A method for forming a protective coating containing aluminum on the surface of a metal part, wherein the part is contacted with a carburizer made of an aluminum alloy, at a treatment temperature and in a chamber, the atmosphere of which contains an active gas which reacts with the carburizer to form a gaseous aluminum halide, which decomposes upon contacting the part while depositing aluminum metal thereon. In the method the aluminum alloy of the carburizer includes at least one element, zirconium and/or hafnium, the active gas reacting with the carburizer to also form a halide of the reactive element which decomposes upon contacting the part while depositing the element thereon at the same time as the aluminum.