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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.

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.

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.

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.