Question on painting

[Paul Perry (Frostwave)]

It's very possible that this aluminum either isn't aluminum at all (stainless steel), or has a lacquer finish. Untreated aluminum will oxidize over time, simply from atmospheric conditions, not necessarily from getting wet.

Well, who knows, maybe some of it was anodized.. and there is no telling really what an unmarked box is made from (I actually asked a guy making cast metal boxes and he said, "at least 70% aluminum" which gives reasonable scope). But I've been salvaging scrap since 1959 (seventh grade) so I know it wasn't stainless steel
What will accelerate alumium decay, is having dissimilar metals bolted to it, or salt spray.
If the untreated aluminum in my room is decaying, it's doing it at geological time scales.

[dacaumodo]

Now it also depends what degree of oxidation one deems acceptable. So long as it doesn't stain your fingers and clothes and doesn't get really damaged (like chips of aluminium falling off and messing with the electronics inside), and so long as, broadly speaking, it doesn't look like an unearthed WWII mine, it can be alright...

[petemoore]

  McMaster Carr has a great catalogue, and provides lots of info on different types of aluminum, from soft to very hard, and types known as 'not good' for transferring electrical currents via 'other metals' and also we bought some stuff for framing/rigging/electrical conduction [I was like...measure the conductivity and/or just strap a connection wire there...which is what we did, after buying some 'more expensive' aluminum...36 instead of 10 buxx IIRC]...\ 
  I guess Hammond and other project enclosure Mfr.s have
A Chosen the very finest materials for the appliciation.
B Took into consideration some of the 'actual use' applicationS, and chose a 'suitable' material, less expensive.
C Took whatever they knew someone had alot of they were trying to get rid of and used that.
  I'd guess [based on the rep of Hammond and Hammond boxes], the material deciders fall somewhere between B and A.
  Alot of testing was surely done...You know *I would anyway...subject prototypes to chemicals, currents, stresses, impacts etc...test for conductivity, resistance...'and' ability to be easily molded and replicated precisely enough.
  The 'other guys' probably did some 'research' or researched it and followed suit as exactly as they could or by coincidence.
  It makes sense to follow suit, perhaps Hammond guys knew somebody who has worked with and knows of [various types of] aluminums performance in various applications/
  Aluminum
A metallic chemical element, symbol Al, atomic number 13, atomic weight 26.98154, in group 13 of the periodic system. Pure aluminum is soft and lacks strength, but it can be alloyed with other elements to increase strength and impart a number of useful properties. Alloys of aluminum are light, strong, and readily formable by many metalworking processes; they can be easily joined, cast, or machined, and accept a wide variety of finishes. Because of its many desirable physical, chemical, and metallurgical properties, aluminum has become the most widely used nonferrous metal. See also Periodic table.

Aluminum is the most abundant metallic element on the Earth and Moon but is never found free in nature. The element is widely distributed in plants, and nearly all rocks, particularly igneous rocks, contain aluminum in the form of aluminum silicate minerals. When these minerals go into solution, depending upon the chemical conditions, aluminum can be precipitated out of the solution as clay minerals or aluminum hydroxides, or both. Under such conditions bauxites are formed. Bauxites serve as principal raw materials for aluminum production.

Aluminum is a silvery metal having a density of 1.56 oz/in.3 at 68°F (2.70 g/cm3 at 20°C). Naturally occurring aluminum consists of a single isotope, 2713Al. Aluminum crystallizes in the face-centered cubic structure with edge of the unit lattice cube of 4.0495 angstroms (0.40495 nanometer). Aluminum is known for its high electrical and thermal conductivities and its high reflectivity.

The electronic configuration of the element is Is22s22p63s23pl. Aluminum exhibits a valence of +3 in all compounds, with the exception of a few high-temperature monovalent and divalent gaseous species.

Aluminum is stable in air and resistant to corrosion by seawater and many aqueous solutions and other chemical agents. This is due to protection of the metal by a tough, impervious film of oxide. At a purity greater than 99.95%, aluminum resists attack by most acids but dissolves in aqua regia. Its oxide film dissolves in alkaline solutions, and corrosion is rapid.

Aluminum is amphoteric and can react with mineral acids to form soluble salts and to evolve hydrogen.

Molten aluminum can react explosively with water. The molten metal should not be allowed to contact damp tools or containers.

At high temperatures aluminum reduces many compounds containing oxygen, particularly metal oxides. These reactions are used in the manufacture of certain metals and alloys.

Applications in building and construction represent the largest single market of the aluminum industry. Millions of homes use aluminum doors, siding, windows, screening, and down-spouts and gutters. Aluminum is also a major industrial building product. Transportation is the second largest market. Many commercial and military aircraft have become virtually all-aluminum. In automobiles, aluminum is apparent in interior and exterior trim, grilles, wheels, air conditioners, automatic transmissions, and some radiators, engine blocks, and body panels. Aluminum is also found in rapid-transit car bodies, rail cars, forged truck wheels, cargo containers, and in highway signs, divider rails, and lighting standards. In aerospace, aluminum is found in aircraft engines, frames, skins, landing gear, and interiors, often making up 80% of a plane's weight. The food packaging industry is a fast-growing market.

In electrical applications, aluminum wire and cable are major products. Aluminum appears in the home as cooking utensils, cooking foil, hardware, tools, portable appliances, air conditioners, freezers, and refrigerators, and in sporting equipment such as skis, ball bats, and tennis rackets.

There are hundreds of chemical uses of aluminum and aluminum compounds. Aluminum powder is used in paints, rocket fuels, and explosives, and as a chemical reductant.
  http://www.answers.com/aluminum?gwp=11&ver=2.0.0.453&method=3

[ildar]

What comes to question then is the purity of the aluminum. Often other metals are mixed to aid in casting and tooling, so I would assume that what we may take for granted as being "aluminum" isn't pure, or pure enough.

[Meanderthal]

Yes, I've heard that the die-cast enclosures we use are actually aluminum+zinc+silicon dioxide(sand)+other stuff... just a rumor... I don't know how factual this is. The guy who told me this called it "white metal", but the junk white metal I've seen other than this is much weaker, so I took that with a grain of salt.