ILAS 2019: LIGHTWEIGHT CONSTRUCTION


between the dissimilar materials, enabling the size (and therefore weight) of the adapter to be reduced – a smaller connecting area between the materials is required. Tis, in addition to using the aluminium alloy in the deck constructions, can be used to reduce the weight (and therefore fuel consumption) of a ship. In the automotive industry, adapter


constructions are not used to join dissimilar metals, as sheets of aluminium alloy and steel can instead be welded together directly using lasers.


Forming a strong bond In both the automotive and shipbuilding industries, laser beam welding can be used to form a lap joint between two metal sheets (see Figure 1) made of steel and aluminium alloys. In this scenario the steel sheet has to be the upper joining partner, as using an aluminium alloy in this position would increase the aluminium content in the weld metal above permitted values, which would weaken the joint. In addition to controlling the mixing ratio of


the two materials in the weld metal, the penetration depth of the weld into the lower aluminium alloy sheet is also an important aspect of this process. By using a penetration depth that


is merely a little higher than the thickness of the steel material, a comparatively little amount of aluminium is enabled to be contained in the weld metal, so that the content of the intermetallic phases is limited. Each material and sheet thickness configuration requires a different appropriate penetration depth to achieve the best mechanical properties. At the Laser Zentrum Hannover, we have


successfully formed lap joints using dissimilar materials that are suitable for both the automotive and shipbuilding industries. For shipbuilding, a 5mm steel sheet (S355) was welded to an 8mm aluminium alloy (AA6082) sheet using a high-power diode laser beam source at 10.4kW laser beam power in a welding process with speeds of 1.9m/min. For automotive, a 1.5mm steel (22MnB5+AS150) sheet was welded to a 2mm aluminium alloy (AA6016-T4) sheet using a disk laser beam source at 3.75kW laser beam power in a welding process with speeds of 5.2m/min. In testing the mechanical properties of the


dissimilar joints, we found that for the shipbuilding configuration, a tensile shear force of up to 8.7kN could be withstood by a 25mm-wide sample before breaking, and for the automotive configuration, up to 3.2kN could be withstood by


a 22.5mm-wide sample before breaking. Using multiple joints, for example when an adapter configuration with six joints is used in shipbuilding, the tensile shear force that can be withstood can be increased by up to 88 per cent of the yield strength of the aluminium alloy base material. Despite these promising results, there is a gap


remaining, which has to be filled with knowledge about this innovative laser welding process, in order to enable the dissimilar joining of steel to aluminium alloys to be used for practical applications and products. Solving these challenges would provide many opportunities for a wide range of applications and uses. We will be working at the Laser Zentrum Hannover over the coming years in order to fill this gap.


Stefan Kaierle is the executive director of the Laser Zentrum Hannover.


Reference 1


https://ec.europa.eu/energy/en/topics/ energy-strategy-and-energy-union/2050- energy-strategy


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