L. Zortea

Influence of dipping time on cracking during bending of hot dip galvanized coatings with Sn and Ti contents

In the last years, the attention to environmental topics led a new approach solution in classical protection techniques, introducing innovative way oriented to optimize different coating properties. Hot-dip galvanizing is a classical process aimed to generate coatings on iron-based surfaces, used unchanged since 200 years: some chemical elements are added in the bath with different aims (e.g., Pb is really important for its fluidizing properties, sometimes replaced by Sn) but sometimes these elements are dangerous for human health (e.g. … Pb!). In this work, the influence of dipping time and coatings chemical compositions on damaging micromechanisms was investigated considering different Sn and Ti contents. Main damaging micromechanisms in hot dip zinc coated ipersandelin steel specimens were investigated by means of bending tests. Longitudinal sections of bended specimens were observed by means of a LOM (Light Optical Microscope): main damage micromechanisms were identified as longitudinal and radial cracks.

Colorimetric variation of zinc–titanium alloy coatings

The purpose of this work is to characterise the colours obtained on the surface of zinc–titanium alloy coatings. Hot dip galvanising samples were prepared at temperatures in the range of 560–640°C. Seven colours were observed and objectively measured by means of reflectance curves and CIELab coordinates. Experimental results show that, after the extraction from the bath, the colours of the galvanised coating change continuously during the cooling and then stabilise after a few seconds. The colour uniformity on the surface of each sample was evaluated according to ASTM standard. Results show little colour differences in two specimens and acceptable colour uniformity in the other five.

Colour resistance of Zn–Ti coatings to corrosive environments

Adding titanium to a hot-dip galvanising bath, a coloured oxide film due to interference effect was obtained on iron samples; different colours were achieved varying the bath temperature in the range of 520–600°C. In this paper, the resistance of three colours (yellow, purple and light blue) to four corrosive environments (urban, marine, industrial and rural) has been investigated by means of an experimental approach: two specimens of each colour with titanium percentage of 0.2% were exposed for 1 year in each environment and colour measurements in CIE Lab coordinates have been recorded at fixed time intervals. Modification of colours on samples due to corrosion effects of different chemical agents was evaluated calculating CIE colour difference. Results demonstrated that the colour of the coatings have a good resistance to all kinds of atmospheres tested; so the performance of this galvanising bath resulted adequate for architectural application.