Characteristics of Mechanical Properties and Microstructure of Micro Friction Stir Spot Welding of AA1100 and Brass

Friction stir spot welding (FSSW) is a type of solid state welding that has been widely developed using both similar and dissimilar materials. Aluminum AA1100 (99% Al) and brass (Cu-Zn) with a thickness of 0.42 mm are used in this welding joint. This research investigates the characteristics of the lap shear force and microstructure of micro FSSW joints on similar aluminum alloy AA1100, similar brass, and dissimilar AA1100–brass materials using a pin tool made of high-speed steel. The constant process parameters of the micro FSSW joint were plunge depth, dwell time, plunge rate, and high tool rotational speed of 0.7 mm, 6 s, 4 mm/min, and 33,000 rpm, respectively. Micro FSSW joints were carried out on similar AA1100, similar brass, and dissimilar materials whereby AA1100 was the upper sheet and brass was the lower sheet. The results of this research show that micro FSSW joints have a higher lap shear force on similar materials than dissimilar materials. The number of spots on the similar AA100 had no significant effect on the lap shear force, while with similar brass, the number of spots had a significant effect on lap shear force. The formation of a very thin intermetallic compound layer in the nugget zone occurred in the dissimilar materials. Moreover, observation results indicate that the similar AA1100 and similar brass had a lap shear force with a plug fracture type, while the type of fracture found in dissimilar materials was the interface failure mode.

AA1100; Brass; Friction stir spot welding; Lap shear force; Microstructure

    Currently, lightweight materials such as aluminum alloys are often used in the manufacturing and automotive industries. Aluminum AA1100 is among the materials used for the manufacture of lightweight structures that are commonly used in resistance spot welding (Baskoro et al., 2017; Hakam et al., 2018), friction stir spot welding (FSSW), and conventional welding techniques such as gas tungsten arc welding. Micro FSSW is a derivative of friction stir welding, in that mFSSW uses materials with a thickness of less than 1000 µm, as was first discovered by TWI 1991. Micro FSSW is a solid-state joining process whereby the heat generated comes from the rotation of the tool and workpiece, and it can be used as an alternative to rivet joints. The temperature generated from this solid-state process is below the melting temperature of the base metal, so it can reduce defects that usually occur in conventional welding, namely porosity, distortion, residual stress, and impurity. A micro FSSW joint can be carried out on both similar and dissimilar materials. Several studies of FSSW on similar materials, including that of Lin et al. (2012), have reported that dwell time causes the bonding area to be larger, thus increasing the shear strength of an FSSW welding joint on magnesium. They also mentioned that high rotational speed and dwell time produce a finer microstructure in the stir zone to increase the shear strength of the material. Yazdi et al. (2019) observed that the use of pinless tools might increase the effective bond width area and tensile shear strength micro FSSW of 2 mm thickness AA6061 compared to tools with a pin. Baskoro et al. (2020) reported that dwell time does not affect the maximum temperature, but it does influence the tensile strength of the micro FSSW joint on AA1100 material the most using high-speed rotation.

     An FSSW joint is used for similar materials, but several studies have successfully conducted solid-state joining using FSSW on dissimilar materials. However, welding of dissimilar material FSSW joints can lead to the formation of intermetallic compounds. Bozzi et al. (2010) observed the formation of intermetallic compound (IMC) on AA6016 and galvanized interstitial-free steel materials using tool rotational speed and penetration depth parameters. They reported that when the tool rotational speed and penetration are increased, the thickness of the IMC layer also increases. Esmaeili et al. (2011) examined friction stir welding on dissimilar materials, namely on AA1050 and brass. Li et al. (2014) studied the mechanical properties and how to reduce defects in a micro FSSW joint using a pinless tool on dissimilar AA2024 with a thickness of 1.5 mm using rotating speed and dwell time parameters. They reported that pinless tools reduce the formation of hook defects and increase the tensile shear load. Rao et al. (2015) investigated the effect of FSSW parameters on dissimilar materials, namely AA6022 and cast magnesium alloy. Their study stated that increasing tool rotational speed causes an increase in failure loads. In addition, the plunge depth has a significant effect on shear load. Garg and Bhattacharya (2017) observed the mechanical properties, microstructure, and fractography of similar and dissimilar FSSW joints on aluminum and copper materials using constant variables of plunge depth, dwell time, and tool rotational speed. In the dissimilar materials of AA1060 and pure copper with a thickness of 2 mm each, dwell time was used in the FSSW joint process parameters. Research results have stated that intermetallic compounds form intermetallic compounds (Li et al., 2019). Like the research conducted by Mubiayi and Akinlabi. (2016), they analyzed the microstructure, tensile shear, and Vickers microhardness of dissimilar materials by varying the plunge depth, rotational speed, and tool geometries. Additionally, Avetand-Fènoël et al. (2020) successfully combined dissimilar materials such as aluminum and brass and aluminum and copper using a zinc interlayer to undergo an FSSW joint. However, similar aluminum AA1100, similar brass, and dissimilar AA1100 and brass have not been studied in FSSW joining. It is important to study the quality characteristics of micro FSSW joints on similar and/or dissimilar materials, such as maximum strength in single spot, two spots, and three spots. Hence, the purpose of this research is to investigate the lap shear force and microstructure of micro FSSW joints with similar aluminum AA1100, dissimilar AA1100–brass, and similar brass. The constant variables used were tool rotational speed, plunge rate, tilt angle and plunge depth, while the response variables studied were lap shear force and macrostructure and microstructure observed by an optical microscope. 

This research investigated the LSF and microstructure of micro FSSW joints. Similar and dissimilar materials were used, namely aluminum AA1100–AA1100, AA1100–brass, and brass–brass. The results of this study revealed the following: (1) In similar materials, the LSF was higher than in dissimilar materials. LSF on similar brass represented a significant increase in the number of spots, but for similar AA1100 materials, the increase in LSF was insignificant; (2) Macro- and microstructure in similar and dissimilar materials indicated the formation of a hook. As a result, on the similar AA1100, there was no visible flash formation. While at the dissimilar weld joint, AA110–brass micro FSSW created weak bonding metallurgy and formed a thin intermetallic compound that tended to microcrack.

The failure mode of plug shear failure was observed on similar materials, namely both AA1100–AA1100 and brass–brass. Interface failure, whereby aluminum left traces in the nugget zone of brass sheets, was observed in the dissimilar AA1100–brass material.

    This research is supported by the PUTI Q1 Research Grant from the 2020 program of the Directorate of Research and Public Services, Universitas Indonesia, with contract number NKB-4002/UN2.RST/HKP.05.00/2020.

Avettand-Fènoël, M.N., Nagaoka, T., Marinova, M., Taillard, R., 2020. Upon the Effect of Zn During Friction Stir Welding of Aluminum–Copper and Aluminum–Brass Systems. Journal of Manufacturing Processes, Volume 58, pp. 259–278

Badarinarayan, H., Yang, Q., Zhu, S., 2009. Effect of Tool Geometry on Static Strength of Friction Stir Spot-Welded Aluminum Alloy. International Journal of Machine Tools and Manufacture, Volume 49(2), pp. 142–148

Baskoro, A.S., Muzakki, H., Kiswanto, G., Winarto., 2017. Effects of Micro Resistance Spot Welding Parameters on the Quality of Weld Joints on Aluminum Thin Plate AA1100. International Journal of Technology, Volume 8(7), pp. 1306–1313

Baskoro, A.S., Hadisiswojo, S., Kiswanto, G., Winarto, Amat, M.A., Chen, Z.W., 2020. Influence of Welding Parameters on Macrostructural and Thermomechanical Properties in Micro Friction Stir Spot Welded Under High-Speed Tool Rotation. The International Journal of Advanced Manufacturing Technology, Volume 106(1-4), pp. 163–175

Bozzi, S., Helbert-Etter, A.L., Baudin, T., Criqui, B., Kerbiguet, J.G., 2010. Intermetallic Compounds in Al 6016/IF-steel Friction Stir Spot Welds. Materials Science and Engineering: A, Volume 527(16), pp. 4505–4509

Esmaeili, A., Givi, M.K.B., Rajani, H.R.Z., 2011. A Metallurgical and Mechanical Study on Dissimilar Friction Stir Welding of Aluminum 1050 to Brass (CuZn30). Materials Science and Engineering: A, Volume 528(22-23), pp. 7093–7102

Garg, A., Bhattacharya, A., 2017. Similar and Dissimilar Joining of AA6061-T6 and Copper by Single and Multi-Spot Friction Stirring. Journal of Materials Processing Technology, Volume 250, pp. 330–344

ISO 14273, 2000. Specimen Dimensions and Procedure for Shear Testing Resistance Spot, Seam and Embossed Projection Welds. International Organization for Standardization, Geneva, Switzerland

Li, G., Zhou, L., Zhou, W., Song, X., Huang, Y., 2019. Influence of Dwell Time on Microstructure Evolution and Mechanical Properties of Dissimilar Friction Stir Spot Welded Aluminum–Copper Metals. Journal of Materials Research and Technology, Volume 8(3), pp. 2613–2624

Li, W., Li, J., Zhang, Z., Gao, D., Wang, W., Dong, C., 2014. Improving Mechanical Properties of Pinless Friction Stir Spot Welded Joints by Eliminating Hook Defect. Materials & Design (1980–2015), Volume 62, pp. 247–254

Lin, Y.-C., Liu, J.-J., Lin, B.-Y., Lin, C.-M., Tsai, H.-L., 2012. Effects of Process Parameters on Strength of Mg Alloy AZ61 Friction Stir Spot Welds. Materials & Design, Volume 35, pp. 350–357

Mubiayi, M.P., Akinlabi, E.T., 2016. Evolving Properties of Friction Stir Spot Welds Between AA1060 and Commercially Pure Copper C11000. Transactions of Nonferrous Metals Society of China, Volume 26(7), pp. 1852–1862

Muzakki, H., Baskoro, A.S., Kiswanto, G., Winarto, W., 2018. Mechanical Properties of rhe Micro Resistance Spot Welding of Aluminum Alloy to Stainless Steel with a Zinc Interlayer. International Journal of Technology, Volume 9(4), pp. 686–694

Rao, H.M., Yuan, W., Badarinarayan, H., 2015. Effect of Process Parameters on Mechanical Properties of Friction Stir Spot Welded Magnesium to Aluminum Alloys. Materials & Design (1980–2015), Volume 66, pp. 235–245

Shen, Z., Yang, X., Yang, S., Zhang, Z., Yin, Y., 2014. Microstructure and Mechanical Properties of Friction Spot Welded 6061-T4 Aluminum Alloy. Materials & Design (1980–2015), Volume 54, pp. 766–778

Tiwan., Ilman, M.N., Kusmono., 2021. Microstructure and Mechanical Properties of Friction Stir Spot Welded AA5052-H112 Aluminum Alloy. Heliyon, Volume 7(2), pp. 1–16

Tutar, M., Aydin, H., Yuce, C., Yavuz, N., Bayram, A., 2014. The Optimisation of Process Parameters for Friction Stir Spot-Welded AA3003-H12 Aluminum Alloy using a Taguchi Orthogonal Array. Materials and Design, Volume 63, pp. 789–797

Yang, X.W., Feng, W.Y., Li, W.Y., Dong, X., Xu, Y.X., Chu, Q., Yao, S., 2019. Microstructure and Properties of Probeless Friction Stir Spot Welding of AZ31 Magnesium Alloy Joints. Transactions of Nonferrous Metals Society of China, Volume 29(11), pp. 2300–2309

Yazdi, S.R., Beidokhti, B., Haddad-Sabzevar, M., 2019. Pinless Tool for FSSW of AA 6061-T6 Aluminum Alloy. Journal of Materials Processing Technology, Volume 267, pp. 44–51

Yeni, Ç., Ozdemir, U., Sami, S., 2012. Effect of Pin Penetration Depth on the Mechanical Properties of Friction Stir Spot Welded Aluminum and Copper. Materials Testing, Volume 54(4), pp. 233–239

Zhou, L., Li, G.H., Zhang, R.X., Zhou, W.L., He, W.X., Huang, Y.X., Song, X.G., 2019. Microstructure Evolution and Mechanical Properties of Friction Stir Spot Welded Dissimilar Aluminum–Copper Joint. Journal of Alloys and Compounds, Volume 775, pp. 372–382