Surface World December 2019 Surface World December 2019 | Page 28
QUALICOAT UK & IRELAND
The ‘Coatability’ of Aluminium
Architectural powder
coating has generally been
seen as an impervious
coating on aluminium,
one that will cover any
imperfection present
on the aluminium surface.
In reality however powder
coating is permeable; it is
the job of the aluminium
pretreatment system
to offer the impervious
fi nish to the aluminium
whilst offering the ‘key’
for good powder coating
adhesion. Furthermore the
quality of the aluminium
alloy and surface fi nish
prior to pretreatment is
crucial to gaining good
life expectancy of the
completed fi nish.
As a specifier, the choice of aluminium
grades and suitability for the application
is important to consider, not only for the
structural capability of the installation, but
also the life expectancy of the finish which
often determines the life of the installation.
QUALICOAT has actively been researching
this area for some time to assist specifiers in
getting the best quality architectural coatings
through QUALICOAT licensed, third party
accredited supply chains.
Contrary to popular belief powder coating
cannot be used to hide poor or corroded
aluminium profiles. Very lightly oxidised
aluminium, unseen to the naked eye,
can be powder coated successfully as the
pretreatment process removes the natural
oxidisation. It is important to note that
as soon as unfinished aluminium is in
contact with oxygen then oxidisation begins.
The importance of using ‘fresh’ mill material,
kept in a temperature controlled store, will
help reduce oxidisation, as will aluminium
surface protection and the handling of
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unfinished aluminium with gloves. Where
visible oxidisation appears on an extrusion,
generally as a white substance, it becomes
unsuitable for powder coating. Where
this surface oxidisation is present, it is
the responsibility of the powder coater to
advise their client that their material cannot
be coated.
As the level of recycled aluminium content
continues to increase there is a need to
monitor the quality of the aluminium billet
itself, whilst extrudable, the possible increase
in contaminants within the aluminium may
reduce the performance of the coating.
QUALICOAT have undertaken research
in this field over the last few years and have
produced a document which explains
what the acceptable tolerances should be.
‘Recommendations for Aluminium Alloys’,
which is available on the QUALICOAT UK
& Ireland website, explains in more detail
the recommended tolerances.
Aluminium ‘6000’ series extrusion grades
EN AW 6060 and EN AW 6063 are
commonly used for architectural aluminium
systems. These grades allow for various
alloys to be present,
however, QUALICOAT
research suggested that
these alloys should be a
little tighter specified and
if they are, the life
expectancy of the coating
would be increased.
monitoring and handling when it comes
to longevity of powder coat finishing.
QUALICOAT is the only powder coating
association that is undertaking pioneering
research into not only the ‘coatability’ of
aluminium extrusion, but the coatability of
aluminium sheet and aluminium castings.
This research sets the standards to which
others follow.
Copies of the new sixteenth edition of
the QUALICOAT Standard, is available
through the UK Association website,
www.qualicoatuki.org together with
an up-to-date list of approved Powder
Suppliers, approved Pretreatment
Suppliers and licensed Applicators.
Printed literature and telephone
support is available from QUALICOAT
UK & Ireland Head Offi ce in
Birmingham on 0330 236 2800 or
email [email protected].
The Association can also be followed
on Twitter @Qualicoatuki
It is also noted that
inappropriate tempering
or hardening of the
aluminium extrusions
to increase its structural
strength, normally to the
T5 or T6 grades, can
cause structures to
form in the aluminium
surface which are more
susceptible to corrosion.
QUALICOAT’s research
shows that by monitoring
the hardness level within
prescribed values, by the
‘Best Webster’ or ‘Brinell’
hardness method, life
expectancy can again
be extended.
It is worth noting that
aluminium ‘5000’ series
sheet grades also benefit
from similar material
DECEMBER 2019
twitter: @surfaceworldmag