We have designed and manufactured a structure that comprises extrusions and plate in aluminium alloy 2014A. We are seeing significant, and unacceptable, atmospheric corrosion on the structures after a relatively short service time. What are our options?

Presumably you selected 2014A because of its high mechanical properties but were not aware that all of the 2000 series alloys, which are based on aluminium copper, have relatively poor atmospheric corrosion resistance.

There are a number of possible ways ahead, but all will require some thought and re-design of your structure.

Firstly we have to ask, "do you really need the mechanical properties of 2014A?" If the answer is yes then the following options are open to you.

It is possible, during the manufacture of plate and extrusions, to clad the 2014A with a skin of pure, or commercially pure, aluminium that is metallurgically bonded to the core alloy. Thus we have a composite of a strong core with a corrosion resistant skin.

This is good but remember that:

• the section will probably need to be made thicker as the pure aluminium part of the cross section is much weaker than the core.
• a cut cross section that exposes the core to the environment will be a site for corrosion, such edges must be protected.
• these materials will probably incur price penalties, the extrusions may have to be "custom made".

If the design can be modified to significantly increase section thickness then you should consider changing to an alloy from the 6000 series, such as 6082. This alloy has appropriate corrosion properties but has a 0.2% proof stress, in the T6 condition, only about 66% of 2014A in the T6 condition.

6082 has even better corrosion properties in the T4 (naturally aged rather than artificially aged) condition but the 0.2% proof stress is only about 50% of 2014A.

The 6000 series alloys are at least as formable and machinable as 2014A and generally are easier to join by the usual welding and brazing processes.

Presumably you have incorporated protective anodising into your current design. If not then, dependent upon the extent of your corrosion problems, this, alone, may be a satisfactory solution.

If protective anodising alone is not adequate then you could consider some form of additional paint or powder coating.

Another, newer, process that may be a solution is the Keronite process. This is a plasma enhanced oxidation of the surface that gives a different type of film to anodising that can be very protective.

All of these options require some redesign, probable changes in manufacturing routes and processes and costs. You will need to consider all of these points to select the optimum solution.

Further information

Corrosion Committee

Light Metals Division