1.What are the requirements for coating thickness and uniformity?
Thickness requirements: Differentiated design based on the location of parts and anti-corrosion requirements. Generally:
External body panels (such as doors and hoods): 8-15μm (single-sided), which must take into account both anti-corrosion and appearance after painting;
Inner body panels (such as floors and pillars): 5-10μm (single-sided), focusing on basic anti-corrosion;
Parts in high-corrosion environments (such as chassis and wheel hub covers): 15-25μm (single-sided), which must enhance salt spray resistance.
Uniformity: The thickness deviation of the coating on the same plate must be ≤±2μm, and the thickness difference between the edge and the center must not exceed 3μm (to avoid local corrosion first).
2.What are the requirements for the bonding strength of the coating for electrogalvanized automotive plates?
The coating needs to be tightly combined with the substrate to avoid falling off during later processing or use. Testing requirements:
Bending test: According to GB/T 22319 standard, bend the plate 180° (the mandrel diameter is 2 times the plate thickness), and the coating has no peeling or peeling;
Scratch test: Use a scribing knife to scratch a 1mm×1mm grid, peel off the tape after sticking, and the coating shedding area is ≤5% (applicable to inspection before painting).
3.What are the requirements for corrosion resistance?
Neutral salt spray test (NSS): Depending on the requirements, the outer plate needs to pass 72-120 hours without white rust, and the inner plate needs to pass 48-72 hours without white rust; high corrosion resistance parts (such as zinc alloy layer) need to pass more than 200 hours without red rust (base corrosion).
Moisture and heat resistance: After being placed in an environment of 40℃ and 95% relative humidity for 1000 hours, the coating has no bubbling or rust.
4.What conditions must surface quality meet?
Appearance: no exposed bottom, pinholes, pits, scratches (depth ≤ 1μm), color difference, uniform gloss (gloss deviation of outer plate ≤ 5%);
Roughness (Ra): outer plate needs to be controlled at 0.8-1.6μm (to ensure the paint film is flat after painting), inner plate can be relaxed to less than 2.0μm;
Oil residue: surface oil content ≤ 5mg/m² (through wiping test or infrared spectrum detection to avoid affecting the adhesion of the coating).
5.What is the core process of electrogalvanizing?
Electroplating solution system: The mainstream adopts acid zinc plating (such as sulfate zinc plating and chloride zinc plating), among which the chloride system is more suitable for automotive plates with high uniformity requirements, and the current density can be controlled at 10-30A/dm².
Additives: Brighteners and leveling agents need to be added to ensure that the coating is bright and flat, and to avoid pinholes and burrs.
Current and temperature control: The current density needs to be dynamically adjusted according to the width and speed of the plate (for example, when the strip speed is 100-200m/min, the current density matches 15-25A/dm²).
Plating solution temperature: The chloride system is controlled at 40-50℃, the sulfate system is controlled at 20-30℃, and the temperature difference is ≤±2℃ (to avoid local uneven concentration).