Folami research: Optimization of steel-aluminum joints in shipbuilding

Welding Laser Beam Welding for High-Performance Steel-Aluminum Joints

2025-11-26 Source: Fraunhofer LBF | Translated by AI 2 min Reading Time

In the Folami research project, researchers at Fraunhofer LBF investigated the process-reliable production of thick-walled steel-aluminum mixed joints using laser beam welding. In doing so, they developed a method to evaluate steel-aluminum laser beam welded joints.

Experimental fatigue strength analysis for local fatigue strength evaluation of steel-aluminum weld seams using digital image correlation.(Image: Fraunhofer LBF) — Experimental fatigue strength analysis for local fatigue strength evaluation of steel-aluminum weld seams using digital image correlation.
(Image: Fraunhofer LBF)

In shipbuilding, especially in yacht construction, multimaterial joints are widely used when the lightweight material aluminum is combined with conventionally processed steel materials, for example, as a joining technique for the aluminum deck structure with the steel hull. This steel-aluminum mixed joint has so far been implemented in the form of so-called explosively welded adapters.

Laser beam welding can serve as an innovative welding method and alternative manufacturing technique in the future. This developed method produces form-fit and material-fit joints with significantly improved strengths, especially under tensile loads.

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The focus of the research work was on developing a methodology for evaluating the steel-aluminum laser welded joints and its implementation in a welded adapter.(Image: Fraunhofer LBF)

New Evaluation Solution With Simulation And Peak Stress Method

In the collaborative project Folami "Form-Fit Laser Beam Welding of Steel-Aluminum Joints for Durable Semi-Finished Products in Shipbuilding," researchers at the Fraunhofer Institute for Structural Durability and System Reliability LBF developed a methodology to evaluate steel-aluminum laser beam welds and implement them in a welded adapter. For this purpose, a local evaluation method, the so-called Peak Stress Method, was adapted to the application case of steel-aluminum joints using digital image correlation for strain alignment, and a local fatigue strength evaluation was achieved.

The experimental results show, in addition to increased fatigue strengths of the developed adapter semi-finished product, high tensile strengths close to the yield limits of the aluminum reference material EN AW-5083, indicating the effectiveness of the material and form fit.

AI-Supported Lifetime Prediction of Laser Beam Welds Between Aluminum And Steel

The newly developed evaluation procedure envisions correlating the welding seam parameters, such as connection width or penetration depth of the laser beam weld from EN AW-6082 T6 aluminum to S355 steel, with the fatigue strength derived from the Peak Stress Method and experimentally verified. To expand the data basis beyond the experimental results, parameter variations of the weld geometries and finite element load simulations were conducted to derive peak stresses. These were divided into training and test datasets and used to predict the service life with a neural network.

Transferred to Other Joined Metallic Multimaterial Connections

The research results provide an evaluation approach for this specific steel-aluminum hybrid joint, which also offers potential for transferability to other joined metallic multi-material connections. Companies in shipbuilding, vehicle manufacturing, as well as mechanical and plant engineering that work with hybrids benefit from these findings. The new evaluation methodology enables precise prediction of product lifespans and increases structural integrity.

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Date: 08.12.2025

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