1.What is the difference in corrosion resistance between the two?
GI: Advantages: Thick zinc layer + alloy layer barrier, long corrosion resistance life (20-50 years outdoors), especially suitable for high corrosion environments (such as building roofs and bridges).
Disadvantages: The edges of zinc flowers are prone to corrosion first, and the incision protection is weak (painting is required for reinforcement).
SECC: Advantages: Uniform coating, good cut protection (uniform electrolytic deposition coverage).
Disadvantages: Thin zinc layer, low corrosion resistance (usually used in indoor environments), relying on surface passivation film (chromate) to prevent white rust.
2.What is the difference in machinability?
The GI zinc-iron alloy layer is hard and brittle, easy to powder and peel off, and requires large fillet and strong lubrication; the zinc layer on the outer side of the bend is prone to cracking, and the inner diameter needs to be ≥ 2 times the plate thickness; the thicker the zinc layer, the more serious the spatter/pore problem.SECC zinc layer has good ductility and processability close to that of cold-rolled plate, which is suitable for precision forming; it has excellent bending performance, and the inner diameter can be ≤1 times the plate thickness; the zinc layer is thin, and the welding difficulty is relatively low (but process optimization is still required).
3.What is the difference between surface quality and appearance?
GI: The zinc flower texture is obvious, and it is easy to reflect unevenly when directly exposed. It usually needs to be used after painting (such as color-coated plate substrate). The surface hardness is low (the Mohs hardness of the pure zinc layer is ≈2.5), and it is easy to scratch.
SECC: The surface is fine and texture-free, and can be directly used for visible parts (such as electrical housings and chassis). The passivation film provides matte/chrome-free environmentally friendly options. The hardness is higher (the hardness after plating is HV 50-70), and the wear resistance is slightly better.
4.What is the difference in coating adhesion?
GI: The zinc-iron alloy layer is porous, and the coating has strong adhesion after phosphating (especially suitable for architectural color coating).
SECC: The passivation film (chromate/chrome-free) provides excellent paint film adhesion and is widely used in spray/powder coating.
5.What are the special precautions?
Weldability: GI has a thicker zinc layer, and zinc evaporation is more intense during welding, requiring stronger parameter adjustments (such as a 20% increase in spot welding current).
Environmental protection: SECC's chromate passivation contains hexavalent chromium (RoHS restricted), and chromium-free passivation is a trend; GI production has high energy consumption, but there is no chemical waste liquid.
Design restrictions: GI avoids small fillet design (minimum bending radius ≥2t), SECC can withstand a smaller bending radius (≥0.5t).