ILAS 2019: LIGHTWEIGHT CONSTRUCTION


WELDING DISSIMILAR METALS IN THE SHIPBUILDING AND AUTOMOTIVE INDUSTRIES


In advance of his plenary presentation at ILAS, Dr Stefan Kaierle shares how the ability to join dissimmilar materials with laser beam welding could be used to decrease the weight of ships and cars, leading to a reduction in their carbon emissions


Tis article was co-authored by S Nothdurſt; O Seffer; R Lahdo; and J Hermsdorf of the Laser Zentrum Hannover.


I


n this day and age, the awareness of the importance of environmental protection and the conservation of resources is growing in people’s minds, the necessity is undeniable.


Terefore, several politic goals and tasks have been defined, for example in the European Energy Strategy 20501


. An important step in reducing Europe’s


greenhouse gas emissions will be reducing the emissions produced by the different branches of trade, particularly from the combustion engines of the vehicles involved. Two strategies are pursuable for reducing the emissions of vehicles with combustion


CO2


engines. Te first is the complete substitution of a lower-strength material in a component part with material of a higher strength, such as a high- strength steel. Tis enables a reduction in the thickness of the material being used, and therefore results in a lower weight for the component. Te second is the partial substitution of a material in a less loaded area of a component with a lighter material, with the lower strength of the new material still being sufficient to withstand the lower forces of the area. A material combination


which offers both high-strength and low-weight properties, is the combination of steel with an aluminium alloy. To realise hybrid components using this


Figure 1: Micrographs of metallographic cross sections of laser beam welded dissimilar joints of steel and aluminum alloys in shipbuilding (left) and automotive dimension (right)


successfully formed joints using dissimilar materials that are suitable for both automotive and shipbuilding


combination, the two materials have to be connected, however the thermal joining of dissimilar materials, such as steel and aluminium alloys is a challenging task. For one thing, they have very different chemical and physical


20 LASER SYSTEMS EUROPE ISSUE 42 • SPRING 2019


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properties – melting temperature, thermal expansion and thermal conductivity – and for another thing, there is a metallurgic challenge: during solidification, brittle intermetallic phases are formed in the weld metal, which reduce the strength and durability of the joint hugely. Furthermore, the stresses experienced by the welded metals during solidification cause cracking to occur. Due to its reduced and local


heat input, high intensity laser beam welding is an appropriate method for joining steel and


aluminium alloys. Te smaller weld pool and rapid cooling offer reduced diffusion and lower the mixing ratio between the two materials, enabling a stronger bond to be formed than that previously achievable using conventional thermal joining methods. In addition, its ability to be


automated enables this to be done with high productivity in series production. For automotive applications, parts made using


aluminium alloys can be used to lower a vehicle’s weight and reduce its fuel consumption. For shipbuilding, deck constructions made of aluminium alloys can be used to not only lower a ship’s weight, but to also lower its centre of gravity, which will increase its stability and driving speed. A large, oversized adapter construction has


previously been necessary to connect the aluminium parts of a deck construction to the steel hull of a ship. Explosion welding has been used to make this adapter in the past, which itself is made of dissimilar materials – the steel part of the adapter is welded to the steel hull of the ship, and the aluminium alloy part of the adapter is welded to the aluminium alloy used in the deck construction. By instead manufacturing the adapter using laser welding rather than explosion welding, a higher strength can be achieved


@lasersystemsmag | www.lasersystemseurope.com


Laser Zentrum Hannover


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