A Multi Response Optimization of Tool Pin Profile on the Tensile Behavior of Age-hardenable Aluminum Alloys during Friction Stir Welding

The main aim of this study is to select a suitable tool pin profile to maximize the tensile behavior (Ultimate Tensile Strength and Tensile Elongation) of Friction stir welded aluminum alloys of AA 2024 and AA 6061. The age-hardnable aluminum alloys of 2xxx, 6xxx and 7xxx series are extensively used in automobile and aircraft industries because of its high strength to weight ratio, formability and ductility. These alloys are vulnerable to cracking (2xxx and 7xxx) and highly melt (6xxx) in conventional fusion welding techniques. Friction stir welding is an emerging solid state welding technique which is best suitable for joining these aluminum alloys. The influential process and tool parameters that are affecting the FS welded joints are such as tool rotational speed, welding speed, axial load and tool pin profile. Dissimilar friction stir welded joints of AA 2024 and AA 6061 aluminum alloys are fabricated using a friction stir welding process to examine the influence of the tool pin profiles on tensile properties on various crucial process parameters. A Box-Behnken design with four input parameters, three levels and 30 runs is used to conduct the experiments and Response Surface Method (RSM) is used to develop the mathematical model. The experimental results were predicted at the 95% confidence level. The macro defects in the welds and the modes of tensile fracture are discussed in detail to reveal the root cause of failure in the fabricated samples. The rotating tool equipped with a square pin generated the highest ultimate tensile strength (143 MPa) with a 12% elongation. A microstructure variation on dissimilar alloys which result 44% reduction in tensile strength on AA2024 and 51% reduction in tensile strength on AA6061 aluminum alloys was observed on the stir zones.


INTRODUCTION
The conventional fusion welding techniques such as arc, gas welding of age hardnable aluminum alloys (2xxx, 6xxx and 7xxx) are a challenging task for designers and technologists.Since, the difficulties in the fusion welding process are associated mainly related to the presence of the oxide layer, solidification shrinkage, high coefficient of thermal expansion, high thermal conductivity and other gases in a molten state (Shanmuga Sundaram and Murugan, 2010).Joining these alloys using fusion welding techniques leads to the melting and re-solidification of the fusion zone, results the formation of brittle inter-dendritic structure and eutectic phases.The formation of brittle structure in the weld zone results a drastic loss of mechanical properties (Rhodes et al., 1997;Su et al., 2003).Generally, aluminum alloys of AA 2024 (Al-Cu alloy) extensively used for aerospace applications because of its high strength to weight ratio however these alloys are classified into non weldable since these alloys are sensitive to cracking (Shanmuga Sundaram and Murugan, 2010) due to its copper alloying element.The heat provided in fusion welding decay the mechanical properties lead phase transformation and softening the fusion zone is significant.Few 2xxx grades of aluminum alloys can be resistance welded but surface preparation is expensive.Aluminum alloys of AA 6061 (Al-Mg-Si) are mainly used for commercial applications of marine and automotive fittings, bicycle frames etc.These AA 6061 aluminum alloys can be welded using TIG, MIG welding however, losses of mechanical properties near the fusion zone are significant.Therefore, fusion welding techniques are not suitable for the dissimilar welding of aluminum alloys AA 2024 and AA 6061, therefore friction stir welding process could be the best for the dissimilar welding of these alloys.
Friction Stir Welding (FSW) was invented in December 1991 by Wayne Thomas and a team of his colleagues at The Welding Institute UK (Thomas et al., 1991;Dawes and Thomas, 1995).It is an innovative and emerging technique in the solid state welding.A non consumable steel tool rotates around its axis to the abutting edge of the plates and the heat is generated as a result of the contact between the surfaces of the tool and work piece.Compared to other welding techniques, FSW offers many advantages, such as low residual stresses, little distortion; high joint strength and bulk melting are avoided (Dawes and Thomas, 1995).Friction stir welding immune defects and deteriorations associated with the fusion welding are limited.Addition to that, the extensive thermo mechanical deformation induces dynamic re-crystallization that refines the micro structure on FS welded region therefore mechanical properties are improved such tensile strength, hardness etc.
Numerous numbers of studies have been performed and imparted significance of dissimilar joining of aluminum alloys of friction stir welding.Hu et al. (2012) investigated the tensile deformation characteristics of AA 2024 aluminum alloys.It is reported that, the FS welded joint has diverse characteristics on tensile deformation leading significant reduction in global ductility.Mohammadtaheri et al. (2013) investigated the effects of base material conditions on the friction stir welding of AA 2024 aluminum alloys.It was found that, the average grain sizes of base material and stirred zone are almost identical.Da Silva et al. (2011) evaluated the joining parameters of AA 2024 aluminum alloys using friction stir welding to understand the mixing process and identified no material mixing was attained however a fine grained stirred zone was observed on the micro structural observation.Ying et al. (2000) reported in their study on friction stir welding of AA 2024 to silver.It is reported, the age hardenable aluminum alloys (2xxx, 6xxx, 7xxx series) are suffer strength degradation due to microstructure variation during mixing especially, in the narrow regime just outside the FSW zone.Ouyang and Kovacevic (2002) investigated the material flow and microstructure in the friction stir welded butt joints of same and dissimilar aluminum alloys of AA 6061 and AA 2024.It is reported in this study, there is a substantial variation in hardness throughout the nugget zone.Addition to that, the degree of mixing, material flow patterns are associated with the process parameters.Therefore, suitable parameters are supposed to provide to obtain a significant joint strength of the weld joints.The important process and tool parameters that are affecting the joint strength of FS welded joints are rotational speed (N), the welding speed (F) axial load (P) and pin profiles such as cylindrical, square, tapered and hexagonal.These parameters are vital for the material flow pattern, the mechanical and metallurgical transformation and the temperature distribution of the weld joints.The effects of the tool pin have been investigated by varying the tool pin profile on various aluminum and its alloys (Kwon et al., 2012;Dehghani et al., 2013).In those investigations are demonstrated using mathematical and statistical approaches.The mathematical approaches that are commonly used to select the process parameters are time consuming, requiring extensive resources to obtain a feasible solution (Lakshminarayanan and Balasubramanian, 2008).Therefore, these types of complex problems can be solved using statistical techniques.Especially when the responses have diversity then the multi objective optimization techniques are applied.Sefika (2013) used taguchi based grey relational analysis to improve the ultimate tensile strength and elongation of friction stir welded AA6082-T6/AA5754-H111 aluminum alloys.Elmesalamy et al. (2013) used response surface methodology to understand the process parameter selection for laser welding process.Muhammad et al. (2013) used Taguchi based response surface methodology to develop the quality features of resistance spot welding technique.Anish et al. (2013) applied response surface methodology for setting the optimal input process parameters for the WEDM process.Exclusively, in friction stir welding; Rajakumar and Balasubramanian (2012) used desirability approach to optimize the AA1100 aluminum alloy using friction stir welding technique, Lakshminarayanan and Balasubramanian (2008) used response surface technique to optimize the process parameters of AA7039 aluminum alloy joints, Karthikeyan and Balasubramanian (2010) predicted optimized welding parameters for joining AA2024 aluminum alloy using response surface methodology.Therefore, numerous investigations reveal the various statistical methodologies for obtaining the suitable parameter selection when the diversified objective; however, those investigations are not discussing about dissimilar FS welding of AA2024 and AA6061 aluminum alloys.Hence, in this present investigation, a multi response optimization approach called response surface method using desirability function is applied in order to maximize the ultimate tensile strength and tensile elongation of age hardnable aluminum alloys of AA6061-AA2024.
Experimental setup: A home-built FSW machine was used to fabricate the weld joints.A schematic arrangement for the aluminum alloy plate during the welding process is shown in Fig. 1.AA2024-T3 and AA6061-T6 aluminum alloys are selected for the dissimilar FS welding process.T3 represents the AA2024 alloy, which is solution heat-treated, coldworked and naturally aged to a substantially stable condition.To improve strength, the alloy was subjected to a solution heat treatment for which the mechanical properties were stabilized during room-temperature aging.T6 denotes AA6061 alloys that are solution heattreated and artificially aged.These products are not

Process parameters Unit
Range ----------------------------------------------------------------------------------------- cold worked after the solution heat treatment (ASM Handbook, 1990).The mechanical and chemical compositions of each alloy are presented in Table 1.Aluminum alloys as 300×150×6.25mm, respectively plates are used to fabricate the butt joint.The tool rotates perpendicular to the longitudinal surface of the plate.When the tool rotation and translation of the plate movement occur in the same direction, the plate position is referred as the retreating side.When the rotation and translation are opposed, the plate position is referred as the advancing side.When the rotation and translation are opposed, the plate position is referred as the advancing side.Since, the weld nugget predominantly occupies the retreating side metal (Lee et al., 2003).Therefore, a high strength aluminum alloy (AA2024-T3) is placed on the retreating side, while a low strength aluminum alloy (AA6061-T6) is placed on the advancing side of the FS weld joint.Based on a thorough literature investigation, the parameters used in the present study, such as the tool rotational speed (N), welding speed (F), axial force (P) and pin profiles, are selected (Biswas et al., 2012;Kalaiselvan and Murugan, 2013;Jayaraman and Balasubramanian, 2013).Three major pin profiles are assessed in the present study: Taper (TA), Square (SQ) and Straight Cylinder (SC).SKD -61 tool steel is used to fabricate the rotating tools.This metal is a chromiummolybdenum hot-worked air-hardening steel and therefore has good wear resistance, elevatedtemperature strength and thermal fatigue resistance (Lomolino et al., 2005).The fabricated FSW tools are shown in Fig. 2. The process parameters and their values are presented in Table 2.The fabricated weld samples are kept for further mechanical and metallurgical characterization.The test pieces were prepared from the welded samples to estimate the joint strength and undertake metallographic examinations.The tensile specimens were cut perpendicular to their rolled direction.The test was conducted as per the American Standard for Testing of Materials (ASTM) standard IX reference; the dimensions and fracture samples are in presented in Fig. 3.The design matrix, including the recorded experimental values for the ultimate tensile strength and tensile elongation, is  presented in Table 3.The fractured test pieces were subjected to scanning electron microscopic examination to identify the mode of fracture.The observed SEM Images are presented in Fig. 4. A ductile mode of fracture was identified on the fractured zone if the test pieces were fabricated using the rotating tool equipped with a square pin.Some defective test pieces are magnified to identify the type of defect on the weld  on AA 6061 aluminum alloys against the base material strength.

METHODOLOGY
Response Surface Methodology (RSM): Researchers always look the feasible solution for the optimum boundary region.The optimum values may be either maximum or minimum of a particular function that depends upon the input process parameters.The graphical presentation of proposed methodology which is employed based on response surface methodology using desirability approach is presented in Fig. 6.
Response Surface Methodology (RSM) is a combination mathematical and statistical technique for analyzing the complex problems in which several independent variables influence a dependant variable or the goal is to optimize the response (Montgomery, 1980).In many situations in industries, the independent factors can be written as in quantitative form as in Eq. ( 1).Then these independent factors can be thought of having a functional relationship as follows: Between the response Y and quantitative factors of a 1 , a 2 , a 3 …a n , the function 'Φ' is called response surface or response function.A response surface can be responded to the given set of independent factors.When the 'Φ' is unknown, it can be approximated satisfactorily by polynomial within the experimental region.In the present investigation, RSM is applied to formulate the mathematical model in the form of the multiple regression equation for the quality characteristics of tool pin profile on friction stir welded AA2024-AA6061 aluminum alloys.In this method, the independent variables are viewed as a surface to which a mathematical model is fitted.
The Ultimate Tensile Strength (UTS) and Tensile Elongation (TE) of dissimilar weld joints composed of AA6061-AA2024 aluminum alloys are related to the rotational speed (N), the welding speed (F), axial load (P) and Pin Shape (PS).The surface is represented by the following: A second-order polynomial regression equation is used to represent the response surface 'Y' for K factors: where, β o is the average response, β i , β ii , β ij is the coefficients that depend on the major and interaction effects of the parameters and∈ is the statistical error.A second-order model is useful when approximating the true response surface in a relatively small region near the center point of response surface.This area exhibits a substantial curvature in the true response function 'f'; this function is very flexible, allowing it to take various functional forms by approximating the true response surface.Estimating the β values in the second-order model using the least squares method is easy; in addition, numerous reports indicate that the secondorder model will work well for real-time engineering problems (Design Expert, 2005).The values of the polynomial coefficients are calculated using the Design   ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- (5) The predicted values for the ultimate tensile strength, tensile elongation and their deviations are presented in Table 4.The developed model is verified using the results of an Analysis of Variance (ANOVA) at a 95% confidence level.The results of the ANOVA are presented in Table 5.The higher level of the 'R-Sq' and lower Predicted R-Squared' and Adj.R-Squared' values reveal the adequacy of the model.Therefore, the obtained 'R-Sq' and 'Predicted R-Squared' values agree with the 'Adj.R-Squared' values, thereby confirming the adequacy of the present model.The results of the ANOVA indicate that the selected process parameters are significant factors that affect the ultimate tensile strength and tensile elongation.Using a scatter diagram, the adequacy of the model is validated further.The scatter diagram of the normal plot of the predicted versus actual values for the ultimate tensile strength and tensile elongation is shown in Fig. 7a and  b.The similar values of the predicted and actual values are fitted on a 45º scatter line, thus further validating the present model.In addition, the predicted values are within ±10% error; therefore, the obtained model fits the experiment.

Desirability approach:
The optimum points did not coincide in all cases when the process has multi responses.In such conditions, several statistical methods used for solving multi response problems such as overlaying the contour plot for each response, constrained optimization problems and the desirability approach (Zhang et al., 2005).The multi response optimization process is balancing the responses when the number of responses is two or more than two.The main objective of this research is to maintain the balance between the productivity and product quality.In this study, the productivity factors are rotational speed, welding speed, axial load and pin shapes.Similarly, the quality factors are the ultimate tensile strength and tensile elongation of the fabricated joints.An appropriate selection of productivity factors will achieve the high production rate.Therefore, the productivity factors are playing a vital role in the mass production industries.Quality factors deals in this study are ultimate tensile strength and tensile elongation.Since these factors are very much useful for the precision industries such as aerospace, ship building etc.But these factors are opposite in nature.If rotational speed and axial load is increased, then ultimate tensile strength is increased rather tensile elongation of the welded joint is reduced.Therefore, for these kinds of diversified responses, Derringer and Suich (1980) demonstrated a technique called desirability.It is very useful technique for the research and mass production industries where the productivity and quality factors have high conflict between one another: This approach uses an objective function, D (X), called desirability function and converted into a scale free value (d n ) called individual desirability; m is the number of responses.The desirable ranges are from 0 to 1.0 indicated one or more responses are outside their acceptable limits and 1 indicates the response is in the ideal case.

RESULTS AND DISCUSSION
Using the regression models, the effects of each parameter on the ultimate tensile strength and tensile elongation are visualized using the response surface plot from 5a and b to 7a and b.
Identifying a suitable rotating pin profile for generating a sound weld via a frictional heat and hydrostatic pressure is important; specifically, this pin profile must thoroughly blend dissimilar materials along the weld line.In the surface plots, the ultimate tensile strength of the fabricated weld joints is lower than that of the base metals, regardless of the process parameters.In addition, when the process parameters induce low frictional heat and high material flow, the fabricated welded joints exhibit a lower tensile strength.
The tensile elongation decreases when increasing the rotational speed and axial load; this value increases when increasing the welding speed.The strengthening precipitates cluster toward the Thermo-Mechanically Affected Zone (TMAZ), Heat-Affected Zone (HAZ) and Weld Nugget (WN), demonstrating material flow on the TMAZ and WN; therefore, lower tensile strength is observed on the fabricated joints that are composed of dissimilar aluminum alloys (AA6061-AA2024) (Kalaiselvan and Murugan, 2013).Figure 8a and b show the perturbation plot of the ultimate tensile strength and tensile elongation.This perturbation plot compares the effect of every factor at a particular point in design space (Design Expert, 2005).The possible situations that affect the tensile strength and elongation are discussed below.

Effect of pin shapes:
For the dissimilar aluminum alloys (AA2024-AA6061), utilizing a square pin profile imparts higher tensile strength and tensile elongation than to the tapered and cylindrical pin profiles.The rotating tool pin with flat faces produces large pulsating effects, increasing the ultimate tensile strength (Elangovan et al., 2008).Therefore, the rotating tools equipped with square pins impart high ultimate tensile strength, while the cylindrical and taper pins impart low tensile strength.A similar behavior was observed in all of the experiments.Figure 9a and b to 11a and b show graphical representations of the effects of the process parameters for each pin profile using surface plots.The surface plots are three-dimensional representations of the response to the selected factors (Design Expert, 2005).Therefore, each pin shape and process parameter were plotted to demonstrate its behavior regarding the ultimate tensile strength and tensile elongation.

Effects of tool rotational speed:
Increasing the rotational speed of the tool increases the tensile strength of the joints.Figure 9a shows a response surface graph that reveals the effects of the rotational speed of the tool for each pin profile.The surface plot forms a mound shape or a simple maximum surface (Robert et al., 2003).For the simple maximum type, the response values increase gradually from the stationary edge.Similarly, the tensile strength is increased when the rotational speed gradually increases to the stationary edge (center of surface plot).The lower rotational speed (1500 rpm) generates poor material flow, thereby imparting low tensile strength and coarsening the strengthening precipitates.Re-precipitation, a lowered dislocation density and solubilization at the weld zone decreases the tensile strength of fabricated joints when at the maximal rotational speed (1900 rpm), thus producing surface defects and micro voids (Robert et al., 2003;Li et al., 2012;Hui-Jie et al., 2013).These Figure 9b shows a three-dimensional representation of the rotational speed (N) and pin shapes vs. tensile elongation.A rising ridge (Design Expert, 2005) surface plot is generated from the experimental results.The tensile elongation decreases when increasing the rotational speed.Therefore, the rotational speed encourages the clustering among the strengthening precipitates due to the plastic flow in the weld nugget, the thermo mechanical affected zone and the heat affected zone, regardless of the pin shape (Flores et al., 1998;Murr et al., 1998;Su et al., 2003;Sato et al., 2003;Srivatsan et al., 2007;Sanjay et al., 2012).Therefore, an increase in the rotational speed decreases the tensile elongation of the dissimilar aluminum alloys (AA 6061 and AA 2024) in welded joints.The tool equipped with the square pin exhibits the highest tensile elongation; the second-highest tensile elongation was observed with the tapered pin.

Effects of the welding speed:
The effects of the welding speed for dissimilar aluminum alloys (AA 6061-AA 2024) joined by friction stir welding are shown in response Fig. 9a, which shows the effects of the welding speed vs. the pin shape.The obtained surface plot is a 'mound shape or simple maximum' (Design Expert, 2005).The tensile strength is increased when the welding speed increases to 60 mm/min.Then, the tensile strength decreases when gradually increasing the welding speed to 90 mm/min, regardless of the tool pin shape, due to the increased frictional heat and insufficient heat generation at lower and higher welding speeds (Kumar and Kailas, 2008).The welding speed at the lowest levels (30 mm/min) causes metallurgical transformations that result in poor joint strength.This behavior contributes to the tunneling defects, even at a higher welding speed and pin holes at lower welding speeds (Sato et al., 2003).
The response graphs for the rotational speed (N) and pin shape vs. tensile elongation are shown in Fig. 10b.The obtained surface plot is a 'rising ridge' type (Design Expert, 2005).Increasing the welding speed increases the tensile elongation.The welding speed discourages clustering among the strengthening precipitates, regardless of the tool pin shape (Flores et al., 1998;Murr et al., 1998;Su et al., 2003;Sato et al., 2003;Srivatsan et al., 2007;Sanjay et al., 2012).The pin shapes (e.g., taper, square, cylinder) enhance the material flow, thereby generating localized strain.Therefore, an increase in the welding speed increases the tensile elongation of the friction stir welded AA 6061 and AA 2024 aluminum alloys, regardless of the tool pin shape.

Effects of axial load:
A three-dimensional response surface plot 10 (a) represents the effect of the axial load and pin shapes vs. ultimate tensile strength.The obtained shape of the surface plot is a 'simple maximum' (Design Expert, 2005).The increased axial load increases the joint strength of the specimen to an axial force of 6 kN.Beyond that point, the joint strength gradually decreases when increasing the axial load (Flores et al., 1998;Zhang et al., 2005;Kumar and Kailas, 2008).The higher axial force allowed the tool to plunge into the work piece easily, thereby increasing the plunge depth and generating additional frictional heat.In addition, the higher plunge depth encourages clustering among the strengthening particles and the material flow, imparting adequate joint strength on the fabricated weld joints, regardless of the tool pin profile.Moreover, the lower axial force generates insufficient heat levels because the axial load is directly responsible for the frictional heat generation; this situation results in poor material flow, while a higher axial load produces an excessive material flow along the weld line, increasing the size of the weld nugget (Zhang et al., 2005;Kumar and Kailas, 2008).Similar behavior was observed with the tools equipped with tapered and cylinder pin profiles.
Figure 11b presents the three-dimensional surface plot describing the effects of axial load and pin shapes vs. tensile elongation.The obtained surface plot is a  'rising ridge' type.The axial load is vital for the frictional heat generation and the plunging depth of the tool pin profile (Flores et al., 1998;Zhang et al., 2005;Kumar and Kailas, 2008).Therefore, increasing the axial load encourages clustering among the strengthening precipitates, thus reducing the tensile elongation on the weld joints between AA 6061 and AA 2024 aluminum alloys, regardless of the pin shapes.
Multi response optimization of process parameters through desirability: Composite desirability is the weighted geometric mean of the individual desirability for the responses.The factor settings with maximum total desirability are considered to be the optimal parameter conditions.The simultaneous objective function is a geometric mean of all transformed responses (Derringer and Suich, 1980;Zhang et al., 2005).This combination has been evaluated with the help of the Design Expert Software.Two responses such as ultimate tensile strength, tensile elongation have been used to optimize simultaneously using developed mathematical model Eq. ( 4) and ( 5) based on desirability function.In a multi response domain, a measure of how the solution has satisfied the combined goals for all responses must be assured.The optimality solution is to evaluate the input process parameters in experiment range for maximizing ultimate tensile strength and tensile elongation of the fabricated welded joints.The input parameter their ranges, goals and predicted desirable values of responses under prescribed conditions presented in Table 6 and 7 and its graphical representation of contour plot is presented in Fig. 12.
Once the optimal process input parameters are selected then the final step is to predict and verify the improvement of the performance characteristic using the optimal level of the friction stir welding parameters.Then the confirmation of experiments was conducted in order to verify the predicted friction stir welding parameters of the optimal parametric setting for ultimate tensile strength and tensile elongation.Table 8 show the percentage of error of the developed models for the responses with optimal parameter setting during FS welding process.In Table 8, it can be observed that the calculated error is small.Obviously, this confirms excellent reproducibility of the experimental conclusions.

CONCLUSION
Based on the present study, the following theoretical and experimental conclusions can be drawn: • The mathematical models were developed at 95% confidence level for the desired parameters such as rotational speed (N), welding speed (F), axial load (P) by varying the pin shapes.
• The ultimate tensile strength of the fabricated welded joints is lower than the base materials (AA 6061 and AA 2024 aluminum alloys).• The increased rotational speed (N) and axial load (P) parameters decrease the tensile elongation, while the tensile elongation increases after increasing the welding speed (F), regardless of the pin shape.• The increased axial load increases the friction heat generation and the plunging of the tool pin, promoting clustering among the strengthening precipitates.Therefore, higher tensile strengths were obtained using the fabricated weld joints.Therefore, the present investigation findings along with various mathematical models will provide effective guideline to select parameter settings for achieving desired ultimate tensile strength and tensile elongation during friction stir welding of aluminum alloys of AA 2024 and AA 6061.

Fig. 1 :
Fig. 1: FSW machine setup and position of aluminum alloys

Fig. 6 :
Fig. 6: Graphical demonstration of present RSM coupled with desirability approach

Table 1 :
Chemical composition and mechanical properties of AA2024 and AA6061 aluminum alloy

Table 2 :
Process parameters and their range

Table 3 :
Design matrix with their experimental values of Ultimate Tensile Strength (UTS), Tensile Elongation (TE) Exp No.

Table 4 :
Expert version 8 statistical software.Therefore, the regression coefficients of the second-order polynomial equation are obtained.The coded equations are presented in Eq. (4) and (5): Experimental vs. predicted values of Ultimate Tensile Strength (UTS), Tensile Elongation (TE)

Table 6 :
Predicted vs. observed optimum values of responses through desirability

Table 8 :
Predicted vs. observed optimum values of responses through desirability Fig. 12: Contour plot of overall desirability function • The conformability of the predicted results indicate that the mathematical model and the application of the RSM technique are sufficient when studying the friction stir welding process with AA 6061 and AA 2024 aluminum alloys.• The rotating tools equipped with square pins are vital in this study during frictional heat generation; this pin profile is influential during the development of tensile strength in weld joints fabricated from AA 6061 and AA 2024 aluminum alloys.