# Parameters Optimization of Dissimilar Friction Stir Welding for AA7079 and AA8050 through RSM

Authors: M. Kavitha; V. M. Manickavasagam; T. Sathish; Bhiksha Gugulothu; A. Sathish Kumar; Sivakumar Karthikeyan; Ram Subbiah
Journal: Advances in Materials Science and Engineering
 (2021)

---

## Abstract

Aluminium alloy is widely used in engineering application, and it can be classified based on the constituent elements or alloying elements. Aluminium alloy is preferred for the nature of its tensile strength, ductility, and corrosion resistance in this research to make a dissimilar friction stir welding joint of aluminium alloys 7079 and 8050 materials. The tensile strength of the weld joint is estimated by the influence of the response surface methodology approach. The welding is carried out by preferred process parameters with a tool speed of 1000–2500 rpm, tool pin diameter of 2–6 mm, welding speed of 50–300 mm/min, and tool shoulder diameter of 10–20 mm. The ANOVA analysis and the prediction of tensile strength were conducted efficiently. From the RSM analysis, the tool pin diameter mostly modified the output of the result.


---

## Body

## 1. Introduction

The novel technique joins the material permanently by using the friction stir welding process, and the nonconsumable tool is applied to carry the welding process. One best advantage of the FSW process is, without melting the work samples during welding, heat is introduced between tool rotation and specimens [1–3]. The welding is carried out along the straight line in a longitudinal manner of tool movement to join the samples. The homogeneous mixture is achieved applying the pressure in the joint area (soft region) of the specimens. The FSW process effectively joins all alloys such as aluminium alloys, titanium alloys, copper alloys, magnesium alloys, and steel material by a similar or dissimilar mode. This welding is now fruitfully used in joining polymers, and the FSW process is carried out by Wayne Thomas at TWI Ltd. in 1991 [4–6]. Most of the aluminium alloy is used in the ship building, automotive segment, and aerospace sectors. The different tool profiles are used in friction stir welding as cylindrical, square triangular, and threaded, and the tool rotates and passes through a straight line mode [7]. The shoulder diameter is big in size compared to tool pin diameter, and the pin of the tool plunges into work pieces effectively [8]. The pin rotates at high speed with intercombination of materials carried out efficiently. The microstructure changed by means of stirring action; it causes the swap of particles from one material to another one remarkably. The strength of the joint is increased, and to form a rigid structure, the study of different zones in the welded area is very important in the friction stir welding process. In arc welding, gas welding and other types of the welding process formed lot of defects, but this FSW process eliminates or minimizes the welding defects if using any material with various parameters [9]. The FSW process is mainly used to make butt joint, eventhough lap joints are also carried in the FSW process. For the past research, the dissimilar friction stir welding of AA7079 and AA8050 is through response surface methodology. The influence of different process parameters is to evaluate the tensile strength of the weld joint successfully. RSM is a statistical technique to find the optimal parameters and the maximum range of the output value [10–12].


## 2. Materials

The friction stir welding process planned to make dissimilar aluminium alloy materials such as AA7079 and AA8050. The chemical composition of both the materials is tabulated with their weight percentage in Table1.Table 1
Chemical composition of AA7079 and AA8050.
Material% of composition of AA7079% of composition of AA8050Cr0.20.05Cu0.60.05Fe0.21.2Mg3.50.05Mn0.250.85Si0.250.03Zn4.00.1Ti0.7—AlRemainingRemainingThe aluminium alloy 7079 has a wrought alloy with a heat treatable mode, and it has extraordinary strength. It possesses good machinability and workability characters; this alloy is mainly used in the high stressed parts. In the air wings parts, this alloy played a major role in hydraulic function units. The AA8050 aluminium alloy has good strength easy to modify any shape; it has high corrosion resistance behaviour. This alloy can be used in the body building industries.


## 3. Experimental Procedure

The FSW process considers the process parameters, and all the factors and their values are given in Table2.Table 2
FSW factors and its values.
NotationFactorsLowHighATool speed (rpm)10002500BTool pin diameter (mm)26CWelding speed (mm/min)50300DShoulder diameter (mm)1020The factors are tool speed (1000–2500 rpm), tool pin diameter (2–6 mm), welding speed (50–300), and shoulder diameter (10–20). The friction stir welding process specimens prepared under the dimensions are 100∗50∗5 mm for each plate [13]. The straight cylindrical profile tool and the material of HSS tool is used to weld the specimen effectively (Figure 1). The CNC vertical milling machine was used to weld the samples under the various parameters [14]. The specimens are rigidly fixed on the fixture with the proper clamp, the tool rotated above the top surface of the specimens, and the axial force is applied to the tool. The tool rotated clockwise direction, moved, and penetrated the samples in longitudinal direction, and the weld joint was produced accurately. The tensile test was conducted by the influence of UTM machine.Figure 1
FSW cylindrical tool.


## 4. Result and Discussion

The code value of the experiment, the process factors contribution, and the result of the tensile strength are given in Table3.Table 3
FSW factors contribution and the result of tensile strength.
Experiment no.ABCDTool speed (rpm)Tool pin diameter (mm)Welding speed (mm/min)Shoulder diameter (mm)Tensile strength (MPa)1000017504175151622100−125004175101503100125004175201904010−117506175109250−10117502175201106110025006175151967−10−1010004501520880−1−101750250157990−110175023001512510−1001100041752018411−110010006175151241210−10250045015157130011175043002021214−1−1001000217515130151−1002500217515901601011750617520186170−10−11750217510851800−1−117504501017619−101010004300151462000001750417515852100−1117504502019222000017504175151562301−1017506501513724011017506300158225101025004300159726001−1175043001021127−100−11000417510173In Table4, the ANOVA linear model produced the major contribution of tool pin diameter as 6.38% [15]. In the square model, the tool pin diameter∗tool pin diameter has contributed at 26.33%, and in the 2-way interaction model, the tool speed (rpm)∗tool pin diameter (mm) has the higher percentage contribution such as 6.13%Table 4
Analysis of variance summary.
SourceDFFSeq SSContribution (%)Adj SSAdj MSF valueP valueModel1434385.467.1934385.42456.101.760.167Linear47264.514.197264.51816.121.300.325Tool speed (rpm)1602.11.18602.1602.080.430.524Tool pin diameter (mm)13267.06.383267.03267.002.330.152Welding speed (mm/min)1481.30.94481.3481.330.340.568Shoulder diameter (mm)12914.15.692914.12914.082.080.175Square419976.939.0319976.94994.233.570.039Tool speed (rpm)∗tool speed (rpm)1385.62.711415.61415.561.010.334Tool pin diameter (mm)∗tool pin diameter (mm)13475.026.336471.36471.264.620.053Welding speed (mm/min)∗welding speed (mm/min)159.60.12960.0960.040.690.424Shoulder diameter (mm)∗shoulder diameter (mm)15056.79.885056.75056.683.610.0822-way interaction67144.013.967144.01190.670.850.556Tool speed (rpm)∗tool pin diameter (mm)3136.06.133136.03136.002.240.160Tool speed (rpm)∗welding speed (mm/min)11.00.001.01.000.000.979Tool speed (rpm)∗shoulder diameter (mm)1210.20.41210.3210.250.150.705Tool pin diameter (mm)∗welding speed (mm/min)12550.24.982550.22550.251.820.202Tool pin diameter (mm)∗shoulder diameter (mm)11190.22.331190.31190.250.850.375Welding speed (mm/min)∗shoulder diameter (mm156.20.1156.256.250.040.844Error1216793.832.8116793.81399.48Lack of fit1013125.125.6513125.11312.510.720.708Pure error23668.77.173668.71834.33Total2651179.2100.00Figure2 shows the maximum tensile strength 212 MPa obtained by the influence of tool speed of 1750 rpm, tool pin diameter of 4 mm, welding speed of 300 mm, and shoulder diameter of 20 mm.Figure 2
Number of specimens vs. tensile strength.


## 5. Prediction for Tensile Strength (MPa)

The regression equation in uncoded units is given as follows. Tensile strength (MPa) = 533 – 0.215 tool speed (rpm) + 37.1 tool pin diameter (mm) + 0.133 welding speed (mm/min) − 43.1 shoulder diameter (mm) + 0.000029 tool speed (rpm)∗tool speed (rpm) − 8.71 tool pin diameter (mm)∗tool pin diameter (mm) + 0.00086 welding speed (mm/min)∗welding speed (mm/min) + 1.232 shoulder diameter (mm)∗shoulder diameter (mm) + 0.0187 tool speed (rpm)∗tool pin diameter (mm) + 0.000005 tool speed (rpm)∗welding speed (mm/min) + 0.00193 tool speed (rpm)∗shoulder diameter (mm) − 0.1010 tool pin diameter (mm)∗welding speed (mm/min) + 1.72 tool pin diameter (mm)∗shoulder diameter (mm) − 0.0060 welding speed (mm/min)∗shoulder diameter (mm).


## 6. Solution

Tables5 and 6 illustrate the response optimization parameters and values setting and response optimization of tensile strength, respectively, and there are four factors involved for this experiment. Table 7 presents the prediction for tensile strength (MPa) and the values.Table 5
Response optimization parameters and values setting.
Response optimizationTensile strength (MPa)ParametersTool speed (1000 rpm)Tool pin diameter (2 mm)Welding speed (50 mm/min)Shoulder diameter (10 mm)GoalTensile strength (MPa) maximumResponse importance tensile strength (MPa)Lower 79Target 212Upper 1Weight 1Table 6
Response optimization.
Tool speed (rpm)Tool pin diameter (mm)Welding speed (mm/min)Shoulder diameter (mm)Tool strength (MPa)10002.34430010211.428Table 7
Prediction for tensile strength (MPa).
Multiple response predictionVariable settingTool speed (rpm)1000 rpmTool pin diameter (mm)2.44440 mmWelding speed (mm/min)300 mm/minShoulder diameter (mm)10 mmResponseFitSE fit95% CI95% PITensile strength (MPa)211.451.1(100.0, 322.9)(73.4, 349.5)The numerical response optimizer used to create an optimal set of factors involving to offer the maximum tensile strength is shown in Figure3. In this study, the main target of the result is to maximize the tensile strength. From the graph, it involves predicting tensile strength as the optimum factor of tool speed of 1000 rpm, tool pin diameter of 2.4 mm, welding speed of 300 mm/min, and shoulder diameter of 10 mm, offering the maximum tensile strength of 211.48 MPa.Figure 3
Numerical response optimizer graph.Figure4 shows the maximum tensile strength obtained by interaction of pin diameter, the tool speed has fixed as 1700 rpm, the tool pin has 4 mm diameter, and the maximum tensile strength was obtained as 170 MPa. In this experiment, Figure 5 illustrates the maximum tensile strength offered by the welding speed interaction, the tool pin diameter is fixed as 4 mm, welding speed is 175 mm/min, and the maximum tensile strength obtained is 160 MPa. The welding speed graph in Figure 6 shows that the welding speed has fixed as 175 mm/min, the maximum tensile strength produced by shoulder diameter interaction. The shoulder diameter of 15 mm influenced to produce the maximum tensile strength as 138 MPa.Figure 4
Tool speed graph, tool pin diameter vs. tensile strength.Figure 5
Tool pin graph, welding speed vs. tensile strength.Figure 6
Welding speed graph, shoulder diameter vs. tensile strength.


## 7. Conclusion

The dissimilar friction stir welding of AA7079 and AA8050 aluminium alloy jointed efficiently applying straight cylindrical tool. The response surface methodology was implemented to find the maximum tensile strength and the optimal parameters. The output of this experiment is drawn as follows:(1)
From the analysis of variance, in the liner model, the major contribution of tool pin diameter was 6.38%, in the square model, the tool pin diameter∗tool pin diameter has contributed at 26.33%, and in the 2-way interaction model, the tool speed (rpm)∗tool pin diameter (mm) has the higher percentage contribution such as 6.13%(2)
The maximum tensile strength 212 MPa was obtained by the influence of tool speed of 1750 rpm, tool pin diameter of 4 mm, welding speed of 300 mm, and shoulder diameter of 20 mm(3)
For the predicted analysis, the optimum factor of tool speed of 1000 rpm, tool pin diameter of 2.4 mm, welding speed of 300 mm/min, and shoulder diameter of 10 mm offered the maximum tensile strength of 211.48 MPa. The predicted tensile strength and the response optimized tensile strength values are near, since the four factors and the values of this evaluation were good.(4)
Further scope of this study was extended to conduct friction stir processing (FSP) to modify the surface structure of the dissimilar materials



---

*Source: 9723699-2021-07-17.xml*