Colored hot dip galvanization of various steel samples was realized in an
industrial bath containing 738 kg of a Zn-Mn liquid alloy at 450?C. Zinc was
alloyed in three steps to reach 0.1, 0.15 and 0.2 w% of Mn in liquid zinc,
and galvanization of 9 different steel samples was performed in all three
baths. The obtained colors change in the sequence blue - yellow - pink -
green with increasing the Mn-content of the bath and with increasing the wall
thickness of the steel samples. The results are analyzed by Glow-discharge
optical emission spectroscopy (GD-OES) and Secondary Neutral Mass
Spectrometry (SNMS) techniques. It is shown that depending on the Mn-content
and on the wall thickness of the steel the samples are coated by MnO of
various thicknesses (in the range between 30 - 230 nm). This layer forms when
the samples are removed from the Zn-Mn bath into surrounding air, before the
Zn-layer is solidified. Light interference on this thin MnO layer causes the
colors of the galvanized coating. Different colors are obtained in different
ranges of MnO thicknesses, in accordance with the laws of optics. The minimum
Mn-content of liquid Zn is found as 0.025 ? 0.010 m/m% to ensure that the
original outer ZnO layer on Zn is converted into the MnO layer. This minimum
critical Mn-content is in agreement with chemical thermodynamics.
Coloring hot-dip galvanization of steel samples in industrial zinc-manganese baths
