TRIBOLOGICAL BEHAVIOR OF COMPOSITE ELECTRODES FOR SPOT WELDING Ionelia Voiculescu Materials and Welding Technology University Politehnica of Bucharest Bucharest, Romania ioneliav@yahoo.co.uk Victor Geanta, Elena-Manuela Stanciu, Vasile Ion Mihai victorgeanta@yahoo.com Elena.manuela.stanciu@gmail.com vasileionmihai@yahoo.com Tiberiu Laurian , Georgiana Chisiu Machine Elements and Tribological Department University Politehnica of Bucharest Bucharest, Romania tlaurian@gmail.com Georgiana_bosoi@yahoo.com Abstract — The paper presents some aspects regarding tribological characteristics of composite tops of the electrodes for spot welding. The solution aims to improve the resistance to deformation and high intensity electric current conductibility without loses and excessive local heating. The composite material was obtained by mechanical alloying process, from a mixture of tungsten carbide, chromium, CuNiAl alloy and cooper powder which has been heated in furnace at 1100 o C. The embedding process aims to avoid the toxic effects of metallic elements such as Be and Zr, which are usually introduced in cupper alloys for improving the mechanical characteristics. The tribological characteristics and microhardness of the melted zone were measured in order to estimate the strengthening effect obtained by the tungsten carbide presence for different mixture recipe. Keywords-wear; electrode; cooper; carbide I. INTRODUCTION In the spot welding process, thermal conditions at the two main interfaces, the faying surface, which is the workpiece/workpiece interface, and the electrode/workpiece interface, are particularly critical. The faying surface temperature affects the size and quality of the welds. Since excessive heating at the electrode/workpiece surface gives rise to cap deterioration, for a long electrode life the temperature should be kept as low as possible, while maintaining a higher temperature at the workpiece faying surfaces [1]. During welding, the electrodes tops are affected by plastic flow due to heating by JOULE effect under the action of the working pressure and the abrasion, the relative movement of material between the pair of electrodes in successive positions of welding. Some adjustment of the electrodes tops are necessary after a working period, depending on the base material and geometry of the welded parts, which conducted to reducing the active area or replacement of the tops. In general, the electric resistance of the electrode for welding, reported in the relative conductivity of copper, is recommended to be 0.7, the hardness 160 HB and the recrystallization temperature of 200 ° - 250 °C. For welding of austenitic and refractory steels, hardness should be much higher and the relative conductivity at least of 0.75. The mild steel can be welded using electrodes with hardness of 120-140 HB and a minimum relative conductivity of 0.8, while for light alloys, the recommended hardness are 100 HB [2]. Copper matrix composites are increasingly being used in a variety of components where high electrical and thermal conductivity, good corrosion and wear resistance were required, such as continuous casting mould, electrodes for spot welding, and the nozzle of CO2 gas shielded welding. Electrodes used in spot welding promote rapid wear, subsequently reducing electrode life. The incorporation of particulate reinforcements improves mechanical properties as well as wears resistance of the composites by acting as load-bearing components, while retaining considerably high conductivity [3]. Electrode wear adversely affects the cost and productivity of automotive assembly welding due to reduced weld quality, reliability, and robustness. This mandates increased inspection rates and greater control of welding parameters. Consequently, large potential cost savings and quality improvements are expected from substantial improvements in electrode life [4]. In order to increase the electrodes’ durability, the main methods proposed to create the thin composite layers can be pulverization of the melted metal in which ceramic particles are embedded, facing with band electrodes of carbides composite core using the induction effect as a thermal source, deposit of thin straps (bands) obtained through ultra-