Aluminium

Corrosion resistant? Hardly! It dissolves readily in weak acids, and in powdered form reacts violently with caustic soda.

http://www.coleparmer.co.uk/techinfo/ChemComp.asp

" ... and it was rusty."

Do you mean it had the characteristic rust-coloured 'lumpy bits'? If so, either it wasn't (pure) aluminium, or it was exposed to a very hostile atmosphere.

Just for a laugh, check it with a magnet.

Do you mean anodize? Do you know the specks?

It may be because of impurities in the aluminium.

Cast aluminium for example is rather impure an do not anodize well.

Could be surface contamination. Rust will sometimes form even on stainless steel if the surface is contaminated;(such as stainless castings that have been roto blasted with iron bearing pellets.

Galvanized aluminum? Galvanizing is ordinarily done for protection of steel. Aluminum alloys are typically anodized for protection.

Aluminum will corrode badly around fasteners if there is are galvanic potential difference. In ordinary usage, an oxide film forms on the surface of aluminum, and this prevents further corrosion from ordinary exposure to air and water -- the kind of thing that will cause steel to rust quickly.

'Galvanised aluminium' does not exist, as far as I know. Too exotic and not potentially very usefull. With regard to your rusted wire, its proper name has likely been misstated by someone along the supply line...

Probably what you are looking at is Aluzinc wire (Al-Zn coated steel wire), or Al-coated (steel) wire. Both will rust if exposed outdoors or long enough in very humid/ hot environments.

Just ask for the specs.

Always keep in mind that each 'corrosion resistant' material (including stainless steel and aluminium grades) is restricted to certain environments only. Think twice before selecting/ designing for outdoors, offshore etc applications. This goes double for coatings, which are thin and much more sensitive.

Best of luck

Anodized aluminium has a microscopic layer of aluminium oxide (Al2O3) covering on it, the anodized surface will give som protection against corrosion, but this surface covering is slightly porous!

To understand this you have to understand what anodizing is, it is a covering of microscopic hexagonal crystals of Al2O3, this material is virtually indestructable as it is the same as sapphire and ruby. But the boundary between each crystal is quite rough so they do not fit together exactly, this minute fissure between each crystal will allow water, air and other substances to penetrate the covering. This property is the reason that anodizing can be coloured by mettalic oxides.

If an anodized sheet of aluminium is bent or formed in any way then this will accentuate the microscopic fissures between the crystals and thus accelerating the rate of corrosion.

Spencer.

Some grades may be corrosion resistant, some are definitely not and it does most importantly depend on the grade. It will also depend on the environment it is in. Contact with different gases, liquids, solids, temperatures, humidities will all have different effects. Stresses, tension, compression, flexural and their magnitude; all have varying effects on the rate of corrosion. Aluminium has an indeterminate fatigue strength so stresses in important components under cyclical stresses must be kept low. It would be best to avoid aluminium in highly stressed components without thoroughly undertaking endurance rig tests after completing a thorough finite element analysis and understanding what is going on. However we can all point to aluminium conrods, boats and aircraft components etc that have never failed, but also to some that have!

So do plenty of research, ask questions and you will be successful, but be careful. You'll probably now tell me your application was to fence in some chickens or make some beach furniture - well - there you go.

Aluminum corrosion resistant is a sweeping statement. The corrosion aspects depend on many factors. There are various types of corrosion too. An unprotected aluminum will readily disintegrate in saline atmosphere. Pure aluminum has relatively better corrosion resistance than alloyed ones. To take advantage of many favorable characteristics of the metal several surface protection technologies like electro less conversion coating, anodic conversion, hard anodizing, cladding aluminum sheet materials with pure aluminum etc have been developed and of course most of the times these are followed by primer coat and painting.

"Aluminum" is certainly not corrosion resistant. Relatively few people have ever seen Aluminum. What you see when you look at a sheet (or flakes, granules, etc) of Al is actually aluminum oxide. This is the "resistant" surface of aluminum that tends to pretect against further oxidation, etc. This is the reason many metals are welded under an atmosphjere of argon, etc.

Take some drano crystals (NaOH) and mix it with water in a steel pot.

Put a piece of Aluminum in the pot and watch the Al corrode very rapidly.

This is a great method for removing an Al coating/galling on a steel part. Sodium Hydroxide does little damage to the steel, but just eats away at the Aluminum.

Please don't do this. Under the wrong combination of circumstances the highly exothermic reaction can become explosively fast.

Aluminum can be considered corrosion resistant in certain environments yes. That being it may deteriorate in the presence of oxygen and sunlight without a protective coating. It may deteriorate rapidly in salt air or worse in salt water, especially in the presence of heat and or agitation.