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Hybrid car bodies fabricated by joining parts made with steel and aluminum alloys are becoming increasingly common. This provides an affordable mean to decrease the car weight by using lighter or more advanced materials only where they can achieve the maximum benefit. This development is driven mainly by recent regulations on carbon dioxide emissions, and hinges on the deployment of effective joining technologies. In most cases, such technologies were not previously used in the car sector, and must be adapted to its requirements. Several dissimilar welding technologies, based on either fusion welding or solid-state welding, are reviewed here, focusing on dissimilar joining among steels and wrought aluminum alloys. These technologies are either presently being introduced in the car industry, or are used in other sectors and could be applied in the car industry in the near future.

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A 0.5 wt pct C, 22 wt pct Mn austenitic steel, recently proposed for fabricating automotive body structures by cold sheet forming, exhibits plastic localizations (PLs) during uniaxial tensile tests, yet showing a favorable overall strength and ductility. No localization happens during biaxial Erichsen cupping tests. Full-thickness tensile and Erichsen specimens, cut from as-produced steel sheets, were polished and tested at different strain rates. During the tensile tests, the PL phenomena consist first of macroscopic deformation bands traveling along the tensile axis, and then of a series of successive stationary deformation bands, each adjacent to the preceding ones; both types of bands involve the full specimen width and yield a macroscopically observable surface relief. No comparable surface relief was observed during the standard Erichsen tests. Because the stress state is known to influence PL phenomena, reduced-width Erichsen tests were performed on polished sheet specimens, in order to explore the transition from biaxial to uniaxial loading; surface relief lines were observed on a 20-mm-wide specimen, but not on wider ones.

Car bodies are increasingly made with high‐strength steels, for both lightweighting and safety purposes. Steel sheets, made by continuous casting, hot rolling, cold rolling, and continuous heat treating, are used to deep draw the car body parts, which are then joined by resistance spot welding (RSW). Two high‐strength automotive steels, with similar tensile strength, are studied here. The low alloy, dual‐phase steel consist of ferrite and martensite, obtained by an intercritical heat treatment, followed by fast cooling. The innovative, high‐Mn TWIP steel exhibits a promising combination of strength and toughness, arising from the austenitic structure, strengthened by C, and from the twinning induced plasticity effect. Tensile specimens are fatigue tested at room temperature with zero load ratio, both in the as‐fabricated (unnotched) condition and after the RSW of an homologous sheet square. Moreover, pre‐cracked compact tension specimens are tested with load ratio 0.1 to determine the fatigue crack growth behavior. These results are completed with crystallographic, microstructural, tensile, and fractographic examinations, and the influence of the microstructure and of the welding process is discussed.

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In this study, advanced high manganese austenitic steel sheets were welded by resistance spot welding at different welding parameters. The effects of welding current, clamping force, number of the current impulse, and duration of each current impulse were examined. Based on Taguchis method, an L-27(313) orthogonal array was employed for carrying out resistance spot welding tests. The welded sheets were subjected to tensile-shear tests in order to determine the strength of the welded joints. Basically, the results showed that tensile-shear strength increase with clamping force at the medium and high effective welding time (>400 ms). However, the occurrence of micro cracks within the welded joints may justify the scattering of tensile-shear strength values.

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