Laser soldering and brazing of steel-aluminum sheets for tailored hybrid tubes

Lightweight construction plays an important role in meeting the increasing demands of the automotive industry regarding weight reduction. In this work, two approaches have been chosen: weight reduction based on material and weight reduction based on design. Steel and aluminum are used for the first approach, and hydroforming is the method used for design optimization by shaping. Mixed material seams of steel and aluminum have been generated using laser soldering and laser brazing to make steel-aluminum tailored hybrid tubes for hydroforming. The seam has to provide sufficient formability and strength. The main difficulty in joining steel and aluminum is the formation of intermetallic phases, and these hard and brittle phases have to be avoided to ensure good forming properties. Pyrometric temperature detection for power control and longitudinal beam oscillation can provide an appropriate temperature-time profile to reduce the heat input, and consequently the intermetallic phases. Tests have been performed for joining aluminum (EN AW-6xxx, EN AW-7xxx) and two different galvanized steels. The sheet thickness was 1 and 2 mm for each material, and combinations of the same and different sheet thicknesses were tested. Another variation is edge preparation for different geometries and qualities. In this paper, the results of the joining process are described.