Indian Journal of Chemical Technology Vol. 26, May 2019, pp. 248-251 Effect of current and welding time on tensile-peel strength of resistance spot welded TWIP 1000 and martensitic steels Volkan Onar 1 , Fatih Özen* 2,3 , Melih Kekik 2 , Yusuf Sadi Aslanlar 2 , Yüksel Özderin 2 , Hacı Aslan 2 & Salim Aslanlar 2 1 Faculty of Technology, Pamukkale University, Denizli, Turkey. 2 Faculty of Technology, Sakarya University of Applied Sciences, Sakarya, Turkey. 3 Faculty of Technology, Batman, Turkey. 4 Alimex Aluminium, Akyazi, Sakarta. E-mail: fatihozen@sakarya.edu.tr Received 28 January 2019; accepted 11 March 2019 Recently, to reduce car weight for saving fuel, reducing gas emissions, and to raise car safety by selecting the optimum material that meets desired mechanical properties, Advanced High Strength Steels (AHSS) have been continuously in development. TWinning Induced Plasticity (TWIP) steels, that have high tensile strength with high elongation, and Martensitic steels, which tensile strengths can be raised up to 1700 Mpa, are among the most significant members of AHSS. However, strength of joints as important as the material itself. In an automotive body, the most practiced joining method is resistance spot welding. Tensile-peel test in resistance spot welding is of high importance, because its behavior akin to the breaking action of the sheet metal at the time of the accidents. In this study, tensile-peel strengths are investigated in terms of current and weld time using resistance spot welding. The weld time range is selected between 5-30 periods (a period 0,02 sec) with 5 period increments. Keywords: Resistance spot welding, Tensile-peel strength, AHSS, TWIP, Martensitic steels Nowadays, reducing greenhouse gases and reducing car weight have been the main motivation of automotive industries 1 . Martensitic Steels (MS) have high tensile strength and low elongation ratio. It can be a solution both for automotive crash component and for reducing car weight. TWIP steels is another important material which has high elongation ratio and high tensile strength at the same material. And, thanks to this combination of mechanical properties, TWIP steels have been attractive for automotive companies and can be used on car bodies 2 . Among welding methods, Resistance Spot Welding (RSW) is the most utilized method for vehicle manufacturers to assemble sheet parts 3 . Also, RSW has a lot of advantages over other welding methods. For example, it is too cheap, does not require an additional weld metal, has low welding time and easy-to-adapt robotic/serial applications 4 . In a modern automotive, there are between 2000-5000 spot welds 5 . This quantity illustrates the importance of mechanical properties of RSW joints. All materials on vehicles selected by design conditions. However, mechanical performance of joints also should be taken into account, because, mechanical properties of RSW joints highly affect joined material failure and joining quality. In this study, tensile-peel strengths of TWIP/MS couples have been investigated in terms of different weld times and different weld currents. Also, separation modes have been evaluated. Experimental Section TWIP and MS sheets were welded by RSW method under constant cooling water flow rate and constant electrode force. Tensile-peel test executed to RSW applied specimens. Materials The Martensitic Steels (MS) having 1 mm thickness supplied from SSAB Turkey. TWIP steel having 1.4 mm thickness supplied from local dealer. Then, specimens sliced to 30×100 mm with Ermaksan hydraulic guillotine and ultrasonically cleaned. Chemical composition and mechanical properties of TWIP and MS have been presented in Table 1 and Table 2 respectively. The detailed dimensions of tensile-peel test specimen is presented in Fig. 1. Welding process and executing tensile-peel test A RSW machine having single lever pneumatic application mechanism with 120 kVA capacity were used in experiment. Current and timer values were adjusted with machine interface and continuously