1.Cold-dip galvanized coils form a zinc layer through electrolytic deposition. What effect does this have on processing performance?
Directly reduces pre-treatment steps before painting.
Due to surface spangles and slight roughness, hot-dip galvanized coil requires multiple pre-treatments before painting, including grinding, degreasing, and phosphating. Cold-dip galvanized coil, on the other hand, has a smooth surface, and the passivation film (such as chromate passivation) inherently adheres to the substrate, allowing it to serve directly as a paint primer without the need for additional sanding or priming. This makes it suitable for applications such as home appliance housings and automotive body topcoats. This not only reduces processing time and costs, but also avoids zinc layer loss caused by grinding, ensuring corrosion resistance.
Improving Forming Consistency in Precision Stamping
In precision stamping applications such as small electronic component brackets and connector terminals, surface flatness directly impacts the fit between the die and the steel strip. Spangle protrusions on the surface can easily lead to uneven localized force during stamping, resulting in burrs on the workpiece edges and dimensional deviations. The flat surface of cold-dip galvanized coil ensures uniform die pressure, ensuring dimensional consistency in batch stamping and reducing scrap.
2.What effect does a thin zinc layer have on bending or deep drawing properties?
No risk of zinc peeling during bending.
During the repeated 90°/180° bending of shelf columns and distribution box frames, the thin zinc layer deforms synchronously with the substrate (with an elongation of over 20%), preventing cracking or peeling due to zinc brittleness. In contrast, the thicker zinc layer of hot-dip galvanized steel can easily break apart and expose the substrate to rust due to the large difference in deformation between the substrate and the zinc layer during bending. The thin zinc layer of cold-dip galvanized steel ensures overall corrosion resistance after bending, eliminating the need for subsequent repainting. Deep drawing processes are less prone to "zinc layer embrittlement and cracking."
In deep drawing applications, such as refrigerator door panels and automobile door inner panels, the workpiece undergoes extensive tensile deformation. If the zinc layer is too thick or has poor ductility, it can easily separate from the substrate during stretching (forming "delamination") or crack at stress-concentrated areas (such as the edges and corners of door panels). However, the thin zinc layer of cold-dip galvanized coils adheres tightly to the substrate, stretching synchronously with it. The zinc layer's inherent ductility can absorb some of the tensile stress, preventing zinc layer failure after processing and reducing the cost of subsequent rust prevention treatments.
3.What is the corrosion resistance after welding/shearing?
Welding produces low zinc fume, and welds are corrosion-resistant and easy to repair.
In resistance welding/arc welding of steel structure brackets and automotive interior brackets, the thin zinc layer produces far less zinc evaporation than the thicker hot-dip galvanized layer. This reduces zinc fume pollution during welding (protecting operator health) and prevents weld porosity caused by excessive zinc vapor (ensuring weld strength). Furthermore, after welding, only local passivation or touch-up is required at the weld seam (exposed base material area). This, combined with the cold-dip galvanized coil's inherent passivation film, provides integrated protection, eliminating the need for extensive surface treatment and reducing post-processing maintenance costs. Cuts are less susceptible to rust after shearing/slitting. During the shearing/slitting process for narrow strips of hardware accessories and electronic components, the base material is exposed at the cut. However, the passivation film on cold-dip galvanized coil has a certain degree of mobility (some passivation agents can slightly cover the cut), and the thin zinc layer's "sacrificial anode effect" quickly protects the cut. Compared to hot-dip galvanized coil, which is prone to rapid rusting due to zinc shedding after shearing, cold-dip galvanized coil cuts do not require additional rust prevention treatment during short-term storage or light use, improving processing convenience.
4.What is the high-precision and low-loss processing performance of hot-dip galvanized coils?
High shearing/slitting precision and burr-free performance.
Low-carbon mild steel has a low hardness (HV ≤ 150), which reduces tool wear during shearing. Its tight dimensional tolerances ensure smooth, burr-free edges for narrow strips (e.g., under 50mm) after slitting. This makes it ideal for processing small hardware and electronic brackets, eliminating the need for subsequent burr removal and reducing processing steps.
Dimensional stability for precision bending.
For applications requiring precise bending angles (e.g., 90° ± 0.5°) such as air conditioner indoor unit frames and computer cases, the low hardness of the substrate minimizes post-bending springback (springback rate ≤ 2%). Its high dimensional accuracy ensures consistent angles across batches of bent parts, preventing assembly misalignment caused by high substrate hardness or dimensional deviations, and improving subsequent assembly efficiency.
5.What is the core logic of performance characteristics and processing adaptability?
Smooth surface → Suitable for painting and precision stamping (reducing pre-treatment);
Thin zinc layer + high ductility → Suitable for bending and deep drawing (avoiding zinc layer failure);
Metallurgical bonding + passivation film → Suitable for welding and shearing (ensuring corrosion resistance after processing);
Soft substrate + high precision → Suitable for precision shearing and bending (ensuring processing accuracy).