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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

Corrosion Mechanisms in Bright Stainless Steel Trim Systems

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.
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

Applications of Clad Metals in Brazed Heat Exchangers

Design, fabricability, thermal, mechanical, physical and durability properties are all important to the successful application of materials systems to heat exchangers. In recent years, use of clad metals for furnace brazing of heat exchangers has increased significantly. These brazing materials have proven to be cost effective and reliable and the properties of the materials can be tailored to the heat exchanging application. The primary materials used in these applications range from copper clad steel to copper clad stainless steel. Selection of the component metals determines the properties of the materials system and therefore provides the properties desired in the heat exchanger. This paper discusses the process used to fabricate copper clad self brazing material and for brazing heat exchangers. Factors important in the selection of a particular materials systems are described and data is provided on the properties of these materials in heat exchangers.
Technical Paper

State of the Art in Automobile Cathodic Protection

The use of cathodic protection for metals can be accomplished by sacrificial protection and impressed current protection. This paper discusses the application and misapplication of cathodic protection to automobiles. Fundamental principles and requirements for successful use of this technology are reviewed, including the important effect of electrolyte resistance on current flow. Laboratory and field tests show that in the atmospheric automobile environment, cathodic protection beyond a few centimeters from the anode is not possible. Distributing the anode, such as in galvanized steel, solves the problem for sacrificial protection and therefore, this technique is used extensively on automobiles. However, distributing the anode for impressed current protection of automobiles is not currently economical. Therefore, successful commercial application of impressed current protection of automobiles has not occurred.
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

Performance of Stainless Steel Clad Aluminum in Bumper Applications

This paper traces the development of stainless steel clad aluminum for bumper faceplate applications. Use of this material on trucks has increased due to its performance characteristics. A wide range of tests have been used to evaluate mechanical and environmental affects on the materials system. Now field results are available and will be reported in this paper.
Technical Paper

Causes and Effects of Corrosion Relating to Exterior Trim on Automobiles

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.
Technical Paper

Comparative Corrosion Behavior of Electroplated and Clad Metal Coatings

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.
Technical Paper

Corrosion Behavior of Trim Materials on 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.
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.
Technical Paper

Corrosion-Resistant, High-Strength Clad Metal System for Hydraulic Brake Line Tubing

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.
Technical Paper

Designing Clad Metals for Corrosion Control

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.
Technical Paper

Clad Metals in Automotive Trim Applications

The behavior of stainless clad aluminum automotive trim has been investigated, using modern electrochemical techniques in laboratory and field service tests. Galvanic protection of paint-damaged auto body and the corresponding sacrificial aluminum behavior with this trim material has been observed in a wide number of applications and conditions. The results obtained with stainless clad aluminum automotive trims are compared with those for other trim materials. The results are explained using modern electrochemical theories.