While Galvanized Steel Coil are inherently protected by their zinc coating, their surfaces typically undergo post-treatment to further enhance corrosion resistance, paint adhesion, and processing performance, or to impart specific functional properties.
Common surface treatment methods can be broadly categorized as follows:
Passivation Treatment
This process involves forming a protective film on the surface of the galvanized sheet, primarily to prevent the steel from developing "white rust" when exposed to moisture.
Chromate Passivation:
A traditional and widely utilized method. However, it involves hexavalent chromium, which is toxic and harmful to both human health and the environment.
Chrome-free Passivation:
A newer technology developed to comply with environmental regulations. It utilizes inorganic compounds-such as molybdates or silicates-or organic substances-such as silanes or resins-to create an eco-friendly passivation film.
Oiling Treatment
A layer of anti-rust oil is applied to the surface of the galvanized sheet to provide temporary corrosion protection. Since the anti-rust oil either evaporates over time or can be easily washed off, this method is suitable for sheets with short production cycles or those destined for subsequent cleaning processes.
Phosphating Treatment
Performed prior to painting, this process enhances the bonding strength between the galvanized sheet and the organic coating, while also improving overall corrosion resistance. It is particularly well-suited for applications requiring subsequent painting or coating. Hot-dip galvanized sheets typically undergo a surface conditioning step before phosphating to optimize the quality of the resulting phosphate film.
Untreated
This refers to maintaining the galvanized sheet in its original state-exactly as it appears after galvanizing-without any additional protective treatments. This approach helps reduce costs and is commonly applied to sheets intended for use as substrates for color-coating (pre-painted steel), thereby eliminating unnecessary expenses.
