Alnico is often said to have excellent corrosion resistance. The corrosion resistance offered actually depends on the grade of Alnico and the chemicals it is exposed to. Alnico does contain some free iron so it may be prone to surface corrosion with water. But it is excellent for corrosion resistance when used in motor oil, organic solvents, petrol and alcohol. It offers a degree of corrosion resistance to dilute organic acids and hydrogen peroxide. It will show signs of corrosion over time when exposed to salt water, strong alkali solution and inorganic acids. It is possible to put a protective layer over the alnico e.g. Ni, Zn, paint, etc.
Although not always regarded as necessary, the Alnico magnets are sometimes given a protective coating or even simply a coating to make the magnet more aesthetically pleasing. The colour of the coating is almost always red. This is why Alnico magnets are often known as Red Magnets by many people (although ferrite magnets are also sometimes coloured red in pot magnet assemblies and are also known as red magnets). Other colours can be used to colour the Alnico (e.g. black).