The so-called rust is relatively speaking. If LZ defines rust as red-brown rust spots similar to rust, aluminum-magnesium alloy will not be like this. However, if rust is defined as the material being oxidized, aluminum-magnesium alloy The alloy is easily oxidized. If the environment is dark and humid, the result will be more serious and many white spots will appear on the surface.
So depending on the specific material and situation, appropriate surface treatment is generally required, such as phosphating, spraying, polishing, gold polishing, etc.
As for outdoor billboards, this still depends on the specific situation. If handled properly, it can be used for five or even ten years.
I hope the answer will be helpful to LZ.