A high performance galvannealed sheet steel has been developed by getting around some disadvantages. Coating adhesion primarily depends on the phase composition of the coating layer. Excessive galvannealing derives Gamma phase at the interface between steel sheet and coating. Gamma phase deteriorates the adhesion of the coating and causes powdering in pressforming. To eliminate the bad influences of Gamma, the galvannealing processes should be precisely controlled to produce the high performance galvannealed sheet steel. The influences of the content of Al in molten Zn bath and the temperature and the duration of galvannealing on the derivations of Gamma are studied and these conditions are optimized to get the most favorite coating free from Gamma for the automotive use. Additionally thin layer of Fe-P alloy is electroplated on the galvannealed sheet steel to avoid cratering defects in cationic electro-depositions painting. More than 3 g/m2 of the coating is necessary to get same anti-cratering property as that of cold rolled sheet steel. The galvannealed sheet steel which is produced under the processing conditions controlled precisely and electro-plated with Fe-P alloy has excellent properties in corrosion, welding and adhesion after painting, and is suitable for outer panels of automotives.
Development of high performance galvannealed steel sheet for outer panels of automotives
Entwicklung von galvanisiertem Hochleistungsstahlblech für die Außenbleche von Automobilen
1988
9 Seiten, 14 Bilder, 7 Tabellen, 6 Quellen
Aufsatz (Konferenz)
Englisch
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