Schmelztauchveredeltes Feinblech.Hot-dip coated sheet.

Corrosion protection
A zinc coating applied to steel in an
immersion process has for a long time
been ideal in corrosion protection.
The zinc actually protects the steel
underneath in two ways:
• First the zinc layer forms an adhering
protective jacket, which protects the
steel when subjected to weathering
(barrier effect).
• On the cut edges and those places
where this jacket sustains damage
through to the steel base, the base
zinc first dissolves in a conducting
medium (dirt, drops of water), i.e.
“is consumed”, before the steel is
attacked. This is termed the “cathodic
protective effect” of zinc.
In the cases of GALFAN ® and
GALVALUME ® the corrosion resistance
is improved by the aluminium in the
coating, so that it is possible to work
with thinner coatings. GALVALUME ®
corresponds to the corrosion protection
class III of DIN 55 928, part 8. Where
by damage or cut edges, zinc is “consumed”
over time as a result of the
cathodic protection, the aluminium in
between continues to protect the steel.
A special finish is produced by adding
an organic thin-film coating. This is
applied at a thickness of 3 – 6 µm in the
coil-coating process. It is pigmented to
guarantee weldability. This thin-coated
sheet can be formed, welded and painted
using the usual processes, though
the process parameters may have to be
adapted. The field of application is the
autobody area in the automotive industry,
where significantly improved
corrosion protection can be achieved,
especially in the flange area, when used
in accordance with the design. Secondary
corrosion protection measures
such as wax soaking, seam sealing and
the like may be unnecessary.
The corrosion protection can be significantly
enhanced by a paint coating.
If the hot-dip coated sheets are
arranged according to the most important
corrosion criteria and compared to
cold-rolled steel, the results are:
Kriterium Feuerverzinkt Galvannealed GALFAN ® GALVALUME ® Feueraluminiert Kaltfeinblech
Criterion Hot-dip galvanized Galvannealed GALFAN ® GALVALUME ® Hot-dip aluminized Cold-rolled sheet
Korrosionsbeständigkeit,
unlackiert
gut – verbessert hervorragend hervorragend –
Corrosion resistance
unpainted
good – improved excellent excellent –
Lackierbarkeit (KTL) gut zufrieden stellend gut – – hervorragend
Paintability (KTL) good satisfactory good – – excellent
Korrosionsbeständigkeit,
lackiert (KTL)
gut hervorragend gut – – noch gut
Corrosion resistance
painted (KTL)
good excellent good – – still good
Phosphatierbarkeit gut hervorragend zufrieden stellend – – hervorragend
Phosphateability good excellent satisfactory – – excellent
Kraftstoffbeständigkeit zufrieden stellend – zufrieden stellend – hervorragend unzureichend
Fuel stability satisfactory – satisfactory – excellent inadequate
KTL = Kathodische Tauchlackierung/Cathodic painting
21