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Book Review: Handbook of Aluminum Bonding Technology and Data
12-12-02
Publisher: Marcel Dekker
The adhesive bonding of aluminum, either alone or in combination with other joining methods, has been a method of industrial importance in the past and promises to be more so in the future. If there's one reference that you would want to have for this technology area, the Handbook of Aluminum Bonding Technology and Data is it. It is a massive tome (790 pages, 4,686 references, 226 tables, and 59 figures), written remarkably by one person, Dr. J. Dean Minford. Published by Marcel Dekker in 1993, this book could only have been written by someone who spent essentially all of a 30 year career at Alcoa studying a wide range of technical aspects related to the bonding of aluminum.
A few general notes about the book before discussing its content in more detail. While packed with data and extensive references, this is not what one might expect from a traditional "handbook". While typically a handbook is designed for conciseness and ease of looking up information, the Handbook of Aluminum Bonding Technology and Data reads more like a textbook. It is very comprehensive, but the information the reader seeks is buried in chapters that are highly detailed and thoroughly referenced but difficult to navigate. There is no listing of Tables or Figures that would allow the reader to quickly locate data of interest, and the chapters generally lack a summary section to enable the reader to review the key points without reading the entire section. Couple this with Minford's academic writing style, and you end up with a book that is challenging to get through. But the breadth and depth of the information contained in it justifies some extra effort on the reader's part.
The Preface and Introduction in Chapter 1 of the book collectively provide some overall historical background to the development of bonding technology for aluminum. It is pointed out that the development of synthetic adhesives capable of supporting structural loading in metal products is a relatively recent development, growing from the observation in that late 1930's that hot curing wood adhesives could also adhere very well to metal oxide surfaces. The first major application in the aluminum industry was in aircraft construction. Minford points out that the order of technical development of structural bonding is unusual in this respect. Specifically, the first application of bonding in aircraft, initially in aluminum honeycomb panels and then subsequently in primary aircraft structure, required the highest state of the art to be developed first, both in terms of mechanical properties and durability of the bonded joint. The culmination of much of the work in the aircraft area was in the Air Force program entitled PABST (Primary Adhesive Bonded Structure Technology) in the mid-1970's, and in a book entitled Adhesive Bonding of Aluminum Alloys, also published by Marcel Dekker in 1985. Minford's objective is to cover a broader range of adhesives and sealants that he refers to as "the bread-and-butter lower cost and lower performance products necessary for manufacturing outside the aerospace industry", as well as the aerospace technology.
Chapters 2-5 provide the technical basis for bonding of aluminum. The factors affecting adhesion are discussed, and theories for the mechanisms of adhesion are in the categories of mechanical interlocking to a microscopically rough surface oxide and chemical bonding between the adhesive and aluminum oxide surface. On the latter point, it is noted that "an amazing aspect of aluminum is that no adhesion between the adhesives and the metal atoms is ever involved." Rather, the bonding is between the metal oxide and the adhesive, thus requiring that the nature of the oxide on aluminum needs to be evaluated and controlled to make durable joints. Extensive discussion of the nature of various aluminum oxides, produced both naturally and by artificial processes such as anodizing, is presented, as are various interactions between the surface oxide and the environment that can create complications in bonding. Specific treatments for preparing the aluminum adherend surface are provided in "recipe" fashion that will helpful to the reader involved in implementing these processes. Chapter 5 focuses on the selection of the adhesive, providing a listing of characteristics and suppliers (circa 1993) of materials in the categories of natural and synthetic elastomers, thermoplastics, thermosets (e.g. epoxy), and sealants. Again, there is a good set of tables with detailed information that will be beneficial in the selection process.
Probably the core of the book is the five chapters devoted to topics related to bond joint properties. This is not surprising, considering Minford's personal research interests, which he summarizes as "focusing on the relationship between the degree of surface pretreating and the level of long-term joint durability that could be achieved." Design of bonded joints is reviewed, and it is noted, "in creating joints it must be remembered that the challenge is to properly design joints for bonding rather than simply substitute adhesive bonding for joints previously employed for other means of joining." (This is design advice given fairly widely relative to aluminum substitutions in general.) Figure 16 in this Chapter provides a useful summary of the types of stresses in common adhesive joints, and specific joint design guidelines are given. Also, a comparative summary of structural performance of bonding relative to other structural joints is given. Failure mechanisms in bonded joints, both mechanical and environmental, are reviewed. With respect to the latter, the role of water in the service environment is the focus. Chapter 9 provides a comprehensive listing of test and evaluation specifications and methods, including mechanical, NDT, and environmental tests, for bonded joints. Again, Minford's long service to ASTM in this area is apparent in the depth of the discussion and completeness of the information. The prior chapters in this book culminate in Chapter 10, a 160 page section titled "Durability or Permanence of Adhesive Joints". While repeating some information from the prior chapters, it provides in a holistic way the issues that can affect joint performance. For the reader with a good beginning background in adhesive bonding, this chapter is probably the one worth reading in detail.
The last Chapter in the book reviews applications of adhesive bonding aluminum structures. In the first part of the chapter, the various commercial bonding processes are reviewed. The remainder deals with specific applications in aerospace, transportation (especially automotive body), electrical and electronics, construction, packaging, appliance, medical, and sporting goods markets. The chapter contains no tables or figures, and so is descriptive in nature rather than illustrative. Extensive references are given to articles in Adhesives Age magazine for further details.
This book, in addition to being available from the publisher, Marcel Dekker, can be obtained from the Aluminum Association Bookstore and can be ordered online at www.aluminum.org. For those interested specifically in the adhesive bonding of aluminum auto body panels, the Aluminum Association publication "Aluminum for Auto Body Sheet Panels", code AT-3-702616, includes a section on this topic.
Article provided courtesy of The Aluminum Association - www.aluminum.org
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