December 2, 2021
For aluminum we use the word OXIDIZATION not RUST because only iron and steel can occur rust (which contains iron). According to Aluminum Association, " nearly 75% of all aluminum ever produced is still in use today." This shows how aluminum's extraordinary material characteristic and recyclability.
All raw aluminum we see is naturally protected by a thin layer of oxidized surface which protects the aluminum from oxygen which cause may further corrosion. The moment aluminum is exposed to oxygen oxidized aluminum is formed, it is this oxidized layer protecting aluminum from harmful environmental elements.
Photo below shows the under body power train of Tesla Model 3 which is perfect demonstration of oxidized area. My guess is because this power train is completely covered in plastic and underneath the car which accumulates water and moisture, and EV's doesn't have engine heat to remove the moisture hence caused oxidized aluminum. This white powdery oxidization is a more long term corrosion however it can easily be removed by brass or even teeth brush. For most consumers they may not notice or understand this powdery form and mistakenly think is just dirt. And 99% of the consumers will never see it nor access to it, so industrial application for castings are usually not trimmed, sanded, or grinded for sharp edges.
This oxidization is actually harmless unlike RUST that will completely decompose the material. This is why OLD aluminum castings can still be seen and exists in our daily life. And even better is it can be sanded and polished to restore to it's glory~
However, for OEM Aluminum Die-Casting company like us this kind of finish is rarely possible...all our castings are requested to be free of flash, sharp edge and all tooling heat check marks must be removed. And furthermore all castings need surface treatment for protection. This varies from E.D, solvent, powder coating, anodize, alodine etc...AGAIN, the biggest cost of the Die-Casting is the surface requirement.