MIG brazing method and mechanical properties of the unification of IF steel sheets

Interstitial free steels (if steels) are very suitable material for automotive industry and they are used for inner and outer body panel applications due to their high formability properties. They have extremely high formability characteristics under forming presses. Interstitials damages formability characteristics of steel. Elimination of interstitials (C and N) is achieved through careful control of the steelmaking process by the addition of titanium and/or niobium to react with carbon and nitrogen to form precipitates. In car assembly, where conventional welding processes like gas metal arc welding (GMAW) are used,the zinc coating is subject to severe evaporation and oxidation, leaving the weld bead and part of the base metal unprotected against subsequent oxidation. To reduce the risk of zinc evaporation, new welding processes with a low heat supply have begun to gain ground, for example MIG-brazing, which combines the advantages of the MIG process (high deposition rate, high welding speed and adaptable to automation) and brazing (without any intense fusion of the welded parts and without any appreciable alteration of the mechanical properties of the base metal and the coating applied). In this study, IF steel plates having 0,9 mm thickness were joined by copper-based CuAl8 wire in gas metal arc brazing technique. Specimens were prepared in two different joining forms as butt joint and overlap joint. Brazing operations were done with three different parameters, current intensities, travel speeds and shielding gas. Tensile strength, microstructure of brazed materials, and their micro hardness distribution throughout joining were determined. In macro and microstructure examinations, stereo optical microscope, scanning electron microscope (SEM), SEM/energy dispersive spectroscopy was used. This study investigated effects of current intensities, travel speeds and shielding gas on microstructure and microhardness distribution of transition zone between IF steel and brazed metal of joined material.