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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.

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.

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.

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.

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.

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.

The increasing use of aluminum for engine and cooling system component design has resulted in the need for improved monitoring of cooling system performance. These new systems are more susceptible to damage from corrosion and overheating. A sensor is now available that responds to inhibitor depletion and to low coolant level in service. This device combines sensing electrodes and electronics into a package that mounts directly onto the radiator and provides a compatible vehicle computer output. This paper describes the design, application, and performance of this sensor.

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.

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.