Corrosion Resistant Bicycle: Parts

Video Transcript

Charles McMahon for Expert Village. We are talking about how bicycles are put together and the materials. If you want more information you an look at a college level text book, on merionmedia.com. Obviously you are using a bike out of doors in all weather, so the components have to resist corrosion. While the rims are made from a high strength aluminum alloy, actually by an extrusion, extruded through a die, it has got a very funny cross section, so it is an aluminum alloy, the spokes are normally stainless steel although you can get carbon steel spokes. Now the aluminum doesn’t corrode, no aluminum doesn’t rust, the reason is it has a very thin oxide layer, so thin you see through it, so what you see is the aluminum underneath. But this oxide layer is so complete and tenacious that it separates the aluminum metal from the oxygen in the air and the water vapor and so on. So that’s why aluminum doesn’t corrode. It is passivated by this oxide. The stainless spokes don’t corrode, because they have enough chromium atoms mixing with the iron to form an oxide that is chromium rich. And that oxide acts the same as the aluminum oxide it passivities the stainless steel with this chromium rich oxide and therefore the metal underneath can’t rust. So they both have the same principles in both cases. Both passivated the rim by aluminum oxide and the stainless steel spokes by a chromium rich oxide, the hub is normally also aluminum Now the reason you like aluminum out here is obviously it is lighter. So you would rather have aluminum than steel out here. If you use steel, you probably use chromium-plated steel and that will last for while, but the chromium plating gets pits and then you can get corrosion in the pits. You can use carbon steel spokes, they have to be coated with either zinc or cadmium a sacrificial layer, as long as that layer is on that will protect them but when that layer is gone they will rust. So best is aluminum rims, stainless steel spokes.

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