Increase In Tool Rotational Speed Research Articles

Mechanical and microstructural characterisation on the effect of increasing tool rotational speed of friction stir welded AZ31-B magnesium alloy

ABSTRACT This article intends to deliver the mechanical and microstructural characterisation of the impact of increasing the tool rotational speed on friction stir-welded similar AZ31-B magnesium alloy. The variable tool rotational speeds of 1000, 1200, 1400, and 1600 rpm with a fixed tool traverse speed of 30 mm/min were chosen based on the trail welding method. The macrostructural examination reveals that the lower tool rotational speed of 1000 rpm produced micro tunnel defects due to insufficient heat input, which causes less material intermixing. The microstructural examination shows finer grain size values when increasing the tool's rotational speed for 1000 rpm (12.5μm), 1200 rpm (9μm), 1400 rpm (7μm), and 1600 rpm (7.6μm). The tool rotational speed of 1400 rpm produced a defect-free welded joint with a higher tensile strength value of 215 MPa and a higher hardness value of 74 HV. Fractography analysis reveals all four welded samples were ductile fractured at an angle of 450. The higher welded joint efficiency of 78% was attained at the 1400 rpm welded parameters and the lower efficiency of 48% was achieved at the tool rotational speed of 1000 rpm.

Thermal and mechanical characterisation of friction stir welded dissimilar aluminium alloys

The influence of thermal properties on the friction stir welded (FSW) dissimilar aluminium alloys at different tool rotational speeds and tool pin profiles was studied. AA 5083 H111 and AA 6082 T6 of 6 mm aluminium alloy plates are welded by varying the process parameters. The influence of heat generation and heat transfer in the joint efficiency of the weldments are characterised. Heat flow and heat flux for various tool rotation speeds generated between the tool shoulder and workpiece are calculated and analysed. The rate of heat distribution during welding is evaluated by calculating the thermal diffusivity of AA5083 H111 and AA6082 T6. Microhardness test helps to comprehend the influence of the parameters over the mechanical property of the weldments. The results revealed that the thermal characterisation clearly illustrates that an increase in tool rotation speed directly amplifies the heat flow and heat flux in weldments. However, AA 5083 H111 and AA 6082 T6 for varying temperature and reveals that 580°C possessed higher thermal conductivity for AA 6082 T6 (260 W/m°C) and AA 5083 5083 H111 (160 W/m°C), thermal conductivity for AA 6082 T6 (1260 J/Kg°C) and AA 50835083 H111 (1225 J/Kg°C) and thermal Diffusivity was 5.2029 × 10−5 (m2/s) for AA 5083 H111 and 7.61819 × 10−5 (m2/s) for AA 6082 T6.

Influence of tool rotational speed on mechanical and corrosion behaviour of friction stir processed AZ31/Al2O3 nanocomposite

Nano-sized reinforcements improved the mechanical characteristics efficiently by promoting more implicit particle hardening mechanisms compared to micron-sized reinforcements. Nano-sized particles lessen the critical particle solidification velocity for swamp and thus offers better dispersal. In the present investigation, the friction stir processing (FSP) is utilized to produce AZ31/Al2O3 nanocomposites at various tool rotation speeds (i.e., 900, 1200, and 1500 rpm) with an optimized 1.5% volume alumina (Al2O3) reinforcement ratio. The mechanical and corrosion behavior of AZ31/Al2O3-developed nanocomposites was investigated and compared with that of the AZ31 base alloy. The AZ31 alloy experienced a comprehensive dynamic recrystallization during FSP, causing substantial grain refinement. Grain-size strengthening is the primary factor contributed to the enhancement in the strength of the fabricated nanocomposite. Tensile strength and yield strength values were lower than those for the base metal matrix, although an upward trend in both values has been observed with an increase in tool rotation speed. An 19.72% increase in hardness along with superior corrosion resistance was achieved compared to the base alloy at a tool rotational speed of 1500 rpm. The corrosion currents (Jcorr) of all samples dropped with increase in the rotational speed, in contrast to the corrosion potentials (Ecorr), which increased. The values of Jcorr of AZ31/Al2O3 were 42.3%, 56.8%, and 65.5% lower than those of AZ31 alloy at the chosen rotating speeds of 900, 1200, and 1500 rpm, respectively. The corrosion behavior of friction stir processed nanocomposites have been addressed in this manuscript which has not been given sufficient attention in the existing literature. Further, this work offers an effective choice for the quality assurance of the FSP process of AZ31/Al2O3 nanocomposites. The obtained results are relevant to the development of lightweight automobile and aerospace structures and components.

Mechanical Properties and Corrosion Characteristics of Dissimilar Friction Stir Welded AA1000/AA6061-T6 Aluminum Alloys

This paper is aimed to investigate microstructure, corrosion and mechanical properties of dissimilar metal weld joints between AA1000 and AA6061-T6 under different tool rotational speeds of 910, 1500, and 2280 rpm at a constant transverse speed of 30 mm/min. Several experimental works have been conducted including microstructure observation using optical microscopy and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS), Vickers microhardness measurements, tensile tests, and corrosion measurements using Potentiodynamic Polarization method. Results show that increasing tool rotational speed from 910 rpm to 1500 rpm increases the degree of homogeneity in nugget zone and improves strength of the weld joint but further increase in the tool rotational speed up to 2280 rpm degrades the mechanical properties due to coarsening of the microstructure. Furthermore, corrosion rate of the nugget zone (NZ) is in between the two base metals.

Material flow and channel geometry evolution during friction stir channeling process – Impact of tool geometry and process parameters

The capability of manufacturing controlled and uniform geometry of channels is critical for potential application of friction stir channeling in thermal systems. The channel geometry is governed by the material flow around the tool during the channeling process. The heat generation and material flow are closely dependent on the friction stir channeling parameters (tool geometry and process parameters). In the present investigation the interrelation between the friction stir channeling parameters with material flow and channel geometry is analysed. The channel geometry is found to be function of tool geometry for constant process parameters. The channel area and height increase with reduction in the pin diameter, the shoulder diameter and with increase in the pin length. The process parameters govern the channel geometry for constant tool geometry. The increase in tool rotation speed, and reduction in tool travel speed and shoulder clearance resulted in reduction in channel area and height.

Investigation of weld defects and mechanical properties of dissimilar friction stir spot welded dual phase (DP600) steel and aluminum alloy (AA 7075-T6) plates

DP600 steel and AA7075-T6 aluminium alloy plates were joined using the friction stir spot welding process. The effects of different tool rotational speeds on the mechanical properties, intermetallic compound formation and interface microstructure of welded joints were investigated. The highest lap shear tensile load was obtained from the samples joined at a rotational speed of 1040 rpm (6.5 kN). It was determined that the tensile load of the welded joint decreased with increasing tool rotational speed. XRD analysis performed on broken surfaces, the intermetallic phase was determined to be Al13Fe4. As a result of Vickers microhardness tests, the samples joined at 1320 rpm and 1500 rpm, in the structure of which intermetallic compounds were determined by XRD analysis, displayed higher hardness values. In addition, when scanning electron microscope images were examined, it was determined that the cracks observed in the samples and the porosity both increased with increasing tool rotational speed.

Effects of parameters on friction stir welding process of AA 7075 aluminum alloy: mechanical and microstructural assessments

AbstractThe effect of tool rotation speed and welding speed on the microstructural and mechanical properties of AA 7075‐T651 welded plates produced using friction stir welding is the research subject of this study. A basin‐shaped stir zone characterized all friction stir welded joints’ microstructures. The fracture location following the tensile test was found to be outside the stir zone for each welded joint. All welded joints were subjected to a 90° root bending test. The tests were terminated before each welded joint could reach the 90° bend angle in the stir zone. The stir zone of each welded joint was characterized by the fine and equiaxed grains with the effect of dynamic recrystallization. In addition, intermetallic particles were also detected to occur in the weld joint. Among the nine welded joints, the welded joint with the highest ultimate tensile strength of 382 MPa was produced with a tool rotation speed of 400 min−1 and a welding speed of 80 mm min−1. The highest welding efficiency of 71 % was obtained with the welding process parameters of 400 min−1 tool rotational speed and 80 mm min−1 welding speed. Increasing tool rotation speed caused the grain size to be coarser.

The influence of tool rotation speed on the low-cycle fatigue behavior of AA2519-T62 friction stir welded butt joints

The subject of this study were the friction stir welded butt joints of the 5 mm thick AA2519-T62 alloy obtained with four various values of tool rotation speed: 200, 400, 600 and 800 rpm, and the constant welding velocity of 100 mm/min. The examination involved macro and microstructure observations, microhardness, tensile, and fatigue testing. An increase in the stir zone size and microhardness has been reported together with increasing tool rotation speed. The weld obtained with the lowest value of tool rotation speed (200 rpm) is characterized by a significant reduction of microhardness in the SZ, which makes it very susceptible to plastic deformation. In terms of tensile properties, there is a tendency of increasing welds’ yield and tensile strength together with increasing applied tool rotation speed. The tensile failures occur in the LHZ, which is located, depending on tool rotation speed, at the SZ (200 rpm), at the HAZ/TMAZ interface (400 rpm) or at the SZ/TMAZ interface (600 and 800 rpm). For AA2519-T62 and its FSW joints, the cyclic strain hardening is stronger than monotonic strain hardening. The LCF behavior of the FSW joints have been described by the parameters of the Manson-Coffin-Basquin, taking into account the Smith-Watson-Topper parameter. The established fatigue parameters indicate that the joints produced with the 400–600 rpm tool rotation speed exhibit the lowest reduction in fatigue strength coefficient. The fractured surfaces have a typical fatigue striation pattern with the participation of secondary cracks and small Al2Cu particles.

Microstructure and mechanical performance of dissimilar friction stir spot welded AA2024-O/AA6061-T6 sheets: Effects of tool rotation speed and pin geometry

Nowadays, friction stir spot welding (FSSW) is becoming a serious candidate technology to join aircraft materials such as AA2024-O and AA6061-T6 since the use of FSSW offers significant weight savings compared to a conventional riveting technique. However, some issues, especially related to mechanical properties of FSSW joints still exist. To address these problems, the present investigation aims to study effects of tool rotation speed and pin geometry on microstructure and mechanical strength of dissimilar friction stir spot welded AA2024-O/AA6061-T6 joints. The welding processes were conducted using two different tool pins, namely cylindrical and stepped pins at varying tool rotation speeds of 900 rpm, 1400 rpm and 1800 rpm. Subsequently, experimental works including microstructural observation, microhardness measurements, lap shear tests combined with fractography analysis were conducted. Results showed that an increase in tool rotation speed resulted in microstructural coarsening in stir zone (SZ). In addition, the tool rotation speed together with the pin affected the material flow hence hook characteristics. It was found that the dissimilar friction stir spot AA2024-O/AA6061-T6 welded joint having excellent lap shear failure load (LSFL), typically 4468.4 N was produced using a cylindrical pin at the tool rotation speed of 1400 rpm. Under this lap shear testing, the mode of failure changed from shear to mixed mode failure as the tool rotation speed was increased. It seemed that hook characteristics, grain size and precipitation hardening were the key factors influencing the weld mechanical properties.

Friction stir surface processing of 6061 aluminum alloy for superior corrosion resistance and enhanced microhardness

In the current study, friction stir surface processing (FSSur.P) was carried out to alter the surface microstructure of 6061 aluminum alloy using a pinless friction stir tool. The impact of rising tool rotational speed from 400 to 1200 rpm while keeping tool traveling speed constant at 250 mm/min on surface microstructure, mechanical properties, and corrosion resistance was explored in detail. The microstructural findings revealed a significant reduction in grain size, in addition to a remarkable improvement in microhardness of processed samples. Approximately 44% increase in microhardness, compared to unprocessed counterpart was achieved at the lowest rotation speed. The corrosion behavior of the processed samples as well as the base sample was evaluated after 15 days of exposure to 3.5% NaCl using several electrochemical methods such as potentiodynamic polarization technique (PDP), linear polarization method (LPR) and electrochemical impedance spectroscopy (EIS) approach. All electrochemical techniques results demonstrated an excellent agreement where the unprocessed sample showed poor corrosion resistance with corrosion current density of (Icorr.) of 3.22 μA, whereas the sample processed at the highest tool rotating speed exhibited superior corrosion resistance with Icorr. of approximately 0.057 μA. Based on results it was found that increasing tool rotational speed has minimum effect on grain size, as well as microhardness; with best improvement achieved at lowest rotational speed or minimum heat input. On the other hand, the corrosion resistance was found to improve with increasing tool rotational speed. The use of pinless tool had a great impact on simplifying the process and achieve required surface enhancement without altering the subsurface material.

Characterization of novel molybdenum disulfide and cerium dioxide reinforced hybrid aluminum matrix composites fabricated by friction stir processing

AbstractAluminum matrix composites are widely used for making structural components in the aerospace and automobile industries. In order to sustain the operational demand, excellent anti‐wear and corrosion resistance properties are required in the composites. To achieve this, molybdenum disulfide and cerium dioxide reinforced hybrid aluminum‐based composites are fabricated by friction stir processing at different rotational speed and number of passes. Due to grain refinement and better particle distribution at high rotational speed and 2 pass, tensile strength and microhardness improves by sacrificing ductility. However, deterioration of mechanical properties than the as‐received alloy is evident in all the composites due to dissolvement of strengthening precipitates. With increasing tool rotational speed, severe adhesion type of wear shifts to abrasion wear and the wear resistance also improves. All the composites show similar corrosion behavior as the unprocessed alloy. However, the corrosion parameters such as corrosion potential and corrosion current density were influenced by processing conditions. The composite produced with 1500 min−1 and 2 pass exhibits highest wear and corrosion resistance.

Influence of tool rotational speed on the microstructural characterization and mechanical properties of friction stir welded Al-Si10Mg parts produced by DMLS additive manufacturing process

Present study investigate the joining of precipitation hardened AlSi10Mg alloy, developed using direct metal laser sintering technique of additive manufacturing using friction stir welding. Consequently, three, single-pass, square butt-welded joints were fabricated from 3 mm thick plates of this alloy, using friction stir welding process at different tool rotational speeds (low, medium and high). Each welded joint was fabricated at the same transverse speed of 50 mm/min, H13 tool steel possessing scrolled shoulder and 3° tilt angle. Microstructural observations show a significant grain refinement within the stir zone, which reduced with the increase in tool rotational speed. This variation was accredited to the significant dynamic recrystallization in the weldment, and change in the morphology and size of the Si-particles. The transverse tensile test results show a considerable drop in the joint efficiency of the welds from ≈48% to ≈42% with the increase in tool rotational speed from low to high.

Fatigue strength improvement due to alloying steel weld toes with WC tool constituent elements through friction stir processing

Friction stir processing (FSP) enables surface modifications can likely be applied as a new post-weld treatment for improving fatigue strength. When applying FSP to high-strength materials, tool wear occurring at the interface between the tool tip and the topmost steel layer has been regarded as an unavoidable issue and is related to the tool rotational speed. The present study investigated the relationship between the tool rotational speed and fatigue strength of arc-welded high-strength low-alloy (HSLA) steel joints with weld toes subjected to FSP using a spherical-tip WC tool. FSP was conducted on the weld toe of HSLA steel joints with various tool rotational speeds. Tool wear increased with increase in tool rotational speed, and consequently contents of constituent elements of the WC tool increased in the topmost steel layer of weld toes, leading to large increase in fatigue strength. One reason for the increase with tool rotational speed is significant increase in solid solution hardening due to supersaturated W and C in the topmost steel layer consisting of martensite laths. The hardened topmost steel layer prevented fatigue crack initiation, and the increased fatigue strength depended on the contents of supersaturated W and C. Alloying of the topmost steel layer with tool constituent elements of W and C accompanied with WC tool wear during FSP is unique additive manufacturing to increase the fatigue strength of welded joints, and can be employed locally on structural components susceptible to fatigue.

Comparison of response surface methodology with artificial neural network for prediction of the tensile properties of friction stir-processed surface composites

In the present work, nanoboron carbide is integrated in the aluminum matrix using friction stir processing: by varying process parameters, that is, tool pin profile, tool rotational speed and tool traverse speed, based on Taguchi L16 design of experiment. A self-assembled monolayer is successfully developed on the substrate to homogeneously and uniformly distribute the reinforcement particles. Response surface methodology and artificial neural network models are developed using ultimate tensile strength and total elongation as responses. Percentage absolute error between the experimental and predicted values of ultimate tensile strength and total elongation for the response surface methodology model is 3.537 and 2.865, respectively, and for artificial neural network is 2.788 and 2.578, respectively. For both the developed models experimental and forecasted values are in close approximation. The artificial neural network model showed slightly better predictive capacity compared to the response surface methodology model. From the scanning electron microscopy micrograph, it is evident that throughout the matrix B4C reinforcement particles are well distributed also; with increasing tool rotational speed grain size decreases up to 1200 r/min; on further increasing the tool rotational speed particles starts clustering.

Finite Element Simulation of Friction Stir Welding of Inconel 718 to Nimonic 80A

This paper presents results of simulation of friction stir dissimilar welding of 5 mm thick, Nickel-based super-alloys, Inconel 718, and Nimonic 80A using Abaqus software. Four different trials were done to understand the influence of tool rotation speed on temperature distribution in weld zone while travel speed remains constant. The temperature in the weld zone was found to increase with the increase in tool rotation speed and travel speed. The temperature on the advancing side of the tool was higher than that of the retreating side. The tensile strength of weldment was found, by simulation, to be 25% more than that of base metal, Inconel 718. This may be due to grain refinement and dynamic recrystallization during FSW. The simulated bend test revealed an adequate level of ductility of weldments.

Numerical Simulation for the Optimization of Polygonal Pin Profiles in Friction Stir Welding of Aluminum

The tool with polygonal pin profile has been widely employed in friction stir welding (FSW) of aluminum, but there is hardly an effective optimization methodology existed as the thermomechanical characteristics affected by pins with various flats number have not been understood comprehensively. Therefore, the present work employs a 3-dimensional computational fluid dynamics (CFD) model to have an integrated observation of the FSW process with the effect of polygonal pin profiles. Both the heat generation modes due to contact friction at the tool–workpiece interface and volumetric viscous dissipation in the vicinity of the tool are considered. The model is utilized to give a quantitative analysis of the heat generation, temperature distribution, plastic material flow and welding loads during the FSW process for various tools with polygonal pin profiles, as well as a variety of shoulder diameters, welding speeds and tool rotation speeds. The calculated results of thermal cycles, tool torques and joint cross sections for some typical polygonal pins and welding parameters are all found to be compared well with the experimental ones, which demonstrates the feasibility and applicability of the present numerical model. Particularly, a methodology is developed for the optimization of the flats number by identifying the torque components in both parallel and vertical direction of the pin-side flat region. The results show that the optimized pin flats number increases with increasing tool rotation speed, while the influence of both welding speed and shoulder diameter can be supposed to be insignificant. Moreover, the dependability of the optimized results is also discussed by considering wear tendency and service life of the pin for multiple welding conditions.

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.

Investigations on microstructural and mechanical properties of friction stir welded AA 2024-T351

Abstract In the present study, AA 2024-T351 plates with a thickness of 6 mm were joined using the friction stir welding technique with three different tool rotational speeds and two different pin profiles. Microstructural features and mechanical properties of welded joints were investigated. The grains in recrystallized regions along the stir zone were observed to be almost with invariable sizes. The grain size was revealed to increase with the increase in tool rotational speed. The average grain size was observed to dramatically increase from 2.3 μm to 5.6 μm for welded joints produced with pentagonal shaped pin. All the welded joints were observed to contain defects; the presence of defects exhibited a negative effect on the tensile properties of the welded joint. Most of the defects were observed to localize at the root region of joints. The joint, welded with the tool rotational speed of 250 rpm using pentagonal shaped pin, exhibited ultimate tensile strength with a value of 365 MPa. The ultimate tensile strength of welded joints was found to be higher with the decrease in the tool rotational speed. The welding efficiency of joints was compared with the ultimate tensile strength of base metal; notably, welding efficiency values between 46 % and 80 % were achieved. Microstructural characterizations revealed that Al2Cu (θ phase), Al2CuMg (S phase), and AlCuFeMnSi, Al7Cu2Fe intermetallic particles were dispersed in the stir zone.

Elucidation of interfacial microstructure and properties in friction stir lap welding of aluminium alloy and mild steel

The rate of heat generation and plastic deformation of materials should be precisely controlled in order to get a strong and sound weld joint during dissimilar friction stir lap welding (FSLW) of aluminium and steel. The effect interfacial microstructure at the weld joint interface on mechanical properties is elucidated in the present investigation with the help of detailed microstructure evaluation in FSLW of AA6061 and mild steel (MS). The results indicated a substantial variation in interfacial structure from formation of a bi-metallic straight interface, intercalated structure to mechanically mixed zone (MMZ) with the increase in tool rotation speed from 300 rpm to 1700 rpm. In addition, significant differences in the microstructure evolution mechanisms were noticed from the AA6061 side to MS side through the interfacial microstructure. The variation in interfacial structure and corresponding change in the fracture location predominantly affected the mechanical properties of the joints at different tool rotation speeds. The fracture locations in MMZ and intercalated structure showed the highest and lowest lap shear strengths, respectively.

Analysis of micro-friction stir welding surfaces using fractal methodologies

The weld surface produced by micro-friction stir welding (micro-FSW) exhibit multi-scale nature. The surface topography of weld surfaces affects the overall strength of components and significantly changes with process parameters. In this work, multi-scale surface characterization techniques are used to study the surface topography of micro-FSW surfaces. The relation between process parameters and topography parameters is discussed in detail. Length-scale fractal analysis is employed on micro-FSW surfaces, and it is concluded that surface complexity increases with an increase in tool rotational speed. Within the range of process parameters studied, smoothening takes place at higher tool feed. The Hurst coefficient (H), which is an important descriptor of fractal geometry is found to increase with an increase in tool feed.