Simple Aluminium Treatment For uncoated one thousand series alloys

Simple Aluminium Treatment For uncoated one thousand series alloys.

just a comment – this treatment scheme does not include any notion that the surface is anything other than a simple oxide coating. Our clad surfaces anodising and chromate conversion coatings are not covered in this outline.
Birmabright is a common 1000 series alloy that uses up to 5% magnesium and manganese. This ally was introduced by the berm it group in 1929 and was noted for its corrosion resistance it was used extensively in light alloy boats. The constituents were 1 to 7% magnesium with less than 1% manganese the remainder was aluminium. The Allies were provided in different temper conditions e.g. soft quarter hard half hard and were designed to be work hardened by cold pressing into shape. Weldability was good but machineability was poor.
Burma bright was used extensively in Land Rover and other classic vehicles from the early 30s. It was used for the bodywork of the thunderbolt land speed record car and also for Bluebird. Strengthening ribs in the DB18 Daimler were made of this alloy.

Dust is one of the major causes of deterioration of the surface of aluminium in museums. Aluminium in storage in a dusty environment will show pitting and accretions on the surface quite quickly. If you look at the aluminium pool bay diagram you will realise that acid and alkali are both harmful to aluminium and cause a breakdown of passivity. If the environment has a dust that absorbs moisture such as superphosphate or chlorides from the sea then the deterioration will be far quicker. The deterioration will continue even if the relative humidity is reduced to quite low levels.
Impurities from the atmosphere and also from the alloy itself will form into inter-metallic species that will promote “bimetallic corrosion” on the surface of the alloy itself. Re-establishment of the passivity of the surface is essential for the preservation of the aluminium alloy object. This has to remove the into metallic species from the surface and re-establish a compact oxide film.

We should not be afraid of making decisions that may seem quite interventive this is what may be required. A preventive conservation approach is not going to work with the conservation of light alloy objects unless you live in a total desert.

Intervention is necessary.

Two passivate the surface we need to;

• Remove dust and accretions.
• Remove metallic oxides.
• Remove into metallic species from the surface.
• Passive fate the surface.
• Re-establish the surface a aesthetic.

Possible treatments are;

• Immersion in neutral ammonium sulphate.
• immersion in neutral ammonium citrate.
• Treatment with organic acids such as citric acid.
• Treatment with mineral acids such as phosphoric, chromic, nitric, sulphuric, hydrofluoric.
• Treatment with inhibited alkali washers.
• Detergent washes.
• Combinations of the above.

Note I haven’t included in the electrochemical methods.

Removal of dust and accretions can be done with detergents and nonmetallic (nylon) scrubbing brushes. Removal of metallic oxides and into metallic species from the surface can be done with complexing agents or mild acids.
Passivation of the surface can be done with mineral assets of the phosphate or chromate type.
Re-establishment of the surface aesthetic can be done with the original kind of surface preparation used on the object. This obviously has to be done with some judgement.
With aluminium the surface finish can either be chemical chrome eating phosphate in anodising mechanical so that scratch brushing and things like that or a paint system.