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Exterior automotive trim materials are exposed to aggressive environments and therefore must have satisfactory corrosion resistance. Stainless steel materials such as bimetal (stainless steel clad aluminum) are therefore used extensively in this application. This paper addresses the effect of surface contamination on the corrosion behavior of stainless steels which have been fabricated with the application of a PVC polyfilm protector. The effect of residual deposits on the stainless steel has been investigated using CASS and cyclic immersion corrosion tests, Auger analysis, and gas chromatography coupled with Fourier Transform Infrared Analysis (FTIR). The mechanism of reduced corrosion resistance attributed to these residual deposits is described.

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.

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.

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.

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.

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 corrosivity of the automotive environment has become more severe in recent years due to increased use of road salts and acid precipitation. Corrosion problems associated with exterior automotive trim include I 1) effect of the trim on the auto-body steel and, 2) corrosion of the trim material itself. In addition to the corrosivity of the automotive environment, factors which cause these problems for a given material include the inherent crevice geometry, attachment requirements and susceptibility to paint damage in this area. Corrosion performance of an exterior trim depends heavily on the material choice.

The comparative corrosion behavior of noble metal coatings prepared by roll bonding (cladding) and electrodeposition is discussed in this paper. Advantages and disadvantages of these materials are listed in order to show where one materials system is preferable in a specific application. In addition to the mechanisms of corrosion, examples are described and test results are shown to demonstrate the differences in behavior of clad metal and electrodeposited materials.

The interaction of our natural elements such as rain, snow and humidity, with chemicals introduced to the environment, provides a complex chemistry which is one of the most corrosive in North America. The chemistry of this environment and its relevancy to automotive corrosion, forms the basis of this paper. An understanding of this chemistry is necessary in order to conduct meaningful corrosion tests and reduce degradation of automobiles.

This paper deals with the corrosion behavior of various exterior automotive trim materials including electroplated steel, stainless steel, stainless clad aluminum and anodized aluminum. The mechanisms of corrosion are discussed, particularly with regard to external appearance and galvanic corrosion of painted auto-body steel adjacent to the trim. Field tests on the various trim materials are described including six year service performance with stainless clad aluminum. Quality control tests for these materials which are currently utilized are listed and described.

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.

The choice of material for a particular application depends on many factors, including cost, availability, appearance, strength, fabricability, and corrosion resistance. Frequently, use of a monolithic metal is compromised by one or more of its properties. The metallurgical materials systems concept provides a means of designing specific properties into a single composite material. Two or more metals are bonded at the atomic level to form a clad metal that meets the precise requirements of a specific application. In this report technical factors involved in designing corrosion-resistance materials systems are considered. Advantages and limitations are discussed and specific automotive engineering applications are used.

A new clad metal system has been developed as a material for hydraulic brake line tubing. The material consists of a 1008 LCS/304 SS/1008 LCS composite in the ratio 45%/10%/45%. Laboratory experimental tests, accelerated life tests, and field tests were performed on brake tubing formed from this material. The results show that the brazed and ternecoat low-carbon steel/stainless steel/low-carbon steel tubing has excellent corrosion resistance and high mechanical strength. The results are compared with those obtained with conventional brazed and ternecoat LCS brake tubing.