Most aluminum products are clear coated or anodized to prevent oxidation. i.e. Rowland as an example. If you look at a car aluminum wheel, the are all anodized.
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Aluminum reacts with oxygen to form aluminum oxide. This oxide will completely cover the surface between the raw aluminum and the atmosphere and prevent any additional reaction with oxygen. The layer formed is about 3 to 4 nanometers in thickness. The process of anodizing aluminum actually increases the thickness of this layer and makes it harder.
Far more manufacturers using aluminium chasis. Most of heatsinks are aluminium. The lifespan of aluminium chassis is far larger than human lifespan so nothing and nothing to scratch your head about in any case. Raw aluminium can be toxic if digested so it's not recommended to cook a food on untreated aluminium. Other than that there's no toxines getting airborn off the aluminiumn surface.
Raw aluminum in salt air, (tropical island, coastal areas) will corrode and be damaged. it will continue to get worse.
IE it does not form a thin layer, but more like rust on iron, continues to penetrate the surface to depth.
Anodizing helps, and for most environments will prevent corrosion. However in a very salty air humid environment the corrosion will still take place eventually unless the surface is kept polished with a coating of wax.
In most non-salt air places, the corrosion forms only a thin layer and stops.
Aluminum wheels in Northern areas where salt is placed on the road suffer the same, unless covered with a good layer of clearcoat.
I live and work near the Pacific Ocean. Aluminum even NEAR the ocean will turn to a powdery dust if left untreated. I remember as a child we would have to replaice our aluminum patio furniture every year as it would weaken and become unsafe. I worked for the Telephone company and in coastal zones we used copper or stainless steel in lieu of aluminum to stop the disinitegration of our outside plant infrastructure.
I would be concerned if I lived very close to a beach with salt spray present in the air. Absent salt spray, Drrsutlif's comments are accurate. As far as aluminium and alzheimer's disease, that arose from a finding that amyloid plaque contains elevated levels of aluminum. Current thinking is that this is a coincidental not a causual relationship.
First response is the one that makes practical sense. Would any of you have sympathy for or buy anything from a neglectful lazy pig who after spending good money on gear lets it rot, never paying attention to it's appearance? My goodness! Wipe it off with a damp cloth once in a while, dust it off, don't use it as a coffee table and spill beer on it. Take the same care as anyone anywhere and it'll still look great 20 years later.
Caveat: don't forget to take the lid off and blow it out with compressed air too.
As mentioned Drrsutliff, the surface of aluminum oxidizes to create a coating of aluminum oxide. This surface adheres strongly to the aluminum and protects the unoxidized aluminum beneath it. Steel, as we know also oxidizes, however this creates rust which progressively falls away from the metal beneath thus allowing the oxidation to spread.
If aluminum comes into contact with salts or caustics it will cause the oxidizes to go on and spread like rust on steel.
Anodization of aluminum thickens the hard oxide layer and increases the protection against corrosion. This is generally sufficient for most applications.
I live in Quebec. We are not close to the sea but during winter the cities spread copious amounts of salt on our roads. IME The salt seems to have little impact on aluminum wheels. Mind you, I remove my al wheels and replace them with old rusty steel rims. Many other car parts are also made of al such as engine blocks and heat exchangers. I have never heard of them failing due to corrosion.
All this to say, that for audio applications I would not be the least bit worried with use of aluminum. The question is are there other materials, for audio applications, that will perform better such as carbon fibre or Kevlar?
Formerly, I worked for a leading aluminum producer.
As for toxicity, aluminum is not toxic and eating from it is in no way dangerous. Good luck not eating food that is or was in contact with al. Think al foil.
As for the link with Alzheimer's, my understanding is that al is found in the brains of patients but that arrives their "naturally" and is not a result of exposure.
There is little chance that any aluminium used in commercial audio products is in its 'raw' state.....ie...unprotected.
At the very least, a chromate coating is the cheapest but anodising is generally the most economically available product and is available in a range of colors and thicknesses (the thicker the coating...say 25 microns...gives added protection).
Powder coating of aluminium is generally cheaper than anodizing these days and is available in hundreds of colours compared to the limited range with adodising.
Powder coating provides greater protection against the corrosion of salt being a paint sealant rather than a chemical deposit as in anodising.
Anodised aluminium WILL be eaten away by salt near a marine environment and even with powder coating......any weakness in joints, edges, drilled fixing holes etc will be attacked thus making any form of aluminium in a marine environment very risky.
Two-pack polyurethane is another protective coating which can be used over aluminium but stainless steel, zinc, copper and even galvanized steel are preferable for coastal environments.
Heat and humidity in themselves will not affect any commercially protected aluminium products.
I've seen aluminum body work on cars corrode away exactly like rusty steel. The probable reason you don't see it to that extent on wheels is because they are made with alloys of aluminum, not pure. Same goes for audio component cases, I would think for the sake of durability. Although certain types of racing wheels are typically pure aluminum/magnesium.