Optimization of process parameters of friction stir spot welding of polycarbonate sheets and morphological analysis

Friction stir spot welding has a great impact on the joining process of thermoplastics. In this work, effects of varying rotational speed, plunge depth, and dwell time were investigated on polycarbonate sheets and a filler sheet was utilized to reduce the keyhole size of friction stir spot welded joints. The welding parameters were arranged according to Taguchi L₉ orthogonal design of experiments to determine the optimum levels of process parameters. Lap shear tests were performed to examine the mechanical properties. Using analysis of variance and signal to noise ratio, influences of each welding parameter on the lap joint shear load were evaluated. According to achieved results, tool rotational speed has the highest effect while plunge depth has minimum effect on the mechanical behavior of friction stir spot welded joints. Optimum process parameters were attained as 1000 min⁻¹ for rotational speed, 10.5 mm of plunge depth, and 40 s of dwell time. Optimized process parameters showed 15 % improvement compared to the initial welding parameters. Cross-sectional appearances of welded samples which play an important role in determining lap joint shear load were analyzed by morphological and visual comparisons. Failure modes of the fractured samples for lowest, moderate and highest lap joint shear loads were also observed.     

Effect of friction stir welding process parameters on the tensile strength of dissimilar aluminum alloy AA2024-T3 and AA7075-T6 joints

This work investigates the influence of friction stir welding parameters on the mechanical properties of the dissimilar joint between AA2024-T3 and AA7075-T6. Experiments are conducted consistent with the three-level face-centered composite design. Response surface methodology is used to develop the regression model for predicting the tensile strength of the joints. The analysis of variance technique is used to access the adequacy of the developed model. The model is used to study the effect of key operating process parameters namely, tool rotation speed, welding speed and shoulder diameter on the tensile strength of the joints. The results indicate that friction stir welding of aluminum alloys at a tool rotation speed of 1050 min⁻¹, welding speed of 40 mm/min and a shoulder diameter of 17.5 mm would produce defect less joint with high tensile strength.     

Optimization of dry sliding wear parameters of AA336 aluminum alloy-boron carbide and fly ash reinforced hybrid composites by stir casting process

Boron carbide (10 wt%) and fly ash (5 wt%) particles are reinforced in AA336 aluminium alloy by stir casting process. Microstructure of samples are investigated and dry sliding wear factors viz., load (10 N–50 N), sliding distance (500 m–2500 m) and sliding velocity (1 ms⁻¹–5 ms⁻¹) are considered. Response surface methodology is used to design the experiments and wear weight loss of samples is measured. Regression equation is developed to predict the weight loss. Analysis of variance, significance test and confirmation test are used to find the significant wear parameters which affects the weight loss and the wear factors are optimized for obtaining lowest weight loss. Microstructure of samples showed uniform dispersion of particles in AA336 aluminium alloy. Wear test results showed that weight loss increased with increasing load and sliding distance. However, weight loss of samples decreased with increasing sliding velocity. Optimum dry sliding wear factors are found to be a load of 18.1 N, sliding distance of 905.4 m with a sliding velocity of 4.18 ms⁻¹.     

Impact of tool profile on mechanical behavior and material flow in friction stir welding of dissimilar aluminum alloys

The tool pin geometry used in friction stir welding of any material affects the transportation and mixing of the materials at the joint interface during the welding process. This further affects the mechanical properties of the joint. Tapered threaded and unthreaded tool pin profiles were investigated in this research work. The relationship between the material mixing characteristics and mechanical properties of each pin profile were evaluated. The results indicate that more materials mixing occurred in the nugget zone of the welds at lower rotational speed with the threaded tool pin than the unthreaded tool pin. However, at medium rotational speed, more volume of materials was swept into each other better in the unthreaded tool pin than the threaded pin. The tensile strengths of welds with the threaded tool pin were higher than the unthreaded tool pin. Although the two tool pins exhibit similarities in hardness variations across the weld zones however, higher average values of hardness were obtained at the nugget zone for welds performed with the tapered threaded tool pin. These could be as a result of better material mixing and higher opposition to grain dislocations across the dividing lines in the welds from the threaded tool pin.     

Mechanical performance optimization of similar thin AA 7075-T6 sheets produced by refill friction stir spot welding

Refill friction stir spot welding was applied to weld similar thin AA 7075-T6 aluminum alloy sheets in a spot-like joint configuration without a keyhole. The welds were produced using a small tool consisting of sleeve and probe with diameters of 6 mm and 4 mm, respectively. Design of experiment was employed to optimize the welding parameters in terms of the cross tensile strength by using Box Behnken Design. Based on analysis of variance, it can be concluded that plunge depth strongly affects the mechanical performance of the weld. Optimal welding parameters in terms of rotational speed, plunge depth and speed are identified to reach a cross tensile strength of up to 660 N.     

Fatigue performance of friction stir welded Al2024 alloy in a different corrosive environment

The study examines the corrosion fatigue behavior of friction stir welded Al2024 alloy in the corrosive medium. The fatigue tests are conducted at a stress ratio of -1 in the different corrosive medium. The decrease in the fatigue life of welded joints in the corrosive environment is attributed to an increase in the crack initiation susceptibility in the presence of corrosive media. The fractured surfaces are investigated using the scanning electron microscopy (SEM). The formation of the corrosive compounds was studied using x-ray diffractometry.     

Analysis of process parameters effects on friction stir welding of dissimilar aluminum alloy to advanced high strength steel

Thin sheets of aluminum alloy 6061-T6 and one type of Advanced high strength steel, transformation induced plasticity (TRIP) steel have been successfully butt joined using friction stir welding (FSW) technique. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Intermetallic compound (IMC) layer of FeAl or Fe₃Al with thickness of less than 1 μm was formed at the Al–Fe interface in the advancing side, which can actually contribute to the joint strength. Tensile tests and scanning electron microscopy (SEM) results indicate that the weld nugget can be considered as aluminum matrix composite, which is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetallic layer or simply intermetallic particles. Effects of process parameters on the joint microstructure evolution were analyzed based on mechanical welding force and temperature that have been measured during the welding process.     

Testing and modeling for the tensile strength of nylon badminton string at different processing conditions

Nylon is a thermoplastic engineering material widely used in several applications. But to increase the application of nylon in sports, the focus of this work was to optimize the tensile strength of nylon for badminton string. In particular, the testing conditions (temperature, relative humidity and tensile rate) were investigated. The results obtained showed that increasing the processing temperature and humidity both had a negative effect on tensile strength, while increasing the tensile rate had a positive effect. Then, a mathematical model to predict the tensile strength was established by using a response surface methodology and the optimal conditions were verified to validate the parameters. Furthermore, an analysis of variance was used to determine the significant effect of each term on the final response. Based on the results obtained, it was found that the optimum processing temperature is 2.9 °C with a relative humidity of 0 % when the tensile rate is 60 mm/min.     

Effect of tool geometry and process condition on static strength of a magnesium friction stir lap linear weld

Friction stir lap linear welding is conducted on overlapped AZ31 magnesium plates with different welding tools. Welds are made mainly with the orientation such that the weld retreating side on the upper plate is to be placed under load. Welding tools consist of a concave shoulder and a pin having a cylindrical, or triangular, or pie shape. This work addresses the effects of tool geometry and process condition on lap shear strength of welds. The shape of the hook formed due to upward bending of the plate interface on the retreating side and the strength of friction stir processed material are quantitatively characterized. Compared to the cylindrical tool, the triangular tool effectively suppresses the hook on the retreating side due to enhanced horizontal material flow. This primarily leads to a 78% increase in optimized weld strength. A ‘pure’ shear surface present on the tool pin significantly reduces weld strength.     

Effects of rotation speed and dwell time on the mechanical properties and microstructure of dissimilar aluminum-titanium alloys by friction stir spot welding (FSSW)

In this study, the effects of rotation speed and dwell time on the mechanical properties and microstructure of friction stir spot welded joints of dissimilar aluminum and titanium alloys were investigated. Aluminum AA6061 and titanium Ti-6Al-4 V alloys were selected as the work piece. The joint quality, mechanical behavior, and microstructural evolution in the welded regions were considerably affected by the welding parameters. The results of scanning electron microscopy showed the formation of Ti₃Al intermetallic compounds near the thermomechanical affected zone, which significantly affected the properties of the welding joint. Maximum tensile shear load was produced at 1000 min⁻¹ and 10 s dwell time. Moreover, the welding joint microhardness was improved with increasing the rotation speed.     

Effect of friction stir welding on the microstructure and mechanical properties of AA 6063-T6 aluminum alloy

In this study, AA 6063-T6 alloy plates were joined via friction stir welding using three different pin geometries (i. e., helical threaded, pentagonal and triangular) under various process parameters of tool rotational speed and welding speed. The microstructures and mechanical properties of the various welded joints were investigated. Macro-structural observations revealed that kissing bonds occurred in the welded joints due to fractured oxide layers. X-ray diffraction analysis indicated that the stir zones of the welded joints exhibited phases of Al₈Fe₂Si, Al₅FeSi, and Mg₂Si. In the welded joints, processed using a helical threaded pin, no tunnel-type defect was detected to occur; specimens were fractured outside of the joint region during tensile tests, indicating that the kissing bonds formed in the stir zones did not cause any deterioration in tensile strength or ductility. The welded joints processed using a helical threaded, pentagonal and triangular pin at 500 min⁻¹ tool rotational speed and 80 mm min⁻¹ welding speed exhibited a ductile deformation behavior along with a tensile strength in the range of 153 MPa to 155 MPa.     

Role of plunge depth on the joint formation and mechanical behavior of Al6063-AZ91 dissimilar lap joint produced by friction stir welding

Dissimilar lap joint of Al6063 aluminium and AZ91 magnesium alloys was successfully produced by friction stir welding. Three different plunge depths (3.2 mm, 3.25 mm, and 3.3 mm) were adopted during welding. Similar Al6063–Al6063 lap joints were also produced along with the dissimilar Al6063–AZ91 joints for the purpose of comparing the joint formation. With the increased plunge depth, the width of the similar Al6063 - Al6063 lap joint was increased. On the contrary, joint width was decreased for the dissimilar joint with increased plunge depths. The dissimilar joint was formed with a strong metallurgical bonding between the Al6063 and AZ91 alloys, which is attributed to the mechanical mixing of these alloys in the nugget zone. Additionally, the formation of intermetallics was also observed from the x-ray diffraction analysis. The variations within the measured hardness values were higher at the joint interface due to the mixing of aluminium and magnesium alloys in the nugget zone. From the tensile shear tests, increased strength and decreased elongation were measured with the increased plunge depth. The results demonstrate the importance of the plunge depth on the lap joint formation between dissimilar Al6063–AZ91 alloys during friction stir welding.     

The influence of coefficient of friction in thermal prediction of refill friction stir spot welding process of AA7075-T6

Numerical modelling of refill friction stir spot welding helps in the deep investigation of physics involved in the joining process. The current study investigates four variants of contact models and their influence on thermal prediction in the process. The contact models with constant shear and coulomb friction coefficients and temperature-dependent shear and coulomb friction coefficients were used in the numerical models to investigate the influence of friction coefficients in the prediction of thermal cycles in refill friction stir spot welding. The results from the numerical model are compared and validated with the experimental results from a previous study. The contact model with temperature-dependent coulomb friction coefficient was concluded to be more reliable when compared to the other three contact models. The temperature for this contact model at the centre of the weld is 505 °C, which differs from the temperature recorded in the experiment by 2 %. The peak temperatures of numerical models with constant coulomb and shear friction coefficients differ from the experimental temperature at the weld centre by 5.17 % and 16.8 % respectively.     

Performance optimization of polyetherimide-zeolite 4A mixed matrix membranes for carbon dioxide/methane separation process using response surface methodology

The performance optimization studies of zeolite 4A embedded polyetherimide mixed matrix membranes to separate carbon dioxide/methane by simultaneously considering the effect of process parameters on process responses were the focus of this study. Mixed matrix membranes were characterized and analyzed. The thermophysical characteristics of the synthesized membranes were assessed by different analytical equipment. The permeability of pure gases was determined at varying feed pressures (4 bar to 10 bar) to evaluate gas separation performance. Process optimization studies were accomplished by response surface methodology to find the relation of pressure and zeolite loading on carbon dioxide and methane permeability, and carbon dioxide/methane selectivity. The characterization results revealed that all membranes were dense in structure and has improved thermal stability. The spectrometry results confirmed the molecular interaction between polyetherimide and zeolite 4A filler. Gas permeability results showed a more than 90 % increase in carbon dioxide permeability compared to the nascent polyetherimide membrane. Similarly, selectivity of mixed matrix membranes was 45 % higher than polyetherimide membrane. The optimal operating conditions were found to be 20 wt. % zeolite loading and 6 bar pressure with overall desirability of 0.700. These membranes can find potential in various gas separation applications.     

Microstructure and fatigue performance of friction stir welded joints of 2A12-T4 and 7075-T6 dissimilar aluminum alloy

The objective of this work is to investigate the microstructure and fatigue performance of friction stir welding joint of 2A12-T4 and 7075-T6 dissimilar aluminum alloy. Microstructure shows that the grain growth of heat-affected zone in both sides of joint is noticeable; the grain size of thermo-mechanically affected zone in both sides of joint is deformed and distorted in various degrees; nugget zone is fine equiaxed grain with uniform distribution. Microhardness of joint presents an approximate “W” types distribution on the whole, and the highest hardness value of the joint appears near the center of nugget zone, up to 146.5 HV0.2. Since the joint has the higher the fatigue strength ratio, and the S−N curve of the joint shows a smaller downward trend, the joint has the best fatigue performance and 7075-T6 base metal has the worst fatigue performance. Linear fitting of 7075-T6 base metal is ; linear fitting of 2A12-T4 base metal is ; linear fitting of joint is . The fracture analysis presents that the low-cycle fatigue fracture mechanism of welding joint is quasi-cleavage fracture, and the main mode of high cycle fatigue fracture is the inter crystalline fracture, mixed with ductile fracture.     

Different reinforcement strategies of hybrid surface composite AA6061/(B4C+MoS2) produced by friction stir processing

Aluminum surface composites have gained huge importance in material processing due to their noble tribological characteristics. The reinforcement of solid lubricant particles with hard ceramics further enriches the tribological characteristics of surface composites. In the current study, friction stir processing was chosen to synthesize hybrid surface composites of aluminum containing B₄C and MoS₂ particles with anticipated improved tribological behavior. B₄C and MoS₂ powder particles in 87.5: 12.5 ratio were reinforced into the AA6061 by hole and groove method. Microstructural observations indicated that reinforcement particles are well distributed in the matrix. The hardness and wear resistance of hybrid surface composites improved as compared to the base material, due to well distributed abrasive B₄C and solid lubricant MoS₂ particles in AA6061. The hybrid surface composites achieved ∼32 % increased average hardness as compared to the base material. Hole method revealed ∼13 % better wear resistance compared to the groove method for friction stir processed hybrid surface composite, attributing to an improved homogeneity of particle distribution shown by zigzag hole pattern. Moreover, friction stir processed AA6061 without reinforcement particles exhibited reduced hardness and wear resistance due to loss of strengthening precipitates during multi-pass friction stir processing.     

Influence of tool geometry and rotational speed on mechanical properties and defect formation in friction stir lap welded 5456 aluminum alloy sheets

Friction stir welding of AA5456 aluminum alloy in lap joint configuration is with two different tempers, T321 and O, and different thicknesses, 5 mm and 2.5 mm was investigated. The influences of tool geometry and various rotational speeds on macrostructure, microstructure and joint strength are presented. Specifically, four different tool pin profiles (a conical thread pin, a cylindrical–conical thread pin, a stepped conical thread pin and Flared Triflute pin tool) and two rotational speeds, 600 and 800 rpm, were used. The results indicated that, tool geometry influences significantly material flow in the nugget zone and accordingly control the weld mechanical properties. Of particular interest is the stepped conical threaded pin, which is introduced for the first time in the present investigation. Scanning electron microscopy investigation of the fracture location of samples was carried out and the findings correlated with tool geometry features and their influences on material flow and tension test results. The optimum microstructure and mechanical properties were obtained for the joints produced with the stepped conical thread pin profile and rotational speed of 600 rpm. The characteristics of the nugget zone microstructure, hooking height, and fracture location of the weld joints were used as criteria to quantify the influence of processing conditions on joint performance and integrity. The results are interpreted in the framework of physical metallurgy properties and compared with published literature.     

Electrochemical performance in seawater and microstructural evolution of friction stir welded joints of dissimilar AA1050 and AZ91D

This paper presents the electrochemical performance and microstructural evolution of friction stir welded joint of dissimilar AA1050 and AZ91D in seawater, for potential applications in the transportation industry. The corrosion behavior of the dissimilar weld was compared to the corrosion behavior of the parent materials, and similar welds of each alloy. The experiments were successfully conducted with an H13 hot-working tool steel in butt-joint configuration. The results revealed the presence of intercalated microstructure in the dissimilar weld and homogenous microstructures in the similar welds. The corrosion resistance properties of the parent materials and similar welds were higher than that of the dissimilar weld sample. The dissimilar weld has a current density of 3.83×10⁻⁵ A/cm² and corrosion rate of 9.99×10⁻⁴ mm/year; and is most susceptible to corrosion, due to the galvanic coupling between the dissimilar alloys and intermetallic compounds. The similar weld of AA1050 has a current density of 1.99×10⁻⁷ A/cm² and corrosion rate of 1.44×10⁻³ mm/year, while the similar weld of AZ91D has a current density of 8.58×10⁻⁶ A/cm² and corrosion rate of 1.13×10⁻¹ mm/year.     

Modeling and prediction of weld shear strength in friction stir spot welding using design of experiments and neural network

Friction Stir Spot Welding (FSSW) is a kind of the friction stir welding (FSW) process, creates a spot, lap‐weld without bulk melting work materials. The tensile shear strength of the FSSW welded joints mainly depends on the pin height, tool rotation and welding time. In the present study, two of the techniques, namely factorial design and neural network (NN) were used for modeling and predicting the tensile shear strength of EN AW 5005 aluminum alloy. Tensile shear strength was taken as a response variable measured after welding pin height, tool rotation and welding speed were taken as input parameters. Relationships between tensile shear strength and welding parameters have been investigated. The level of importance of the FSSW parameters on the tensile shear strength was determined by using the analysis of variance method (ANOVA). The mathematical relation between the tensile shear strength and FSSW welding parameters were established by regression analysis method. This mathematical model may be used in estimating the tensile shear strength of FSSW joints without performing any experiments. Finally, predicted values of tensile shear strength by techniques, NN and regression analysis, were compared with the experimental results and their nearness with the experimental values assessed. Results show that, NN is a good alternative to empirical modeling based on full factorial design.     

Thermal analysis of friction stir processing (FSP) using arbitrary Lagrangian-Eulerian (ALE) and smoothed particle hydrodynamics (SPH) meshing techniques

Friction stir processing (FSP), a derivation of friction stir welding (FSW) is a material processing method which is used to locally modify the microstructure and texture of a given material. In friction stir processing (FSP), the heat produced by the frictional force and material deformation plays a significant role in producing a good surface quality. Therefore, the thermal modeling of friction stir processing (FSP) requires accurate boundary conditions and an appropriate mesh modelling technique. In this study, the thermal behavior of friction stir processing (FSP) using the aluminum alloy 6061-T6 for different process parameters is investigated. To solve complicated governing equations, two finite element formulations have been utilized; i. e. an arbitrary Lagrangian-Eulerian (ALE) and a smoothed particle hydrodynamics (SPH). For the arbitrary Lagrangian-Eulerian (ALE), a three-dimensional (3D) fully coupled thermomechanical finite element model using a modified Coulomb friction and Johnson-Cook material law has been used. The results show that, the temperature behavior is asymmetrical in the cross section and the peak temperature is approximately around 60 %–80 % of the melting temperature of the AA6061-T6. Moreover, it is seen that as the rotating velocity increases, the peak temperature is also increased; and the peak temperature decreases as the transverse speed increases. Finally, a good correlation between the calculated values and the literature is found.