revealed a creation of mechanical interlocking and discontinuous formation of the intermetallic compounds found at the interface. The intermetallic compound (IMC) layer thickness ranged from 6 μm to 17 μm with the optimum condition specimen, 800 rpm and 5 Sec dwell time. Tensile–shear test showed that failure load has increased with increasing tool plunge depth and rotational speed. After the optimum value of rotational speed, the shear failure load decreased. The maximum shear failure load of 2.15 KN attained at 800 rpm and 2.4 mm plunge depth.

Influence of Friction Stir Welding Parameters on Joint Defects, Temperature and Hardness of AA6061-T6 and S27JR Mild Steel FSW Joint

The influence of welding parameters such as tool plunge depth, tool travel speed and tool tilt angle on welding temperature during friction stir welding of AA6061-T6 and S275JR mild steel was the focus of this research. Thermocouple placed in the aluminum alloy plate prior to welding was used to measure the temperature during the welding of joints under different set of parameter values. Joint appearance as well as defects occurring on the surface or within the joint was observed. Microhardness profiles were also taken by measuring microhardness values across the cross section of joints. Excessive flash, tunnel defects and insufficient welding were the type of weld defects observed on different joints with different parameters. Defects were attributed to the varied parameter values affecting the heat generation as well as the flow of the plasticized material. Highest temperature was recorded by the joint fabricated using the largest tool plunge depth, owing to the increased downwards pressure. Microhardness profiles were seen to be similar for all the welded joints. A “plateau” of low microhardness value was observed for all joints associated with the thermomechanically affected zone (TMAZ) and heat affected zone (HAZ). A wider plateau was observed for joints welded with higher tool plunge depth due to higher temperature.

Effect of tool plunge depth (TPD) on the microstructure and mechanical properties of FSW dissimilar joints reinforced with SiC nano particles

The effect of varying tool plunge depth (TPD) on the distribution of silicon carbide (SiC) nano particle reinforcement in fabricating the composite friction stir weld (FSW) dissimilar joints of aluminium alloy plates of 2024-T351 to 7075-T65 was investigated. Taper threaded cylindrical (TTC) tool is employed to produce the composites at the weld nugget zone (WNZ) of FSW dissimilar joints by varying the TPD range 5.80 mm to 6.20 mm, and keeping the tool rotation speed (TRS), 1000 rpm, tool traverse speed (TTS), 40 mm/min and tool tilt angle, 2°, as constants. The microstructure studies carried out using optical microscopy (OM) and scanning electron microscopy (SEM) indicates that the interaction of tool probe, tool shoulder with materials and SiC reinforcement plays a significant role on weld joint properties. The lower TPD results in insufficient heat generation causing SiC nano particle to stretch towards the retreating side (RS). Higher TPD leads to adhering of particle to tool shoulder and decreased flow of material to advancing side (AS) of the weld region. The optimum TPD of 6.10 mm results in uniform distribution of SiC in the WNZ with a higher micro-hardness of 150 Hv and ultimate tensile strength (UTS) of 389 MPa, yield strength (YS) of 213 MPa and percentage elongation (%EL) of 10.7.

Effects of FSW Tool Plunge Depth on Properties of an Al-Mg-Si Alloy T-Joint: Thermomechanical Modeling and Experimental Evaluation.

One of the main challenging issues in friction stir welding (FSW) of stiffened structures is maximizing skin and flange mixing. Among the various parameters in FSW that can affect the quality of mixing between skin and flange is tool plunge depth (TPD). In this research, the effects of TPD during FSW of an Al-Mg-Si alloy T-joint are investigated. The computational fluid dynamics (CFD) method can help understand TPD effects on FSW of the T-joint structure. For this reason, the CFD method is employed in the simulation of heat generation, heat distribution, material flow, and defect formation during welding processes at various TPD. CFD is a powerful method that can simulate phenomena during the mixing of flange and skin that are hard to assess experimentally. For the evaluation of FSW joints, macrostructure visualization is carried out. Simulation results showed that at higher TPD, more frictional heat is generated and causes the formation of a bigger stir zone. The temperature distribution is antisymmetric to the welding line, and the concentration of heat on the advancing side (AS) is more than the retreating side (RS). Simulation results from viscosity changes and material velocity study on the stir zone indicated that the possibility of the formation of a tunnel defect on the skin–flange interface at the RS is very high. Material flow and defect formation are very sensitive to TPD. Low TPD creates internal defects with incomplete mixing of skin and flange, and high TPD forms surface flash. Higher TPD increases frictional heat and axial force that diminish the mixing of skin and flange in this joint. The optimum TPD was selected due to the best materials flow and final mechanical properties of joints.

Effect of tool plunge depth on the microstructure and fracture behavior of refill friction stir spot welded AZ91 magnesium alloy joints

We used refill friction stir spot welding (RFSSW) to join 2-mm-thick AZ91D-H24 magnesium alloy sheets, and we investigated in detail the effect of tool plunge depth on the microstructure and fracture behavior of the joints. A sound joint surface can be obtained using plunge depths of 2.0 and 2.5 mm. Plunge depth was found to significantly affect the height of the hook, with greater plunge depths corresponding to more severe upward bending of the hook, which compromised the tensile-shear properties of the joints. The hardness reached a minimum at the thermo-mechanically affected zone due to the precipitation phases of this zone as it dissolved into the α-matrix during the welding process. The fracture modes of RFSSW joints can be divided into three types: shear fracture, plug fracture, and shear—plug fracture. Of these, the joint with a shear—plug fracture exhibited the best tensile-shear load of 6400 N.

Experimental investigations to find the effect of post weld heat treatment (PWHT) on the microstructure and mechanical properties of FSW dissimilar joints of AA2024-T351 and AA7075-T651

In this present study, a Friction stir weld (FSW) technique is applied to fabricate the FSW joints of aluminium alloy plates of 2024-T351 and 7075-T651 in butt-joint arrangement using a FSW tool of shape taper threaded cylindrical (TTC). The FSW joints are produced using constant FSW parameters of tool rotation speed (TRS) of 650 rpm, tool traverse speed (TTS) of 150 mm/min and tool plunge depth (TPD) of 6.20 mm. Tensile and microstructure specimens are removed from the weld joint in the direction perpendicular to the tool traverse and across the weld region. Initially, each of these specimens are heat treated to solution temperature (400, 420, 440, 460, 480, 500 °C) for 1 h and tested for tensile properties. The heat-treated microstructure samples are examined for the presence of abnormal grain growth (AGG) in the weld nugget zone (WNZ), thermally affected zone (TMAZ), heat affected zone (HAZ) of the weld region using stereo-zoom microscope and scanning electron microscope (SEM). Microstructure specimens subjected to solution heat treatment up to 480 °C are stable and reveals no AGG. However, for 500 °C the microstructures are not stable and the presence of AGG in the weld regions are observed. At 480 °C, the tested specimen shows homogeneity in hardness distribution across the weld regions. Thus, solution temperature of 480 °C is chosen as an optimizing solution temperature. Further, the tensile specimens are subjected to ageing temperature with constant temperature of 180 °C for various durations range 5, 8 and 12 h. Thus, these experimental investigations indicate that the specimen subjected to solution treatment at 480 °C followed by ageing temperature of 180 °C for 12 h show higher ultimate tensile strength (UTS) of 435 MPa and percentage increase of 6.8% compared to the specimens without heat treatment having UTS of 407 MPa.

Formability and Instability Evaluation of Friction Stir Processed AA6063-T6 Tubes During End Forming and Numerical Prediction

In the present work, formability of friction stir processed (FSPed) AA6063-T6 tubes during end forming has been evaluated by monitoring load evolution and instability. FSP has been done at different tool plunge depths to study its effect. End expansion, reduction and beading of tubes are performed. Energy absorption capacity of the FSPed tubes is also evaluated. Both experiments and finite element (FE) simulations of end forming are carried out. During FE simulations in ABAQUS v6.17, the processed zone properties including plastic strain ratio and actual thickness are incorporated, along with raw material properties. Out of all the plunge depths, FSP zone made at 2.95 mm shows larger flow strength, ductility, strain hardening exponent and lower dislocation density. However, at 2.95 mm plunge depth, the tube encountered larger thinning due to larger ductility. Moreover, FSP zone having lower flow strength show larger thickening. The results also reveal that the FSP tubes have potential to replace raw tubes as it needs lower forming load and perform equally in specific energy absorption during end reduction and beading. Numerical predictions and experimental data agree well in terms of load requirement during expansion and reduction, while in beading, significant difference is observed after bead initiation. Though FSP tubes have potential applications, instabilities during end forming may restrict their applications at certain situations, which can be improved by FSP parameter optimization.

Characterization and Optimization of Flat Friction Stir Spot Welding of Triple Sheet Dissimilar Aluminium Alloy Joints

The method of flat friction stir spot welding (FFSSW) was used to investigate the tensile behavior of three thin dissimilar aluminium alloys (Two sheets of AA6082-T6 and one sheet of AA6061-T6). Tool with probe and a probe less tool is used in this two-step process of joining. Experiments were conducted at various tool tilt angles (TTA), tool rotational speeds (TRS), dwell time (DT) and Tool plunge depths (TPD). The quality welds were produced at optimized process parameters (TTA 20, TRS 2125 rpm, DT 15 s and TPD 0.1 mm). Elimination of protuberance and reduction of keyhole in the joint is achieved for improving bonding length. Micrographs of joints were examined using optical microscopy and scanning electron microscopy (SEM). The complete bonding with finer grains at stir zone (SZ) improved the strength of FFSSW joint. Energy-dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis of specimen indicates the presence of Mg2Si precipitates in SZ. The fracture behavior of upper and lower interfaces was examined. The finer dimples are observed in fractograph, which confirm the ductile behaviour of fracture. The morphology at tool surfaces was also studied. The mechanical properties of three-sheet FFSSW joints were compared with other similar techniques of joining. Better understanding of mechanical properties and weld behavior of three sheets FFSSW is done with the help of fractography and SEM.

Effect of tool pin geometry on microstructure and mechanical properties of friction stir spot welds of 7075-T651 aluminium alloy

7075-T651 aluminium alloy sheets were overlapped and friction stir spot welded using two welding tools having different pin geometries (one with a conical pin and other with a triangular pin) and 800, 1200 and 1600 revolution per minute (rpm) tool rotation speeds at a constant tool plunge and removal speed of 7.3 mm/min, tool plunge depth of 3.8 mm and tool dwell time of 5 s. Microstructure, Vickers microhardness, tensile shear strength, fracture surface after tensile shear test and impact energy of the produced friction stir spot welds were examined. As a result, the welds made via triangular pin tool had considerably higher tensile shear loads than the welds made via conical pin tool since the weld bond widths (stir zones) of the welds made via triangular pin tool were larger. The strongest welds made at 1200 rpm for conical pin tool and triangular pin tool. The tensile shear loads of the welds increased significantly when tool rotation speed increased from 800 to 1200 rpm for both welding tools and then decreased slightly for triangular pin tool and dramatically for conical pin tool with further increasing tool rotation speed from 1200 to 1600 rpm. Maximum tensile shear load of 7.776 kN and impact energy of 16 J obtained in the weld made at 1200 rpm using triangular pin tool. The welds made at 800 rpm had lowest impact energy. The lowest hardness values found in the heat affected zones of the welds. Circumferential fracture mode for conical pin tool welds and nugget pull-out fracture mode for triangular pin tool welds observed after tensile tests.

Effects of various tool plunge depths on microstructure evolution, mechanical properties and dome structure features of friction stir spot welded AA5052‐H32 similar joints

AbstractThe solid‐state nature of friction stir spot welding process provides outstanding advantages for the sound joining of aluminum alloys. Within this study, 3 mm‐thick AA5052‐H32 sheets are successfully joined by friction stir spot welding using 2344 hot‐worked steel pin to investigate the effects of various tool plunge depths on the microstructure, mechanical and metallurgical properties of similar welds. Therefore, the experiments are performed at different plunge depths in the range of 3 mm–4 mm. Accordingly, the relationships between the process parameter (tool plunge depth) and the responses (microstructure, dome structure, microhardness and lap shear tensile load) are established. Microstructure analyses demonstrate that the increase in the plunge depth leads to more grain refinement within the stir zone, which significantly affects the mechanical performance of the similar joints. This study also indicates that the tool plunge depth in friction stir spot welding process has a noteworthy influence on the characteristic features of the 5052 aluminum alloy joints, such as the dome structure. Moreover, an explicit increase in the microhardness towards the weld stir zone is observed in all specimens. It is found that the average maximum tensile‐shear force enhances with the increment in the tool plunge depth from 3 mm to 4 mm.