In the present study, the improvement of the bond strength of galvanized steel sheets in the cold roll bonding process is investigated. Zn-Fe intermetallic compounds are employed as an intermediate layer. The galvanized low-carbon steel is cold roll bonded. Prior to the roll bonding, the sheets are heat treated in the temperature range from 450 to 550 8C. The influence of the heat treatment on the bond strength is investigated. It is found that the use of the pre-rolling annealing increases the bond strength. The highest average value is observed after a treatment at temperatures in the range from 450 to 500 8C. Higher temperatures, however, reduce the bond strength. The bond is analyzed by optical and scanning electron microscopy (SEM) and evaluated in a tensile shear test. The interaction between iron and zinc is considered to be responsible for the improved bond strength. The presence of intermetallic compounds in the interface zone forms a brittle layer, which is required to create juvenile surfaces due to local fracturing during the roll bonding.

The influence of a chemical or mechanical surface modification followed by different post-heat treatments on the bond strength of galvanized steel/aluminum composites is studied. An incremental rolling process is used for joint formation based on plastic deformation. The morphology, the chemical state of the modified surfaces as well as the cross-section, and local potential distribution of the welded zone is characterized by different microscopic and spectroscopic methods. The stability of the joint is analyzed by a shear-force test in combination with microscopic failure analysis. A clear correlation between pre/post-treatment and the joint strength is observed. 1709/16-2, HO 2356/8-2, and MA 1175/36-2 as part of the ECUF project (SPP 1640 framework). Special thanks are due to N. Buitkamp (CMP) for supplying the FE-SEM measurements.

The cold pressure welding of metals is a joining by forming technique capable of joining both similar and dissimilar metals in their solid state. In this article collective research on the cold pressure welding of metals with the aim of increasing both the overall weld strength and the weld-ability is presented. The application of innovative strategies based on electrochemical methods for an optimized conditioning of metal surfaces is investigated. The results account for a noticeable increase in the weld strength of steel-aluminum joints after a surface activation consisting of either an electrochemical roughening or electrodeposition of a bifunctional organosilane thin film. In addition to the surface activation process regimes for the preand post-welding heat treatment is investigated. Both weld strength and weld ability are improved due to heat treatments of steel sheets with various coatings and uncoated aluminium. The cold pressure welding is hereby done by incremental rolling, a new design process that allows for the manufacture of linear and curved joints between sheet metal blanks. Keywords: Electrochemical added joining of plates (ECUF) / incremental rolling / bonding agent / organosilane / heat treatment / intermetallic phases Das Kaltpressschweißen von Metallen ist ein Verfahren des Umformtechnischen Fügens mit besonders interessanten Möglichkeiten für Multi-Material-Verbindungen aus artfremden Metallen. Dieser Artikel beschreibt Untersuchungsergebnisse zum Kaltpressschweißen von artgleichen und artfremden Metallen mit dem Ziel die Verbindungsfestigkeit zu erhöhen und die erforderlichen Prozesskräfte zu reduzieren. Untersucht werden dazu Methoden der elektrochemischen Oberflächenaktivierung, der Wärmebehandlung der Fügepartner vor und nach dem Kaltpress-schweißen, sowie ein neuer Umformprozess zur flexibleren Herstellung der Fügeverbindungen, dem inkrementellen Walzen. Es wird gezeigt, dass die Verbindungsfestigkeit durch eine werkstoffspezifische Vorbehandlung mit elektrochemischen Methoden deutlich ansteigt. Darüber hinaus werden die Auswirkungen von Wärme-vor-und nachbehandlungen der Fügepartner untersucht und in den Untersuchungen an beschichteten Stählen und einer unbeschichtete Aluminiumlegierung gezeigt, dass eine gezielte Wärmebehandlung zu festeren Verbindungen führt oder diese erst ermöglicht. Mit dem inkrementellen Walzen wird dabei ein Umformprozess untersucht, der die Herstellung von linienförmigen Verbindungen zwischen artgleichen und artfremden Blechplatinen ermöglicht. Schlüsselwörter: Elektrochemisch unterstützes Fügen blechförmiger Werkstoffe (ECUF) / inkrementelles Walzen / Haftvermittler / Silane / Wärmebehandlung / intermetallische Phasen Joining of blanks by cold pressure welding Materialwiss. Werkstofftech.

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