1.What are the differences in corrosion resistance characteristics of different coating types?
GA coating (galvanized aluminum): contains 5%~11% aluminum elements, forming a dense Al₂O₃ oxide film, with salt spray resistance 2~3 times higher than pure zinc coating (GI), and better scratch resistance.
Zn-Ni coating (zinc-nickel alloy): When the nickel content is 13%~18%, the salt spray resistance can reach more than 2000 hours, and the coating has high hardness (HV≥500) and strong stone impact resistance.
Zn-Mg coating (zinc-magnesium alloy): contains 1%~3% magnesium elements, generates Mg (OH)₂ corrosion inhibition layer during corrosion, has strong self-repairing ability, and is suitable for direct use without coating.
Composite coating (such as Zn/Zn-Ni double layer): The bottom pure zinc (thick coating) provides basic corrosion protection, and the surface zinc-nickel (thin coating) improves the surface hardness and corrosion resistance, with excellent comprehensive performance.
2.How to provide corrosion resistance through pretreatment and coating process optimization?
Degreasing and cleaning: Ultrasonic cleaning + spraying combined process is used to ensure that there is no stamping oil residue on the surface of DC03 appearance parts (oil film residue will cause the coating adhesion to decrease and cause early corrosion). • Cathodic electrophoretic paint (CED): The electrophoretic film thickness is controlled at 20~25μm. Using electrochemical protection (anodic protection), even if the coating is partially damaged, the electrophoretic paint can inhibit the corrosion of the substrate, which is especially suitable for crevice corrosion protection of Q235 structural parts.
3.How to provide anti-corrosion protection during the molding process?
The stamping die uses titanium nitride (TiN) coating to reduce the friction coefficient during stamping and reduce plating scratches (scratches are the starting point of corrosion). The plating integrity rate of DC03 deep-stamped parts has increased from 85% to 95%.
Timely coating after forming: Stamping parts are electrophoresed within 24 hours to avoid moisture and oxidation of the plating during storage (especially in an environment with humidity > 70%).
4.How to avoid corrosion of sensitive structures?
Reduce gaps and water accumulation: Design diversion grooves and drainage holes in vehicle doors, trunks and other parts to prevent rainwater from stagnating and causing crevice corrosion; the overlap gap of DC03 cover parts is controlled within 3mm and filled with sealant.
Electrochemical compatibility design: Avoid direct contact between galvanized parts and metals such as aluminum and copper (such as bolt connection) to prevent galvanic corrosion; if contact is necessary, use insulating gaskets (such as nylon gaskets) to isolate.
5.What is the systematic improvement strategy?
High value-added scenarios (such as exterior parts, high-end models): GA/Zn-Ni plating + chromium-free passivation + full-process coating protection is preferred to balance performance and environmental protection.
Cost-sensitive scenarios (such as economical vehicle structural parts): Thick hot-dip galvanizing layer + cathode electrophoresis + structural optimization to maximize cost performance.
Future trends: Develop towards chromium-free, low coating thickness and high corrosion resistance (such as Zn-Mg coating), digital process monitoring (such as online coating thickness detection), and develop thin coating + nano coating composite protection technology in combination with lightweight requirements.