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Transition materials which are used to join dissimilar metals such as steel and aluminum on automobiles are described in this paper. The problems associated with conventional methods of joining these two metals include galvanic corrosion, brittle welds, reduced mechanical properties and reduced design flexibility. These problems are solved through the use of clad transition materials at the joints. Transition materials are fabricated by roll bonding dissimilar metals to form the clad materials and subsequently forming the materials to the desired configurations. The clad material allows the actual transition from one metal to the other to occur at the clad bond interface and thus only similar metal joints exist in the assembly. Welding studies describe the high strength and ductility of steel to aluminum joints through the use of steel clad aluminum transition materials.

Stainless steel clad aluminum has been used for exterior automotive trim for many years because of its unique bright, corrosion resistant properties. Recent styling trends have led to the use of black plastic to partially cover the stainless steel surface providing a “black on bright” trim system. The most economical process for manufacture of these systems is coextrusion of PVC onto bimetal during the roll forming process. This paper describes the process for manufacture of stainless steel clad aluminum and for coextrusion of PVC onto the bimetal. Important process steps which are covered include roll bond preparation, roll bonding, buffing, coextrusion preparation, surface treatment, adhesive application and coextrusion.

Clad metals are metallurgical materials systems comprised of two or more metals or alloys which are metallurgically bonded to form a single material. This results in specific and unique properties of the clad metal system which are not available in a monolithic metal or alloy. Historically, they have been used for many decades by the automotive industry but the cladding process as well as the ability to design specific properties into a clad system are not well understood. This paper describes the cold roll bonding process for fabrication of clad metals. The mechanism of bond formation and limitations of the process are discussed. Rules for calculating a number of properties of clad metals are presented. Methods for designing clad metals to obtain unique properties for specific applications are described. The history of the use of clad metals on automobiles is also reviewed.