Microstructure and mechanical properties on friction stir processed TIG welded dissimilar joints of AA5052-H32 and AA5083-H111 alloys by grey approach

1. INTRODUCTION

Nowadays, the firms are in the need of unconventional light-weight materials for production and fabrication with a good thermal and electrical conductivity (Praveen et al., 2005Praveen, P., Yarlagadda, P.K.D.V., Kang, M.J. (2005). Advancements in pulse gas metal arc welding. J. Mater. Process. Technol. 164-165, 1113-1119. https://doi.org/10.1016/j.jmatprotec.2005.02.100.). In this respect, aluminium alloys are superior materials among various types of metals and alloys, and they can be welded together by employing different techniques. The TIG welding process is a good process for the joining of aluminium alloys compared to other joining techniques (Yazdipour et al., 2011Yazdipour, A.R., Shafiei, M., Jamshidi Aval, H. (2011). An investigation of the microstructures and properties of metal inert gas and friction stir welds in aluminium alloy 5083. Sadhana 36, 505-514. https://doi.org/10.1007/s12046-011-0032-6.). The 5XXX aluminium alloys show superplasticity and they are used in various applications such as marine, railways, automotive and aircraft sectors. These alloys possess high corrosion resistant because of the presence of magnesium in its composition and it is also used for fabricating pressure vessels (Pavan et al., 2021Pavan, A.R., Chandrasekar, N., Arivazhagan, B., Kumar, S., Vasudevan, M. (2021). Study of arc characteristics using varying shielding gas and optimization of activated-TIG welding technique for thick AISI 316L(N) plates. CIRP J. Manuf. Sci. Technol. 35, 675-690. https://doi.org/10.1016/j.cirpj.2021.08.013.; Mohan Kumar et al., 2022Mohan Kumar, S., Rajesh Kannan, A., Pramod, R., Siva Shanmugam, N., Dhinakaran, V. (2022). Testing, characterization and numerical prediction (uni-axial tension and bend test) of Double-side TIG welded SS321 plate for pressure vessel application. Int. J. Press. Vessels. Piping. 197 (15), 104648. https://doi.org/10.1016/j.ijpvp.2022.104648.). A high mechanical strength can be achieved by the TIG welding, making it suitable for various applications. The TIG welding process is very suitable for constructions and other mechanical fabrication sectors (Huang et al., 2018Huang, L., Wu, D., Hua, X., Liu, S., Jiang, Z., Li, F., Wang, H., Shi, S. (2018). Effect of the welding direction on the microstructural characterization in fiber laser-GMAW hybrid welding of 5083 aluminum alloy. J. Manuf. Process. 31, 514-522. https://doi.org/10.1016/j.jmapro.2017.12.010.). The mechanical properties of joining materials are mainly affected during TIG welding. The chosen TIG welding process parameters are the filler rod diameter, the shielding gas flow rate and the current. The weld zone properties are mainly influenced by the current. The optimum current exhibits better quality for welding.The other inputs like,the filler rod material, the shielding gas and the number passes influence theformation of residual stress (Pawan et al., 2013Pawan, K., Anoop, C.A., Kumar, S. (2013). Study of Heat Input for GTA Welded Aluminium Alloy 7039. Int. J. Eng. Sci. Innov. Technol. 2 (5), 150-156. https://doi.org/10.13140/RG.2.2.10701.44009.; Senthil kumar et al., 2007Senthil Kumar, T., Balasubramanian, V., Babu, S., Sanavullah,M.Y. (2007). Effect of Pulsed Current GTAW Parameters on Fusion Zone Microstructure of AA6061 aluminium alloy. Met. Mater. Int. 13, 345-351. https://doi.org/10.1007/BF03027892.). The defects that occurred in the welded specimen are mainly due to poor parameters selection. The defects are undercuts, scarce penetration of weld joints and unseemly weld surface. The temperature is the main factor for obtaining good quality welds and it is main influencing factor of the microstructure of the weld (Correa et al., 2009Correa, E.O., Costa, S.C., Santos, J.N. (2009). Studies on weldability of iron-based powder metal alloys using pulsed gas tungsten arc welding process. J. Mater. Process. Technol. 209 (8), 3937-42. https://doi.org/10.1016/j.jmatprotec.2008.09.008.; Ambriz et al., 2010Ambriz, R.R., Barrera, G., García, R., López, V.H. (2010). Effect of the weld thermal cycles of the modified indirect electric arc on the mechanical properties of the AA6061-T6 alloy. Weld. Int. 24, 321-328. https://doi.org/10.1080/09507110903568778.; Rojas et al., 2020Rojas. H., Molina, A., Valdez, S., Campillo, B., Martínez H., Sedano, A., Serna, S. (2020). The impact of heat input on the microstructures, fatigue behaviors, and stress lives of TIG-welded 6061-T6 alloy joints. Mater. Res. Express. 7, 126512. https://doi.org/10.1088/2053-1591/abd136.). Durgutlu (2016)Durgutlu, A. (2016). The effect of continuous and pulsed current on microstructure and mechanical properties in TIG welding of Al-Si alloy sheets. Kovove. Mater. 54 (5), 345-350. https://doi.org/10.4149/km_2016_5_345. studied the TIG welding technique on an aluminium silicon alloy using different process parameters. They performed mechanical tests to investigate the weld strength. The influence of the alternative and pulsed currents was analyzed and the alternative current exhibits maximum strength. Samiuddin et al. (2021)Samiuddin, M., Li, J., Taimoor, M., Nouman Siddiqui, M., Siddiqui, S.U., Xiong, J. (2021). Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization. Def. Technol. 17 (4), 1234-1248. https://doi.org/10.1016/j.dt.2020.06.012. investigated the TIG welded 5083 alloy to analyze the microstructure and the mechanical performance for cryogenic applications. Most of the mechanical properties showed defect free joints. Gulshan and Ahsan (2014)Gulshan, F., Ahsan, Q. (2014). Effect of Heat Input on the Structure and Properties of Aluminium Weldment TIG Welded with 4043 Filler Rod. Chem. Mater. Eng. 2 (2), 25-32. https://doi.org/10.13189/cme.2014.020201. analysed the TIG welding input parameters of aluminium alloy 1XXX for mechanical properties. In this investigation, the bonding structure and mechanical properties were analysed by utilizing the proper equipment. It was found that higher values of the heat input parameter led to better mechanical properties. Chawinee et al. (2010)Chawinee, P., Pusit, M., Tapany, U., Rattana, B. (2010). Effects of Aluminium Alloy Surface Preparation in TIG Dissimilar Metals Welding between Mild Steel and 5052 Aluminium Alloy. Proceed. 12th. Int. Conf. Aluminium. Alloys, Japan, pp. 961-965. investigated the quality of the modified surface after using the TIG welding method to join a mild steel and 5052 aluminium alloy. The inclusion and non-inclusion of oxide layers was analysed. The presence of the oxide layer produced better quality surfaces. Chanakyan et al. (2020)Chanakyan, C., Sivasankar, S., Meignanamoorthy, M., Ravichandran, M., Alagarsamy, S.V., Dinesh Kumar, S., Sakthivelu, S. (2020). Friction stir processing (FSP) of numerical study based on design of experiment-review. Mater. Today. Proceed. 27 (2), 748-751. https://doi.org/10.1016/j.matpr.2019.12.035. used three tool pin to predict the optimum process parameters of Friction Stir processing while joining 5052 aluminium alloys with each other. The optimum process parameters exhibited superior mechanical properties. Elmariung et al. (2021)Elmariung, A., Sivagami, S.M., Chanakyan, C., Arockiam, J., Sathishkumar, G.B., Meignanamoorthy, M., Ravichandran, M., Alagarsamy, S.V. (2021). Mechanical properties on INCONEL 800H alloy by TIG welding process. Mater. Today. Proceed. In Press https://doi.org/10.1016/j.matpr.2021.01.049. analysed the TIG welding of an Inconel alloy by considering the voltage, the current and the speed parameters. The selected parameters exhibit the best mechanical properties with minor defects and this was confirmed by the microstructural study.

Chanakyan et al. (2021b)Chanakyan, C., Sivasankar, S., Meignanamoorthy, M., Alagarsamy, S.V. (2021b). Parametric Optimization of Mechanical Properties via FSW on AA5052 Using Taguchi Based Grey Relational Analysis. Incas. Bulletin 13 (2), 21-30. https://doi.org/10.13111/2066-8201.2021.13.2.3. optimized the FSP parameters with the Taguchi approach and the ANOVA method. This approach is found useful to select the best parameters to get optimum mechanical properties. Jagathesh et al. (2017)Jagathesh, K., Jenarthanan, M.P., Dinesh Babu, P., Chanakyan, C. (2017). Analysis of factors influencing tensile strength in dissimilar welds of AA2024 and AA6061 produced by Friction Stir Welding (FSW). Aust. J. Mech. Eng. 15 (1), 19-26. https://doi.org/10.1080/14484846.2015.1093229. analyzed the tensile properties of FSW aluminium alloy 2024 and aluminium alloy 6061 using various input factors like the spinning speed, the diameter of tool pin and the traverse speed. The optimized parameters are determined by using the Taguchi based response surface methodology. Chanakyan and Sivasankar (2020)Chanakyan, C., Sivasankar, S. (2020). Parametric studies in friction stir welding on Al-Mg alloy with (HCHCr) tool by Taguchi based desirability function analysis (DFA). J. Ceram. Process. Res. 21 (6), 647-655. https://doi.org/10.36410/jcpr.2020.21.6.647. also studied a numerical based analysis on various investigations. These studies found this approach as a very capable analysis method to obtain better optimum process parameters of FSP related studies. The FSP is a solid state joining technique that aims to obtain joints with optimum mechanical properties.

In this study, the process parameters of the TIG welding are optimized by using various techniques and the mechanical characteristics of the TIG welded joints are analysed. Besides, the input parameters of the FSW process are also optimized by using various techniques and the mechanical properties of the resulting FSP welded microstructures are also analysed. In the literature, there is no previous attempt made on the optimization of FSP parameters of TIG butt welded AA5053-H32 and AA5083 - H111 aluminium alloy with regards to the UTS, Vickers hardness and % of elongation. In this research, the TIG welding of AA5052-H32 with AA5083 - H111 alloy is carried out. The input parameters of the FSP on TIG welded bead of aluminium alloy 5052-H32 and aluminium alloy 5083 - H111 are optimized to obtain the optimum UTS, Vickers hardness and % of elongation.

2. EXPERIMENTATION

2.2. Fabrication method

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The AA5052-H32 and AA5083-H111 alloys were used with dimensions of 150×55×5 mm. Each welding specimen was notched to 45° by using the Wire cut EDM. The specimens were cleaned by using silica sheets and alumina paste before welding. The Miller - Syncrowave power source were employed for TIG welding of AA5052-H32 and AA5083-H111 alloys. The ER5356 filler rod, a current of 170 amps, a shielding gas flow rate of 11 l·min^-1 and a diameter of filler rod of 2.4 mm were employed for the TIG welding of the proposed aluminium alloys. The shielding gas selected for this investigation was argon. To enhance the joint efficiency, the application of the secondary process was needed on the TIG welded specimen. The secondary process consisting in using the Friction Stir Processing (FSP) with pin less tool with dimension of 40 mm of shoulder length, with 20 mm diameter of shoulder. In this research, the optimization of the FSP process parameters on the TIG welded AA5052-H32 and AA5083-H111 alloys was done by utilizing the Taguchi based GRA approach. The selected input parameters used in the FSP were the total travel speed, the total rotation speed and the number of passes. The schematic layout of FSP is shown in Fig. 1. The processed specimen is exhibited in Fig. 2.

Figure 1.  Configuration of FSP applied on the TIG butt welded joints using a pin less tool.

Figure 2.  Friction stir processed on TIG welded sample.

The factor ranges considered in the selection of The FSP parameters are displayed in Table 1. The L9 OA was chosen for the optimization. Table 2 presents the L9 array with the different input FSP parameters considered for each sample.

Table 1.  Factor ranges considered in the selection of the FSP parameters

Parameters	Abbreviation	Factors
		1	2	3
Tool rotation speed (RPM)	X (TR)	850	950	1050
No of passes	Z (NP)	1	2	3
Tool travel speed (mm/min)	Y(TT)	24	28	32

Table 2.  L9 OA with Friction Stir Processing (FSP) parameters

Sample Nº	Tool rotation speed	Tool Transverse speed	Nº of passes
1	850	24	1
2	850	28	2
3	850	32	3
4	950	24	2
5	950	28	3
6	950	32	1
7	1050	24	3
8	1050	28	1
9	1050	32	2

3. RESULTS AND DISCUSSION

The optimization of the input parameters of FSP on TIG welded AA5052-H111 and AA5083-H32 alloys were done by utilizing the Grey Relational Approach (GRA) approach. The L9 orthogonal arrays input parameters and its responses are mentioned in Table 3. Three trials were carried out for every combination of L9 orthogonal array parameters and the average value of each response parameters has been taken.

The GRA was employed for the computation of the optimal FSP parameters for UTS, Vickers hardness and % of elongation. The following four steps were utilized in the optimization: normalization matrix, finding of Grey Relational Coefficient, finding of Grey Relational grade and finding of rank, for every combination of FSP parameters of the L9 orthogonal array. Table 4 shows the GRA with L9 orthogonal array FSP parameters.

GRA methodology is the best optimization tool for multiple responses and it is also named as multi objective tool for optimization. The normalized matrix, GRC, GRG and ranks were determined for L9 array of FSP parameters of TIG welded dissimilar aluminium alloys. The Trail no.5 exhibits better responses among the L9 trials. The GRG value of L9 combination of parameters was compared with each other and it is shown in Fig. 3. The highest GRG value was obtained from trial no. 5.

The Grey Relational Grade was taken as the response parameter for the optimization of the FSP parameters on TIG welded dissimilar aluminium alloys. The Minitab 19 software was employed for optimization. Table 5 exhibits the response table for the GRG.

The UTS, Vickers hardness and % of elongation are significantly influenced by the number of passes, followed by total rotational speed and total transverse speed. The main interaction effect with their grey S/N ratios is illustrated in Fig. 4.

From the main effect plot, medium level of rotational and transverse speed with maximum level number of passes exhibit better UTS, Vickers hardness and % of elongation. Increasing the rotational speed increases the GRG value upto 950 rpm and then decreases at the 1050 rpm rotational speed. Increasing the transverse speed increases the GRG value upto 28 mm·min^-1 and then decreases for 32 mm·min^-1. Increasing the number of passes decreases the GRG value down to 2 number of possesses and again increases the GRG value after 3 passes. Increasing of number of passes led to fine grain formation. The FSP process leads to fine grain formation on the TIG welded surface. The fine grains enhanced the mechanical properties of FSP processes TIG welded aluminium joints. The fine grain formation also increases the bonding strength between the particles of TIG welded surface. The optimized input process parameters for FSP are A2B2C3. The ANOVA for GRG is shown in Table 6. The ANOVA was utilized to analyse the importance of all input process parameters on the responses Chanakyan et al. (2021a)Chanakyan, C., Sivasankar, S., Meignanamoorthy, M., Ravichandran, M., Mohanavel, V., Saleh, A., Hesham, S.A., Manikandan, V., Ramesh Lalvani, J.I. (2021a). Optimization of FSP Process Parameters on AA5052 Employing the S/N Ratio and ANOVA Method. Adv. Mater. Sci. Eng. 2021, 6450251. https://doi.org/10.1155/2021/6450251.. Besides, ANOVA was applied to compute the contribution percentage of each input process parameter on the GRG.

The ANOVA Table 6 shows the contribution percentage of total rotational speed; total transverse speed and number of passes are 25.8, 19.7 and 54.3%, respectively. The influencing sequences of input process parameter of FSP are the number of passes, total rotational speed and the total transverse speed. Consequently, the contour plots of various combinations of input process parameters for different responses are shown in Fig. 5 (a-c).

The contour plot for the rotational speed and the transverse speed on the GRG reveals that medium level of rotational speed 950 rpm and medium level of transverse speed 28 mm/min exhibit highest the GRG value as it was shown in Fig. 5a. The Fig. 5b depicts the relationship between the transverse speed and number of passes, revealing that the highest number of passes (3) with a medium level of transverse speed enhances the GRG value. Figure 5c shows that the medium level of total rotational speed 950 rpm and 3 passes exhibit higher GRG value among the possible combinations.

The confirmation test was done for the A2B2C3 combination of input process parameters of FSP. The confirmation test specimen was TIG welded at 170 A of current, 2.4 mm diameter of filler rod and 11 l·min^-1 gas flow rate. The filler material ER5356 was employed for the TIG welding. The TIG welded dissimilar alloy sample was further FSP processed at the condition of 950 rpm rotational speed, 28 m·min^-1 transverse speed and using 3 passes. The two trails were done for assessing the UTS, Vickers hardness and % of elongation. The two trails were conducted for the confirmation test process parameters.

The UTS, Vickers hardness and % of elongation obtained were 246 MPa, 112 HV and 19.2%. The joint efficiency of the FSP processed TIG welded AA5052-H32 and AA5083-H111 are enhanced to 102.5%. The confirmation test specimen was displayed in Fig. 6 (a-b).

Scanning Electron Microscopy was employed for analysing the fracture surface of the confirmation test specimen of FSP processed TIG welded AA5052-H32 and AA5083-H111. The result is shown in Fig. 7. Porosities were formed in some places of the confirmation test specimen. Besides, oxides were formed in some regionon the fractured surfaces of the confirmation test specimen. The fractured surface reveals that ductile fracture was occurred.

4. CONCLUSIONS

The TIG welding of aluminium alloy 5052-H32 and aluminium alloy 5083-H111was done at 70 A of current, 11 l·min^-1 of gas flow rate and 2.4 mm of ER5356 filler rod material. The TIG welding dissimilar aluminium alloy sample has a low joint efficiency when compared to base metal joint strength. For this reason, the FSP was employed on the surface of the TIG welded sample. The implementation of the FSP process on the TIG welded samples was successfull, decreasing the grain size. The optimization of FSP process parameters on TIG welded TIG welded joint was done by the Grey Relational Approach (GRA). The input process parameters of the FSP process are the total rotational speed, the total transverse speed and the number of passes. Response parameters are selected for this investigation to enhance the ultimate tensile strength (UTS), Vickers hardness and % of elongation. The optimum combination of input FSP parameters was A2B2C3. The influencing parameter sequence of FSP was the number of passes, the total rotational speed and the transverse speed. Its contribution percentage for the GRG was 54.3, 25.8 and 19.7%, respectively. The microstructure of the TIG welded AA5052-H32 and AA5083-H111weld bead was analysed before and after the implementation of the FSP by using SEM. The SEM image of the fractured surface confirmation test specimen shows that there were no considerable defects and a ductile fracture. The efficiency of joint processed by a combination of FSP and TIG was increased to around 103%.