### 1. Introduction

### 2. Experimental Methods

### 2.1 Materials

### 2.2 Friction Stir welding

### 2.3 Selection of parameters and levels

### 2.4 Orthogonal array experiment

### 2.5 Tensile Testing

### 3. Results and Discussion

### 3.1 Tensile Test Results of Taguchi Matrix

### 3.2 Signal to Noise Ratio (S/N)

##### Table 7

Experiment No. | Ultimate tensile strength, MPa | S/N ratio | ||||||
---|---|---|---|---|---|---|---|---|

1 | 337 | 50.58 | ||||||

2 | 332 | 50.77 | ||||||

3 | 338 | 50.32 | ||||||

4 | 382 | 51.68 | ||||||

5 | 399 | 52.01 | ||||||

6 | 383 | 51.45 | ||||||

7 | 394 | 51.94 | ||||||

8 | 408 | 52.19 | ||||||

9 | 411 | 52.27 |

_{i}’ is the observed result (response) of each experiment. The calculated S/N ratio values (mean) as per equation (1) are given in Table 8 and graphically presented in Fig. 2. The maximum effectiveness ranks were calculated on the basis of delta values which represent the variance (scatter) between the highest and lowest average response values for each factor.

##### Table 8

### 3.3 Interaction Plots for response analysis

### 3.4 Estimation of optimum parameters

_{I}), ‘Linear travel speed’ of 400 mm/min (B

_{II}) and ‘Tilt angle’ of 2° (C

_{II}). However, interaction contour plots show that the maximum properties can also be achieved at ‘Tool rotation speed’ of 960 to 1000 rpm and ‘Linear travel speed’ of 400 to 600 mm/min also.

### 3.5 Prediction of optimum parameters by Regres- sion Equation

### 3.6 Prediction of optimum parameters by Theoretical and Numerical modeling

_{m}(℃) are maximum and melting temperature, respectively, ω is ‘Tool rotation speed’, ν is ‘Linear travel speed’ and K and α are constants (taken as 0.7 and 0.05 respectively). The results obtained for maximum temperature are reported in Table 10. The results show that for combination 1000/600/2, maximum temperature attained has the minimum value.

##### Table 10

FSW Process parameters | Max. Temp. (°C) | |||
---|---|---|---|---|

Tool rotation speed, (rpm) | Linear travel speed, (mm/min) | Tilt angle, (°) | Theoretical | Simulated |

1000 | 400 | 2 | 579 | 626 |

1000 | 500 | 2 | 573 | 617 |

1000 | 600 | 2 | 568 | 608 |

### 3.7 Selection of optimum parameters

### 3.8 Validation Test

### 3.9 Analysis of Variance (ANOVA)

^{2}. This coefficient is a statistical number which shows how much the data is fitted to the regression line. The measured value of R

^{2}is 97.46% as shown in Table 10. As this value is almost equal to one, it can be concluded that the developed model has high accuracy8,22).

##### Table 11

### 4. Conclusions

1) Taguchi Design of Experiment technique can be efficiently used to optimize the process parameters of friction stir welding process of thin sheets of aluminum.

2) S/N analysis showed that the maximum tensile strength can be attained when values of ‘Tool rotation speed’, ‘Linear travel speed’ and ‘Tilt angle’ were 1000 rpm, 400 mm/min and 2°, respectively. The attainable UTS was 409 MPa.

3) Since heat generated during FSW has great influence on the tensile strength of the joint, Interaction Contour plots and regression analysis were used to refine the optimum parameters. The results showed that the same tensile strength can be achieved by utilizing a higher ‘Linear travel speed’ of 600 mm/min.

4) The theoretical analysis and FE modeling showed that welding at higher ‘Linear travel speed’ can offer same results at lower peak temperature.

5) A maximum tensile strength of 412 MPa was achieved by the FSW joint made by the optimized parameters of 1000 rpm ‘Tool rotation speed’, 600 mm/min ‘Linear travel speed’ and 2° ‘Tilt angle’.

6) ANOVA analysis demonstrated that ‘Tool rotation speed’ has the most significant effect on the tensile strength of the joint with 92.3% contribution followed by ‘Linear travel speed’ and ‘Tilt angle’ having 4% and 1.16% contribution respectively.