The basic principle of passivation of aluminum is that strong oxidizing acids such as cold concentrated nitric acid, concentrated sulfuric acid, etc. encounter aluminum, instantly produce a dense oxide film on the surface of aluminum, thereby preventing further reaction of aluminum and strong oxidizing acid.
Others such as iron can also undergo passivation.
The passivation reaction equation of aluminum is: 2Al 6HNO3(concentration)=Al2O3 6NO2 3H2O, 2Al 3H2SO4(concentration)=Al2O3 3SO2 3H2O, the essence of passivation is to generate a dense oxide film.
The phenomenon of forming a dense oxide protective layer on the surface of aluminum and other metals to prevent further reaction with the metal is called passivation.