1.What are the main causes of white rust?
Continuous effect of humid environment
If the surface of the galvanized layer is in a high humidity environment (relative humidity>85%) for a long time, moisture will form a water film on the surface. When oxygen, carbon dioxide or other impurities (such as salt and dust) in the air are dissolved in the water film, it will form an "electrolyte" for electrochemical corrosion. Zinc acts as an anode and undergoes an oxidation reaction: Zn - 2e⁻ → Zn²⁺
The generated zinc ions combine with OH⁻ in the water film to form zinc hydroxide, which is then dehydrated to form zinc oxide, and finally appears as a white and loose rust product (white rust).
Residual moisture is not removed in time
If the galvanized parts are not completely dried after processing, the residual moisture on the surface will become the starting point of corrosion;
When condensed water is encountered during storage or transportation, the moisture accumulates on the surface and cannot evaporate, which can easily cause local corrosion.
The presence of corrosive media
Gases such as sulfur dioxide and hydrogen sulfide in industrial environments, or chloride ions in the air in coastal areas, will accelerate the conductivity of the electrolyte and significantly increase the corrosion rate;
Contact with liquids containing acids, alkalis, and salts will directly destroy the passivation film on the surface of the zinc coating and cause white rust.
2.What are the preventive measures for white rust?
Control environmental humidity and ventilation
Warehouses storing galvanized parts must be well ventilated and relative humidity must be controlled below 60%;
Dehumidifiers can be used in humid areas to avoid stacking galvanized parts directly on the ground (they need to be raised off the ground, such as using wooden racks or pallets) to prevent ground moisture erosion.
Ensure the surface is dry and clean
Galvanized parts need to be thoroughly dried after processing (such as hot air drying, natural drying) to avoid residual moisture;
Before transportation or storage, remove dust, oil and other impurities on the surface to reduce the "carrier" formed by the electrolyte.
Strengthen protective packaging
For galvanized parts that are stored or transported for a long time, moisture-proof paper or plastic film can be used for sealed packaging to isolate air and moisture;
In coastal or highly corrosive areas, desiccant (such as silica gel) can be placed in the packaging to further reduce local humidity.
Optimize the passivation and post-treatment process
Ensure the quality of the passivation film: control the concentration, temperature and treatment time of the passivation solution to ensure that the passivation film is uniform and dense;
For products with high requirements, an additional layer of varnish or anti-rust oil can be applied to form double protection (pay attention to the compatibility of the paint layer and the galvanized layer).
Avoid contact with corrosive substances
Galvanized parts should be kept away from acid and alkali solutions, salt-containing dust, and industrial waste gas sources;
Avoid direct contact with sweaty hands when transporting to prevent salt residue in sweat.
3.How to deal with slight white rust?
Wipe gently with a dry cloth or brush to remove loose white rust powder on the surface;
If there are traces left, wipe with a rag dipped in a small amount of neutral detergent (such as soapy water), then rinse with clean water and dry thoroughly;
After drying, spray a thin layer of anti-rust oil or varnish to restore the protective performance.
4.How to deal with moderate white rust?
First, use fine sandpaper or abrasive cloth to gently polish to remove rust products and expose the fresh galvanized layer;
After polishing, clean the surface with alcohol or water, perform passivation treatment after drying, and then apply anti-rust oil to seal.
5.How to deal with severe white rust?
In this case, the galvanized layer has lost its protective effect and the rust needs to be completely removed;
If the substrate is exposed after treatment, it needs to be re-galvanized or painted with anti-rust paint, otherwise the steel substrate will rust quickly.