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Book Review: Publication AT7
12-26-02
Publisher: The Aluminum Association - Automotive & Light Truck Group
While much of the interest in the use of aluminum in the automotive market results from its light weight, the corrosion resistance of the material is certainly another key benefit. As new car prices increase (they quadrupled between 1978 and 1999), durability and corrosion resistance take on new importance. That is something that aluminum can provide, as automakers offer longer warranties against component failure and body rust-out. A recent publication from the Aluminum Association's Automotive and Light Truck Group, Publication AT7, was just issued in May 2001 that addresses the corrosion aspect from a number of different perspectives.
The initial sections provide background on the use of aluminum in automotive applications. An historical perspective on the use of aluminum in automobiles is provided. Initial applications were at the turn of the century (the 20th century), and in the pre-World War I period, the auto industry was aluminum's single largest market, absorbing nearly half of the material produced. After World War II, the increased capacity of the aluminum industry developed for the war effort was available to the automotive industry. Applications in automobiles (as well as other forms of transportation) steadily grew, both in the body and powertrain areas, to over 100 different components today. Automotive applications have grown from 54 pounds/car or 1.4% of the total weight in 1960 to 250 pounds/car or 8% of the total weight in 1999. A further section entitled "Versatile, Tough, Durable…Aluminum Parts in the Cars of Today" provides an "A-W" alphabetical sampling of the wide range of applications in which aluminum has been used, briefly discussing the key aluminum attributes utilized in each. The final preliminary section summarizes the key characteristics of aluminum that makes it the material of choice in many automotive applications.
With this background, the topics of durability and corrosion resistance are addressed specifically. The inherent ability of aluminum to form a protective oxide is the key to its inherent corrosion resistance. Because this oxide is tightly adherent and transparent, many commercial vehicles made in aluminum are used unpainted, and aluminum has proven durable in these applications. Coatings are applied to aluminum in cases where additional corrosion protection is required or for aesthetic reasons. Examples of the coatings typically applied are anodic coatings, chemical conversion coatings, and painting.
Design of parts made form aluminum to minimize corrosion attack is also important. This publication describes the main forms of corrosion that are of concern for automotive applications, specifically galvanic, crevice, filiform, and poultice corrosion along with intergranular and stress corrosion cracking. Avoiding or minimizing these types of corrosion through design involves attention to joints and faying surfaces, entrapment areas, and the orientation of structural members and reinforcements. The latter in particular addresses the need for open construction to facilitate draining.
The publication concludes with references in the areas of automotive design, corrosion resistance, and aluminum properties and characteristics. An Appendix containing more detailed information on the properties of commonly used aluminum body sheet and extrusion alloys such as compositions, physical and mechanical properties, and comparative characteristics in the areas of general corrosion, formability, and weldability, is also included.
This publication is available for the Aluminum Association Bookstore online at www.aluminum.org
Article provided courtesy of The Aluminum Association - www.aluminum.org
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