Identification of the Base Alloy
Probably the most important, and usually the first step
in the repair operation, is identifying the aluminum base
alloy being repaired. If the base alloy type is unknown, one
could contact the original manufacturer of the component
to establish the aluminum base material type. If the base
material type is not available through a reliable source, it
is impossible to select a suitable welding procedure.
There are many different types of aluminum alloys,
some have very good weldability and others have extremely
poor weldability. Unfortunately, if the base material type
is not known, or unavailable, chemical analysis is the only
one reliable way of establishing the exact type of aluminum
alloy. A small sample of the base material must be sent
to a reliable aluminum-testing laboratory, and a chemical
analysis must be performed. Generally, the chemistry can
then be evaluated and a determination as to the most
suitable filler alloy and the welding procedure can be made.
Cleaning and Material Preparation Prior to Welding
It is very important to clean the repair area completely
prior to performing the weld repair. This is typically
achieved using a degreasing solvent to remove
hydrocarbons followed by stainless steel brushing to
remove the aluminum oxide. More aggressive filing, or
chemical cleaning, may be required for some applications.
In situations where it is necessary to remove existing weld
or base material in order to conduct the repair, you need
to consider the methods available to perform this operation
as well as their effect on the finished weld. If you need to
remove a crack in the surface of a weld prior to re-welding,
you must use a method that will not contaminate the base
material to be welded. Care should be taken when using
grinding discs as some have been found to contaminate
the base material by depositing particles into the surface of
the aluminum. Routing and chipping with carbide tools is
often found to be a successful method of material removal.
Base Material Strength Reduction After Welding
There may be considerations relating to the effect of
the heating of the base material during the repair welding
process. Aluminum alloys are divided into two groups:
2. Non heat-treatable
Typically, the non heat-treatable alloys are used in a
strain-hardened condition and the heat-treatable alloys
are usually used in one heat-treated form or another.
During the welding process, the heat introduced to the
aluminum base will generally reduce the strength of the
base material in the heat-affected zone (HAZ).
Considerations When Repairing Aluminum Structures
The amount of reduction in strength and the size of the
area affected is dependent on the original condition of the
base material prior to welding and the temperature and
time at temperature of the base material during welding.
The as-welded strength, as opposed to the original base
material strength, may need to be considered after welding.
Repairing High Performance Aluminum Alloys
Another consideration associated with the repair of a
small group of aluminum structures is the temptation to
repair high performance, typically high replacement priced
components, made from specialty aluminum alloys.
These materials are often found on aircraft, hand gliders,
sporting equipment, and other types of high performance,
safety-critical equipment, and are not usually welded on
the original component. There are a small number of
high-performance aluminum alloys that are generally
recognized as being un-weldable.
There are many considerations associated with the
successful repair of aluminum alloys. Most important is
to understand the many different aluminum alloys and that
they all require indvidual consideration. The majority of the
base materials used for general structural applications can
be readily repaired using the correct welding procedure.
The majority of welded aluminum structures are designed
to be used in the as-welded condition and, therefore, with
the correct consideration, repair work of previously welded
components can be conducted satisfactorily.
Cracked repair weld due to improperly preparing the repair area.