Steel That Doesn't Rust. POSMAC.
Zn-Mg-Al tri-alloy coated steel supplied by POSCO. 5–10× the corrosion resistance of standard galvanized steel.
What Is POSMAC?
POSMAC is a zinc-magnesium-aluminum (Zn-Mg-Al) tri-alloy hot-dip coated steel developed and supplied by POSCO.
It offers 5–10× the corrosion resistance of standard hot-dip galvanized steel (GI), and its hard, formable coating stays intact through fabrication — so no post-galvanizing is required. This shortens the production cycle and reduces overall cost.
3S Co., Ltd. uses POSMAC in the Diet Cable Tray to ensure long-term durability in the harsh marine and offshore environment.
Why POSMAC?
5–10× Corrosion Resistance
Outperforms standard GI in salt-spray conditions by 5–10×. Optimized for the demanding corrosive environment of marine and offshore applications.
Forms Without Cracking
A hard, low-friction coating layer resists galling and cracking through roll-forming and bending — so the fabricated tray keeps its full coating, with no bare steel exposed.
Environmentally Responsible
Eliminating the post-galvanizing process reduces environmental load. Aligned with 3S's commitment to sustainable manufacturing.
GI vs. POSMAC
| Property | Standard Galvanized (GI) | POSMAC |
|---|---|---|
| Corrosion Resistance | Baseline (1×) | 5–10× |
| Formability | Prone to galling | Excellent (anti-galling) |
| Post-Galvanizing Required | Yes | No |
| Marine Environment Suitability | Moderate | Excellent |
| Environmental Load | Higher | Lower |
PosMAC Grades
POSCO sells POSMAC by magnesium content. The more magnesium in the coating, the harsher the environment it can stand.
PosMAC® 1.5
1–2% MgA fine surface finish for parts that stay dry and stay seen — automotive body panels and home appliances.
PosMAC® 3.0
≈3% MgUsed by 3SSteel structures and energy installations. Over 5× the corrosion resistance of standard galvanized steel.
PosMAC® Super
5–6% MgUsed by 3SBuilt for the environments that eat steel — high salinity, high humidity, industrial air. Twice the corrosion resistance of PosMAC 3.0.
3S specifies PosMAC 3.0 or PosMAC Super depending on where the tray will live — the salt load of the deck decides the grade.
See POSMAC in Action
The Diet Cable Tray puts POSMAC's corrosion resistance to work — non-welded, bolt-free, and up to 20% lighter.