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20

Technical Services

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:

1. Heat-treatable

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.

Summary

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.