Abstract
Brittle intermetallic phases are formed when steel and aluminum are joined. Therefore, it is difficult to use this combination of materials when applying the multimaterial design in the construction of load-adapted and weight-adapted structures. In order to largely avoid the formation of these brittle phases, joining processes based on diffusion processes, such as composite forging, depict a good solution approach. The materials are joined in a solid state. Furthermore, zinc additives are used to create the joint. Zinc forms a compound with both steel and aluminum without the formation of brittle phases. By combining the composite forging process with zinc additives, strength values of 26 N/mm2 can be reached. This is higher, in comparison to former investigations of resistance spot welded and clinched joints. The joint properties depend on the composition of the zinc interlayer. Small amounts of magnesium in the zinc interlayer affected the strength and ductility values. While the strength decreased by about 30% in contrast to the zinc layer without magnesium, the ductility increased by 60%. This effect was probably due to the metallurgical impact of the alloying elements on phase formation, as could be shown by energy dispersive X-ray spectroscopy (EDX) analyses of the joint zones. Thereby, it was shown that the brittle intermetallic phases are located only in small areas.
Highlights
Lightweight constructions in multimaterial designs significantly contribute to saving weight and resources
In the compound of aluminum and steel, brittle intermetallic iron-aluminum (Fe-Al) phases are usually formed during metallic continuity, especially because of a thermal joining process, due to the molten state [2,3]
Solid cylindrical aluminum bolts made of AlMg4.5Mn, and steel sheets of quality DX54 with zinc coatings of different chemical compositions were used for the production and investigation of dissimilar joints
Summary
Lightweight constructions in multimaterial designs significantly contribute to saving weight and resources. The coating of aluminum with zinc destroys the characteristic oxide layer This results in a better bond between the material surfaces [34] Since the zinc layer significantly contributes to the formation of the joint, this process is referred to as hybrid composite forging. This publication investigates the influence of the element magnesium in the zinc layer of the steel sheet on phase formation and on the strength and ductility properties. Within these tests, the aluminum bolts were first provided with a zinc coating by hot-dip galvanizing. On the basis of the compositions, an estimating classification was made with reference to the corresponding three-component systems
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