How to correctly choose color-coated steel plates has always been a problem that troubles users of color-coated steel plates. Not only do most owners not know how to choose color-coated steel plates, but even many companies that produce color steel plate profiles and construction companies are not very familiar with this.
Most customers focus only on the coating requirements when selecting color-coated steel plates, often neglecting the substrate requirements. In fact, the corrosion resistance of the substrate is key to the corrosion resistance of color-coated steel plates. The thicker the zinc layer, the harder it is for corrosive media to penetrate the coating and reach the steel plate, thus improving the corrosion resistance of the color-coated steel plate.
In addition, the thickness of the coating is also a key factor affecting the corrosion performance of the cut of the color-coated steel plate. Notch corrosion is electrochemical corrosion. Influencing factors include the pretreatment layer, primer, substrate thickness, coating thickness, etc.
Generally, the pretreatment layer and primer are relatively fixed, while the thickness of the substrate and the coating will affect the cutting corrosion performance. The thinner the substrate and the thicker the coating, the better the resistance to notch corrosion.
Regarding this, there are many studies in the world, and the more widely accepted is the zinc ratio. That is, the grams of coating weight per square meter on one side of the coating / thickness of the substrate (mm). It is believed that a zinc ratio greater than 100 is a guarantee to effectively prevent cutting corrosion of color-coated steel plates. For example: if the steel plate is 0.6mm, the galvanized amount on one side needs to reach 60g/m2.
Although the corrosion resistance of aluminum-zinc coated is better than that of hot-dip galvanized, the zinc ratio is also used for hot-dip aluminum-zinc steel plates regarding notch corrosion.
As for whether the substrate should choose hot-dip pure zinc or hot-dip aluminum-zinc, it mainly depends on the pH value of the environment. Zinc and aluminum are both amphoteric metals, but their performance in acids and bases is different.
In alkaline media, the performance of pure zinc is better than that of aluminum-zinc alloy. The performance in acidic media is exactly the opposite, with hot-dip aluminum-zinc outperforming hot-dip galvanized.
Therefore, in the process of selecting color-coated steel plates, we recommend using aluminum-zinc coated color-coated steel plates in relatively acidic environments. For relatively alkaline environments, we recommend using hot-dip galvanized color-coated steel plates.
In addition, based on experience, do not allow aluminum-zinc coated substrates to come into prolonged contact with damp wood and concrete.
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