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Technical Paper

Applications for Clad Metals in the Automotive Industry

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.
Technical Paper

The Properties of Bright Stainless Steel Clad to Aluminum for Class 8 Truck Bumper Applications

Previous work has shown that mirror bright stainless steel clad to lightweight aluminum offers an optimum combination of weight, appearance, fabricability, styling, and durability against road damage and corrosion for automotive trim and bumper applications. This paper characterizes the properties of stainless steel-aluminum clad bumper materials for application on Class 8 trucks. The rule of mixtures is confirmed for an SAE 30301 stainless steel clad to 3003 aluminum, and is applied to show the tradeoffs between weight, strength, and cost that affect material selection for truck bumpers. The fabricability is demonstrated by sweeping, aerodynamic bumper designs that are readily formed, and is quantified by forming limit diagrams of 301SS / 3003Al clad and 301 stainless steel. The durability against road damage is demonstrated with Gravelometer testing, followed by ASTM standardized corrosion testing. The clad is also resistant to erosion from water impingement.
Technical Paper

Joining Aluminum to Steel with Transition Material

1006 steel clad aluminum has been used as a transition material to directly spot weld steel to aluminum. Advantages of the clad metal transition include the ability to spot weld with existing equipment and reduction of dissimilar metal crevice corrosion at the steel-aluminum interface. Sheet steel between 0.8mm and 2.0mm has been spot welded to aluminum between 0.8mm and 3.0mm in a variety of combinations with the transition material. This paper contains specific spot welding parameters for a variety of joints containing steel and aluminum at thicknesses normally encountered in body applications. The mechanism of weld nugget formation for aluminum-transition-steel joints is evaluated. Weld lobes established according to SAE and Aluminum Association guidelines are presented. The effect of electrode design on joint strength and heat balance are discussed.
Technical Paper

Corrosion Resistance of Aluminum-Transition-Steel Joints for Automobiles

Transition materials consisting of steel clad aluminum have been used to join aluminum and steel. This technique allows joining by resistance spot welding since the clad transition material allows the actual transition from one metal to the other to occur at the clad bond interface. Welding studies show that in the recommended range of weld parameters, high strength joints are produced. A wide range of corrosion tests have been used to determine the durability of these joints in automotive environments. Results show that the use of transition material in joining aluminum to steel or EG steel eliminates galvanic corrosion.
Technical Paper

Galvanic Corrosion Behavior of Copper and Stainless Steel in Heat Exchanger Environments

Vehicle heat exchangers are exposed to a number of aqueous environments ranging from inhibited coolants to seawater. Frequently, the design of the heat exchanger results in a galvanic couple between copper and a stainless steel. This couple can either prevent or promote pitting and crevice corrosion of the stainless steel member. This paper demonstrates the use of electrochemical corrosion measurement techniques to predict this behavior. Stainless steels which have acceptable, marginal and unacceptable resistance to localized corrosion when coupled to copper in aggressive environments are described. Potentiodynamic polarization curves for a variety of stainless steels were measured in artificial seawater to determine their pitting and critical protection potentials. Mixed potential measurements for these alloys galvanically coupled to copper were then made to predict the localized corrosion behavior of the stainless steel.
Technical Paper

Transition Materials for Automotive Applications

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.
Technical Paper

The Development of Clad Metals for Light Vehicle Bumper Systems

A number of factors are considered important when considering the choice of material for light vehicle bumpers. These include economics, styling, appearance, fabricability, and durability. Additional factors are introduced due to safety, fuel efficiency and environmental issues. As these issues become more stringent, the choice of material becomes more difficult because traditional materials are not able to provide all of the required properties. This paper describes clad materials systems which provide the required properties while introducing weight reduction in bumpers. Specific combinations of stainless steel and aluminum in a clad configuration have been used on automobiles and trucks for many years in a wide range of applications. These clad metal systems have all of the desirable properties of the individual components and provide a light weight alternative to the limitations of traditional materials.
Technical Paper

Development of Coating Systems for Stainless Steel and Stainless Steel Clad Aluminum Automotive Trim

Stainless steel and stainless steel clad aluminum (bimetal) have been used for bright exterior trim for many years. The need to manufacture bright or colored trim with the same tools has led to the development of various coating systems to color stainless steel or bimetal trim. This paper describes the mechanisms of coatings disbondment that can occur on trim. Accelerated tests for determining disbondment resistance are described and the results from these tests for a wide range of coatings are presented. Coating systems that are acceptable for stainless steel and stainless steel clad aluminum are identified.
Technical Paper

Field Evaluation of the Corrosion Behavior of Bumpers

In order to confirm the behavior of various bumper materials, Texas Instruments conducted a performance field survey of existing bumpers in service. A large fleet of trucks equipped with stainless steel clad aluminum bumpers was identified in order to maximize the data obtained on this material system. The fleet owned and operated by E. W. Wiley Co., Fargo, North Dakota was chosen because of the large number of accessible bumpers in service, the severity of the location and the extensive service of trucks in that fleet. Bumper system included in the survey were stainless steel clad aluminum, chrome plated steel and chrome plated aluminum.
Technical Paper

Development of PVC Coextruded onto Stainless Steel Clad Aluminum Trim

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.
Technical Paper

Joining Dissimilar Metals With Transition Materials

Galvanic corrosion and mechanical properties are major design considerations for bimetallic assemblies. Galvanic corrosion can lead to rapid degradation while welding of dissimilar metals such as steel and aluminum can lead to reduced structural stability. This paper describes a new concept in joining dissimilar metals involving the use of transition materials. The clad transition materials is composed of the dissimilar metals to be joined and effectively reduces the corrosion and mechanical problems associated with the system. Results of galvanic corrosion field tests and welding studies for transition materials are presented and several examples of automotive applications are cited.