Q: Can galvanized coils achieve completely chromium-free passivation?
A: Absolutely. Chromium-free passivation technology for galvanized coils is quite mature and represents the current industry trend. Chromium-free passivation means completely eliminating chromium (including hexavalent and trivalent chromium) from the passivation treatment formula, using environmentally friendly alternatives composed of organosilanes, inorganic salts of titanium or zirconium, water-based acrylic resins, molybdates, etc. For example, a chromium-free passivation solution prepared using water-based acrylic resin and silica sol as film-forming agents, combined with molybdate as a corrosion inhibitor, can form a dense conversion film on the surface of the galvanized sheet, providing corrosion protection. Many large steel companies have already applied this technology in their large-scale production lines.
Second: Why has chromium-free passivation become an inevitable choice for the industry in terms of environmental regulations?
Answer: This is because the traditional hexavalent chromium passivation method faces global environmental regulatory restrictions. Firstly, hexavalent chromium is a recognized potent carcinogen, posing a serious threat to operator health during its production, and the resulting wastewater is a highly toxic and hazardous waste that is extremely difficult to treat. Secondly, at the international regulatory level, the EU's RoHS Directive and REACH regulations strictly limit the use of hexavalent chromium. For example, in the automotive industry, the EU signed a decree as early as 2003 prohibiting the use of hexavalent chromium in vehicle materials and components, stipulating that the hexavalent chromium content in each vehicle must not exceed 2 grams. Faced with these insurmountable environmental red lines, only chromium-free passivation processes, which have low environmental regulatory risks and fully meet the most stringent requirements of RoHS and REACH, have naturally become the fundamental way for companies to achieve compliant operations.
3. Is the protective performance of chromium-free passivation technology reliable?
A: Yes, it is reliable. Advanced chromium-free passivation technology can completely rival or even surpass traditional hexavalent chromium processes in terms of corrosion resistance. Organic/inorganic composite chromium-free passivation systems, represented by "silane coupling agent + titanium/zirconium salt," have a film-forming mechanism involving two core steps: First, titanium (Ti) and zirconium (Zr) ions are deposited on the zinc surface, forming an extremely thin, dense oxide conversion film as a framework; then, a special silane coupling agent and water-based acrylic resin cross-link to form a network organic film as an outer barrier, providing dual protection. In engineering test data, chromium-free passivated steel sheets with hot-dip galvanized iron alloys typically only develop red rust after 240 to 360 hours in salt spray tests, while traditional chromate passivated steel sheets show red rust after only 120 to 168 hours. This demonstrates that chromium-free passivated products actually have a longer service life. In humid heat stacking simulation tests, its anti-discoloration and anti-white rust period can reach 3 to 6 months, which can meet the stringent requirements of marine storage.
4. Are there any technical standards or specifications in my country for chromium-free passivation?
A: my country already has mature technical standards. The most important normative document is GB/T 41950-2022 "Metallic Coatings - Electroplating of Zinc and Zinc Alloys on Steel with Hexavalent Chromium-Free Treatment". This standard officially came into effect on July 1, 2023, and specifies the labeling requirements, process control, and minimum corrosion resistance and minimum coating thickness that must be achieved under specified test conditions for zinc and zinc alloy electroplating systems with hexavalent chromium-free passivation treatment on steel surfaces. This standard is based on the international standard ISO 19598:2016 and has been revised to incorporate several adjustments to meet China's actual application needs. In addition, the China Surface Engineering Association also published group standards such as "Chromium-Free Passivating Agent for Hot-Dip Galvanized Steel Sheets" in 2025, further promoting the standardization and popularization of chromium-free passivation technology.
5. What is the future development direction of chromium-free passivation for galvanized coils?
A: The core of future industry development lies in the complementary and synergistic effects of composite and multi-pronged approaches. Although single-component chromium-free passivation technology cannot achieve the comprehensive protective capabilities of chromates, significant and ideal results have been achieved in recent years by combining multiple technologies such as silicate passivation, rare earth passivation, titanium salt passivation, and organosilane passivation. Future research will mainly focus on finding more suitable material combinations to improve the self-healing ability of the passivation film, while further innovating the formulation system of organic/inorganic synergistic passivation. For applications requiring higher corrosion resistance, the industry is promoting a combination of "chromium-free passivator + sealant," achieving ultra-long salt spray protection of thousands of hours on medium carbon steel substrates through double-coating layering. It is foreseeable that with the continuous iteration of production processes and formulations, chromium-free passivation technology will completely eliminate harmful heavy metals while achieving precise and customized anti-corrosion performance.