INVESTIGATIONS OF THE STRUCTURE AND HARDNESS OF DISSIMILAR STEEL-TO-ALUMINUM JOINTS MADE USINGLASER WELDING TECHNOLOGY

Abstract

Since welding technology is currently used to assemble the frame of driver’s seats, it is important to develop laser welding technology for steel and aluminium. For this reason, the purpose of the present work was to examine the structure and selected properties of aluminium-steel joints using the example of an EN AW-6060 aluminium alloy and DC04 low-alloy steel welded in laser technology. Overlapping joints were made, weld type –following the hole laser welding method –laser beam (LB) using a high power disk laser (TRUMPF TruDisk3302), in which the active medium is a yttrium-aluminium crystal (YAG). Metallographic microstructure investigations were carried out using a light microscope from Carl Zeiss - Observer Z1m, and the weld microstructures were investigated using an SEM Supra 35 microscope, also from Carl Zeiss. The chemical composition analysis in micro-areas was carried out using an X-ray energy dispersion spectrometer from EDAX, which was a part of the SEM Supra 35. The hardness of the substrate material and the welded area was measured following the Vickers method using an FM-ARS 9000 micro hardness tester from Tokyo, Japan. It was found that there is a potential for commercial use of laser welding to make a low-carbon steel-aluminium alloy joint. During the formation of the weld in its microstructure, intermetallic compounds of the FexAly type were created, which significantly reduced the mechanical and plastic properties of the joint. The hardness of the weld created wasabout seven times higher than that of DC04 carbon steel. The choice of laser welding parameters (primarily, laser power and beam speed) significantly impacted the weld structure and properties.