SECC vs SGCC: Electro or Hot-Dip Galvanised

Both grades are galvanised steel; the difference is how the zinc got there and how much of it there is. Electro-galvanising deposits a few microns — uniform, spangle-free, made for paint and thin walls. Hot-dipping builds a coating ten times thicker, bonded through an iron–zinc alloy layer, made for weather. Everything in the comparison follows from that thickness gap.

Reviewed by Tom, Senior Process Engineer·Dongguan source factory · 11+ years in precision sheet metal

steel secc vs sgcc comparison — SECC vs SGCC

Two coatings, two purposes

SECC's electro-zinc (around Z04–Z10, a few microns per side) exists to be unobtrusive: thin enough to weld, bend and paint exactly like bare steel, uniform enough that electronics manufacturers made it the indoor default. Its protection reserve is real but shallow — sized for indoor air and paint systems.

SGCC's hot-dip layer (Z80 and heavier classes) exists to survive: a metallurgically bonded zinc blanket that corrodes slowly outdoors and, crucially, sacrifices itself at scratches and cut edges to protect the exposed steel. That sacrificial mechanism is why galvanised parts tolerate real-world damage far better than painted bare steel — the coating keeps working after a chip that would doom a painted part.

Side by side

Criterion	SECC (electro)	SGCC (hot-dip)
Coating	A few µm per side, uniform, spangle-free	Z80+ — ~10× thicker, metallurgically bonded
Corrosion mechanism	Barrier — thin reserve	Barrier + sacrificial at damage
Indoor electronics duty	The default	Overkill; heavier coating at tight bends
Outdoor duty	Not designed for it	The purpose — inland at Z80, heavier for coastal
Bending	SPCC-class radii, no flaking	Radii ≥ 1× thickness to respect the coating
Surface	Bright, uniform — paint or bare as designed	Spangle pattern; usually painted outdoors
Welding	Standard with extraction	Standard with extraction; touch-up at welds outdoors

SECC vs SGCC for sheet metal duty

The outdoor line, drawn precisely

SECC outdoors fails in the predictable way: the thin reserve consumes itself, first at scratches and cut edges, then generally. The timeline depends on the climate, which is why we quote duty rather than a blanket year count — but the design intent is unambiguous. SGCC is the grade for weather.

Within SGCC, the coating class is the specification that matters. Z80 covers typical inland outdoor enclosure duty; coastal, industrial-aggressive or severe-exposure projects quote heavier classes. Naming the installation site in the RFQ sizes the coating correctly — it is the cheapest line item on the drawing and the one that decides field life.

Indoor, the comparison mostly evaporates

Indoors, both grades protect adequately, and the decision reverts to fabrication and appearance. SECC's uniform bright finish and thin coating make it the better citizen for thin walls, tight bends and paint systems. SGCC's spangle telegraphs through thin paint films and its coating stiffens very tight bends — both manageable, both reasons the electronics industry standardized on SECC for interior hardware.

Cost sits in the same register for both; the coated-sheet premium over bare SPCC is similar, and either grade's real economic comparison is against "SPCC plus a plating step" rather than against each other.

Fabrication notes that matter to buyers

Both grades laser-cut and weld in the standard mild-steel window with zinc-fume extraction
SGCC cut edges and weld zones get zinc-rich touch-up on outdoor parts — a two-minute step that keeps the sacrificial network continuous
SGCC bend radii stay at or above one material thickness; SECC takes SPCC-class radii
Painted outdoor parts are "SGCC substrate + powder top coat", with pretreatment and film build specified per project — two layers doing two jobs

Frequently asked questions

Can SECC be used outdoors if painted?

We advise against specifying it that way. Paint over SECC improves things, but the design reserve is thin, and any scratch or crevice reaches marginal zinc. For outdoor duty we quote SGCC — under paint if a colour is required — because the sacrificial mechanism is what survives damage.

What do Z80 and Z10 actually mean?

Coating mass in grams per square metre (total, both faces) for the zinc layer. Z10-class figures describe SECC's thin electro-layer; Z80 and heavier describe SGCC hot-dip classes. The number is the single best proxy for outdoor life — tell us the site and we size it.

Why does SGCC need bigger bend radii than SECC?

The hot-dip layer is thicker and micro-cracks at very tight bends, which can seed white rust at the bend line. Radii at or above one thickness keep the coating intact. SECC's thin layer bends at bare-steel radii without issue.

Is SGCC's spangle a defect?

No — it is the crystallisation pattern of the zinc as it solidifies, and it varies visibly between mills. On unpainted parts that is a sample-panel conversation at quotation; on painted outdoor parts it disappears under the specified film build.

Which one for an outdoor telecom cabinet?

SGCC, powder coated, with the coating class matched to the site — inland Z80-class as the default, heavier for coastal or industrial exposure, and zinc-rich touch-up at welds. That is the standard outdoor cabinet build we quote, and the one that survives the field.