The acidity or alkalinity in the environment above and below certain pH levels greatly affects the rate at which aluminum corrodes. Corrosion resistance is dependent on the protective oxide surface film (anodizing). Abrasions to this surface will greatly reduce the aluminum's ability to protect itself. The oxide film is self renewing under the presence of oxygen, so for corrosion to take place, conditions must be such as to continually abrade the film mechanically, or are those that locally degrade the oxide film with a limited presence of oxygen that would normally renew the film. Some cleaning agents can produce a corrosive environment to the metal, and mixed in there with grease that would inhibit the oxygen that is required for the surface film to renew itself, the corrosion you speak of will occur. The best prevention is periodic cleaning with mild soap and fresh water, and if possible, drying.
DON'T Use bleach or chlorides. They have a tendency to leach on the aluminum, which could lead to staining and pitting. Use abrasive cleaning products. Never use steel or brass wool, wire brushes, polishing wheels, rubbing or polishing compounds. These items will remove the anodizing and lead to pitting. Use concentrated alkaline base solutions, many detergents fall into this category.
Dennis Young Hotaka, Japan
> Does anybody know what causing "pitting" of alloy parts? I've noticed > this pitting on the bases of Cinelli stems, and seatposts where they > were inserted. These are typically greased fittings that are really > puzzling me. I know certain detergents that are high alkali cleaners > (high PH) are caustic to soft metals, that maybe the previous person > cleaned the bike with some kind of cleaner that was corrosive. That is > my only guess. I'm sure you've all noticed this too. Please note that > what I'm talking about is "pitting" and not the typical scratches that > take place. Anyway, I'd like to be able to prevent such pitting from > occuring in the future. Any advice would be appreciated.
> Scott Sweeney
> Salinas, CA