Q:What changes occur in mechanical properties after cold rolling and galvanizing?
A:After rolling, the cold-rolled steel sheet has finer grains and higher strength. At the same time, the hardness can be adjusted through the annealing process to meet different forming requirements.
The galvanized layer forms electrochemical protection with the substrate (zinc corrodes preferentially as an anode). Even if the surface is scratched, the zinc layer can still delay the corrosion of the substrate through the sacrificial anode effect.
Q:What changes occur in corrosion resistance after cold rolling and galvanizing?
A:Significant improvement in corrosion resistance
Protection mechanism of the galvanized layer:
Physical barrier: The galvanized layer isolates the substrate from the corrosive medium;
Electrochemical protection: The standard electrode potential of zinc is lower than that of iron, and it preferentially corrodes and protects the steel substrate.
Corrosion life comparison: Bare cold-rolled steel sheets rust in 24 hours in a neutral salt spray test, while cold-rolled galvanized sheets with a zinc coating thickness of 8μm can withstand salt spray for more than 200 hours;
Using zinc-iron alloy coating or zinc-aluminum-magnesium coating, the salt spray resistance can be improved to more than 1,000 hours, which is suitable for highly corrosive environments.
Q:What changes have occurred in surface quality?
A:Cold-rolled high-precision surface: The surface roughness of cold-rolled steel plate is low, the flatness is high, the coating is uniform after galvanizing, and there are no common defects such as scale and pitting of hot-rolled plate.
Surface treatment compatibility: The galvanized layer can be directly phosphated, painted, electroplated, etc.
Post-treatment: Phosphating treatment enhances coating adhesion (such as pre-treatment of automobile painting);
Electrostatic spraying or baking paint forms a composite protective layer (such as home appliance housing).
Q:What are the cost advantages compared with hot-rolled galvanized?
A:High material utilization rate: The surface quality of cold-rolled substrate is good, and the coating is evenly attached during galvanizing, reducing the waste of zinc liquid (the coating attachment amount of hot-rolled plate needs to be increased by 20-30% due to the influence of oxide scale).
Reduced processing cost: ◦ Cold-rolled galvanized sheet can be directly used for high-precision processing (such as stamping and bending), without the subsequent surface grinding and straightening processes of hot-rolled sheet, and the overall cost is reduced by 15-20%.
Q:What are the typical application scenarios?
A:Automobile manufacturing: body panels, chassis parts
Architecture and structural engineering: roof panels, wall panels, light steel keels
Home appliances and electronics: refrigerators, washing machine casings, electronic components