PSI - Issue 79

Benjamin Möller et al. / Procedia Structural Integrity 79 (2026) 493–500

495

from the steel S355 and the aluminum alloy AA6082, where a form fit by an undercut using two intersecting laser beams in addition to the firmly bonded welded joint is applied. While earlier investigations on the fatigue performance of LBW steel-aluminum lap joints focused on the resistance against shear loading, Möller, B. et al. (2017) and Möller, B. et al. (2019), the fatigue assessment of the developed LBW process realizing a form fit was made on steel-aluminum lap joints under orthogonal loading by Korschinsky et al. (2025), since this is the most critical loading direction. The present paper addresses the tensile and fatigue strength

of LBW steel-aluminum adapters with form fit. 2. Materials and welding method hybrid joints 2.1. Materials for steel-aluminum hybrid joints

The development of an innovative laser beam welding process for steel-aluminum adapters was carried out on dissimilar lap joints of the aluminum alloy AA6082 T651 (sheet thickness t = 12 mm) and S355 steel ( t = 5 mm) with the mechanical properties defined in Table 1. For the final adapter design and investigations, aluminum sheets of slightly differing thickness are used.

Table 1. Mechanical properties of applied materials.

Material

Yield strength R p0.2 [MPa]

Tensile strength R m [MPa]

Elongation at break A [%]

S355

431

527

28

AA6082 T651

276  284

326  334

17  18

When it comes to fusion welding, it is well known that the different physical properties of steel and aluminum as well as the low solubility of iron in aluminum cause some challenges which usually result in strength and formability limitations: • Formation of (brittle) intermetallic phases (Al x Fe y ) • Formation of cracks in the intersection between steel and aluminum It has been shown that the microstructure of the weld seam related to the aluminum content as well as the weld geometry at the intersection between steel and aluminum (e.g. weld depth) strongly influence the strength characteristic of the steel-aluminum-joint. Furthermore, the load case, i. e. the loading direction related to the weld, is of importance. While shear loading already shows a high strength potential, orthogonal loading of the sheet opponent to each other, e. g. realized by a bending load case, is the critical load case showing lower strength, caused by a missing form fit in previous investigations. 2.2. Laser beam welding This section addresses experimental setup, the development of laser beam welding processes, and adapter geometry for the production of adapters. The laser beam welding processes were performed using two fiber laser beam sources HighLightFL6000-ARM and HighLightFL8000-ARM (COHERENT, Inc.) with adjustable laser beam intensity with a max. output power P L of 6kW and 8kW. The laser beam welding processes were each performed by using a laser beam power of 6 kW. The laser beam sources emit a wavelength of 1,070 nm and are equipped with two optical fibers arranged one inside the other. The inner optical core fiber has a diameter of d C =70 μm and the outer optical ring fiber has a diameter of d R =180 μm. The power of the core beam is P C = 2 kW and P R = 4 kW for the ring laser beam, which can be adjusted independently of each other. The laser processing heads LPH-O (Scansonic MI GmbH) were each equipped with scanners and fixed to a three-axis portal system. For the optics, focusing lenses with a focal length of f f =500mm and collimating lenses with a collimation length of f c =172mm were used. Theoretical spot