Hybrid compound forging as joining process for aluminum bulk parts and steel sheets

Project title Hybrid compound forging as joining process for aluminum bulk parts and steel sheets (Verbundhybridschmieden)
Project duration 01.03.2017 – 31.12.2018
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Press release

To reduce component weight, lightweight constructions and lightweight materials are increasingly applied. Especially in car manufacturing, compounds of steel and lightweight materials as aluminum and magnesium are used. However, the compound is usually generated by an extra joining step, e.g. welding, and presents problems such as increased corrodibility. Therefore, this research project studies the joining of bulk aluminum parts and steel sheets in a combined forming and joining process.

In this research project, a material bond between a bulk aluminum part and a steel sheet shall be generated by forming. The connection is to be made by zinc as plumb to prevent the generation of brittle intermetallic phases. By simulating the process and experimental tests, a suitable process field shall be identified. In a subsequent step, the hybrid part will be formed further to evaluate to what extend the compound is suitable for further processing. The research project is carried out in cooperation with the Institute of Welding and Machining of TU Clausthal.

Publications about the project

In lightweight automotive construction, hybrid structures made of various materials as well as solid and sheet metal elements are used. By hybrid compound forging, a sheet steel and a solid aluminium part can already be joined in a material-locking manner during the forming process. The Institut für Integrierte Produktion Hannover (IPH) gGmbH and the Institut für Schweißtechnik und Trennende Fertigungsverfahren (ISAF) of TU Clausthal are investigating how solid aluminium bolts and steel sheets can be joined in a material-locking manner. This article explains the decisive forming parameters. Furthermore, the tool design for the joining tests is presented.

lightweight construction, aluminum, compound forging

Lightweight automotive construction increasingly relies on hybrid structures made of steel and aluminium. These materials are currently joined mainly by form locking, for example by riveting. Welding and bonding are also used for joining the two materials. Hybrid composite forging allows to join the two components during the forming process. This shortens the process chain. With the help of zinc as a brazing material, the components are joined to form a material bond. This publication explains the results of the simulative parameter study. It shows how temperature, geometry and speed influence the joining result. Furthermore, first results of practical joining tests are presented.

lightweight construction, aluminum, simulative parameter study

In lightweight construction, light metals like aluminum are used in addition to high-strength steels. However, a welded joint of aluminum and steel leads to the precipitation of brittle, intermetallic phases and contact corrosion. Nevertheless, to use the advantages of this combination in terms of weight saving composite hybrid forging has been developed. In this process, an aluminum solid part and a steel sheet were formed in a single step and joined at the same time with zinc as brazing material. For this purpose, the zinc was applied by hot dipping on the aluminum in order to produce a connection via this layer in a forming process, under pressure and heat. Due to the formed intermediate layer of zinc, the formation of the Fe-Al intermetallic phases and the contact corrosion are excluded. By determining the mathematical relationships between joining parameters and the connection properties the strength of a specific joint geometry could be adjusted to reach the level of conventional joining techniques. In addition to the presentation of the joint properties, the influence of the joining process on the structure of the involved materials is also shown. Furthermore, the failure behavior under static tensile and shear stress will be shown.

lightweight construction, aluminum, joining properties

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The project no. 340490925 received funding from the German Research Foundation (DFG).

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