Resistance spot welding has significant role in the joining technologies of automotive industry. In the recent period there were some rival technologies, but resistance spot welding remains important. This has numerous reasons however mass production is one of the main motivations. The applied base materials both steel and aluminium develop rapidly. The dual-phase (DP) steels with different strength are typical in the automotive chassis, and the high strength aluminium alloys also continuously spread. These special material combinations mean new challenges for joining technologies, sometimes hybrid aluminium - steel joints should be prepared. In this paper hybrid joints between DP800 steel and 5754-H22/6082-T6 sheets were prepared. The microstructural and strength properties of the joints were investigated and compared. An intermetallic compound was formed between the dissimilar sheets during welding which is basically determine the joint properties.

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In recent decades the toughness of welded structures becomes more and more important. This trend is particularly valid for the advanced high-strength steels (AHSS), which have reduced toughness comparing to the low-strength structural steels. Dynamic characteristics of the welded joints of the newly developed high-strength steel sheets required by the automotive industry have been neglected, with welding procedures being optimized on the static joint properties, mainly on the tensile-shear force. Up to the present time, testing of dynamic properties of the spot-welded joints has been performed by increased testing speed during tensile testing. The authors have developed a new dynamic testing method and designed new testing equipment for impact bending, which can give a numeric result to characterize the resistance of spot-welded joints against dynamic load. In this paper, this method will be used to evaluate resistance spot-welded joints made on DP600 and DP800 steels with three different technological parameters, comparing long-time welding, short-time welding, and two-pulse welding. The different parameters cause different weld nugget sizes, failure modes, impact energies, and force–time diagrams. All test results show that bigger weld nugget diameters cause better impact energies and impact forces, but the differences are not perfectly correlated.