Investigation on colourisation regularity of colouring hot dip galvanisation processing

The colouring hot dip galvanisation is a new hot galvanising processing. In this processing, a colour oxide film would be developed directly on the coating of the galvanised steel by the preferential oxidation of the additions in the hot dip galvanisation coating after hot dip operation. Due to their oxygen potentials and their oxide film properties, manganese and titanium were selected as additional elements in the colouring hot dip bath respectively. The influences of processing parameters on the colouring of coating were investigated systematically for the various binary Zn-Mn or Zn-Ti hot galvanising baths. The experimental results indicate that the colours on the coating of the galvanised steel would change continuously during its cooling period after hot dip operation. In the case of Zn-Mn bath, the possible colour tones of the oxide film are blue, yellow, purple and green, and their colour tones and the duration time varied with the manganese percentage composition and the hot dip temperature. In the case of Zn-Ti bath, the possible colour tones of the oxide film are blue, yellow and purple. However, titanium percentage composition in Zn-Ti bath has hardly effect on colouration regularity.