Diffusion alloying of thin stainless steel foils by simultaneous addition of Al and reactive elements

Automotive catalytic converter lifetime is linked to the amount of aluminum present in the base alloy that promotes the formation of a protective alumina layer. The process involving cold rolling and annealing of Al-steel-Al sandwiches allows to produce an alloy containing more than 7 wt.% of Al. Unfortunately many α-Al2O3 scales tend to spall particularly during thermal cycling with consequent revelation of the bare alloy. Small additions to the ferritic stainless steel of oxygen reactive elements are known to improve the adhesion of α-Al2O 3 scales. In this work yttrium was added to the aluminum foil before roll bonding and its behavior during the diffusion bonding was evaluated. This novel process, that appears really promising, allows to overcome problems related to steel alloying with reactive elements and reduces the quantity of expensive reactive elements that needs to be added per square meter of catalyst carrying foil.