Laser welding of aluminum for automotive applications

摘要

Aluminum Tailor Blanks have recently generated a lot of interest in the automotive industry. Aluminum offers significant weight and cost savings in car body manufacturing. The technology of forming Tailor Welded Blanks (TWB) for aluminum is challenging because of the difficulties associated with the welding and forming of aluminum. Present work describes the new findings and select results of laser processing of aluminum research done at the Center for Laser Aided Intelligent manufacturing (CLAIM), The University of Michigan. This includes the key experimental findings of the processing and characterization of laser-beam welding of Al 6061-T6 and 5754. A TRUMPF TLF 5000, Rf excited CO{sub}2 laser was used for laser welding. To overcome the common welding engineering problems such as sagging seam, undercuts and hot cracks, a novel filler material, Scandium modified 5025 Aluminum, was identified and used in laser welding. Various thicknesses of 6061-T6 and 5754 aluminum sheets were butt-welded using Sc filler material. Select results of the microstructural, geometrical and mechanical properties of the laser welds using Scanning Electron Microscope (SEM), X-ray Energy Dispersive Spectroscopy (XEDS), X-ray Diffraction (XRD) and tensile tests are presented. The Scandium laser welded joints showed high elongation. The crack failure in the tensile test shifted from the weld region to the base metal in case of Sc laser-welded 5754 and some 6061-T6 aluminum. Sc along with Zr forms very fine and coherent precipitates that inhibit recrystallization in aluminum alloys. The microhardness does not fall substantially in the fusion zone of Sc welded joints. The fusion zone shows a cellular dendritic structure. The grain boundaries are particularly seen in the boundary zone between the melted zone and heat affected zone (HAZ). HAZ cracking is significantly reduced in Sc laser-welded joints. The dispersion of thermally stable Al{sub}3Sc phase in the weld minimizes thermal softening that occurs in the HAZ. The welds under optimum conditions exhibited minimal loss of alloying element such as Mg. The welds made at higher speeds exhibited lower loss in Mg compared to the ones made at lower welding speeds. Composition of Helium and Argon in the top shroud plays a crucial role in determining the quality of weld. The flow rate of top and bottom shielding gas showed significant effect on the weld dimensions and appears to be very crucial for aluminum processing.