Welding
MIC6
®
components can be successfully welded utilising the fusion based Gas Metal Arc
Welding (GMAW or Mig), Gas Tungsten Arc Welding (GTAW or Tig) and solid state based
Friction Stir Welding (FSW) processes. GMAW is used most often and GTAW has some limited
applications. Argon, Helium or a mixture of the two are the only recommended shielding gases for
welding MIC6
®
.
Because MIC6
®
has a high thermal conductivity, it is recommended to be welded ‘hot and fast’, meaning
the welding current should be set at a level that provides adequate heat input while maintaining a
moderate welding speed. Specific parameters can be found in welding handbooks such as ‘Welding
Aluminium - Theory and Practice’ from The Aluminium Association.
Aluminium filler alloys 4043, 4145 and 5356 are all acceptable for use when welding MIC6
®
. Filler alloy
4145 (10% Si, 4% Cu) offers the best weld ability and freedom from cracking with 4043 (5% Si) being a
good second choice - both would be recommended if the service temperature of the welded assembly
is above 150°F (66°C). Under some conditions (e.g. high parts restraint), filler alloy 5356 may cause some
cracking in the Fusion Zone and Heat Affected Zone (HAZ) of MIC6
®
parts. In addition, the welds
deposited with this filler alloy can be sensitised to stress corrosion cracking at high temperatures and
should be used only in service applications below 150°F (66°C). When testing under tension traverse to
the welds, 0.5 in. thick weldments, produced with the 4145 and 5356 filler wires, generally break in the
HAZ with joint efficiencies that can be as high as 96%.
In general, it is recommended to weld the MIC6
®
at interpass temperatures not exceeding 150°F (66°C).
If a pre-heat is required, the temperature should be limited to 250°F (120°C).
SURFACE PREPARATION
Pre-weld cleaning and oxide removal are important to the successful welding of MIC6
®
. Residual
machining lubricants and moisture will produce porosity in welds.
Prior to welding, solvent clean and dry the areas to be welded of surface contaminants. Aluminium’s
natural oxide melts at 3700°F (2035°C) while aluminium melts at approximately 1200°F (650°C). This oxide
can act as a barrier to adequate fusion between the weld and base metal. Usually a light brushing with a
clean stainless steel brush, after the surface has been cleaned of contaminants, will remove the oxide film.
For applications where fillet welds are used, no weld joint edge preparation is necessary. For butt joint
applications, weld joint edge preparation is required, such as a single V or double V bevel (depending
on the thickness being welded).
As with all welded assemblies, it is strongly recommended that the welding procedure used be tested
and qualified on joint mockup(s) prior to introduction and in-service use.
Painting
MIC6
®
can be either painted or powder coated. The plate surfaces should be cleaned to remove any
residual machining lubricant or oil - both water-based and solvent-based cleaners have proven effective.
Once cleaned, there are several different approaches to further surface preparation.
A chemical conversion coating in combination with a primer coat has shown to provide the best surface
protection and resistance to abrasion. In some applications, primer coats have been applied directly to
the plate surface - in other cases, even the primer coat has been omitted. A light anodise has also been
used on a limited basis for surface preparation prior to a coating application.
A surface that is free of moisture is the key to success with any coating method. Unless the surface is dry,
entrapped moisture from micro shrinkage could contribute to flaws in the final coating.
19
Aluminium Plate MIC6
®
- PRECISION MACHINED CAST ALUMINIUM PLATE
