from the conferences organized by TANGER Ltd. provisional website
This paper presents the research focused on surface defects of galvannealed car body sheets. The fragments of a car bonnet panel after press forming as well as steel sheet used for its production in as-delivered condition (prior to press forming) were investigated. The fragments of the sheet at the beginning, center and end of a coil and also from the left side, center and the right side of steel bandwidth were studied. The assumed scope of studies has covered the investigations of zinc coating morphology, studies of zinc adhesion, steel sheet material formability tests, scratch tests, defects analysis, and analysis of steel sheet material in terms of its usability for zinc coating. The fragments of a car bonnet panel were cut out in the spots where defects, i.e. protrusions, have been found. Defects defined as protrusions occurred as a result of particle or particles conglomerate depositing on the surface of the die. Particles causing protrusions were identified both as steel fragments most likely originating from steel sheet sheared by the edge of the die, and fragments of spalled zinc coating, most likely in the form of conglomerates. Moreover, the chemical composition of steel, especially too large silicon content, may also be the reason of easier spalling of fragments of zinc coating. The investigations also showed, that non-woven fabric used for cleaning the dies surface contained the particles, the presence of which on the surface of the dies can be considered as the origin of defects.Keywords: Galvannealing, car body sheets, press forming, zinc coating
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