Author: Christian Vargel
Publisher: Elsevier Science (2020)
Review by Joseph C. Benedyk, Editor
In a paradoxical sense, corrosion of aluminum should be a non-issue to many users of aluminum and its alloys, as it is normally considered to be protected by a passive oxide coating that resists corrosion under many conditions. As Christian Vargel shows in the new edition of his classic book, Corrosion of Aluminium, this may be both true and also false. Despite the many advantages of aluminum, corrosion must be considered as an important mode of failure under certain conditions that are dependent on alloy type, temper, manufacturing conditions, contact media, temperature, imposed stress, pH, and combinations of same. Protection of aluminum products against corrosion is thus a critical issue in today’s applications, which basically expect a high level of performance from the hundreds of wrought and casting aluminum alloys used in a number of particularly challenging conditions and environments.
Following the first edition published by Elsevier Science in 2004, this second edition of Corrosion of Aluminium updates, revises, and expands the topic to include 200 more pages on new wrought and casting alloys, applications, and forming and joining technologies, such as friction stir welding and twin roll casting. With some 50 years of experience as an aluminum corrosion engineer, Vargel addresses this difficult topic with an approach that combines both practice and theory, providing readers with the reasoning behind aluminum alloy selection and design for a number of given service conditions in order to prevent any of the many forms of corrosion that may occur in a variety of industrial applications.
The book’s length (858 pages) and scholarship (over 2,000 references)—consisting of 13 parts (Part A to Part M) with most having multiple chapters—attest to the author’s insightful knowledge of and devotion to the subject. Having served as chief engineer for 40 years with Pechiney/Constellium and now as a consulting engineer specializing in corrosion of aluminum, Vargel approaches his subject with a deep understanding of both the practical and theoretical aspects of corrosion. He presents the mechanisms and surface interactions in different aqueous and nonaqueous atmospheres for aluminum and its alloys, often in comparison with competing metals such as copper and steel. This makes it an excellent textbook for metallurgy and engineering students who will face corrosion problems with aluminum in the future. It also makes for an excellent, practical reference book for aluminum specialists and users who cope daily with design and engineering issues with aluminum products in the many markets served.
Although aluminum is often considered corrosion resistant due to its passive metallurgically bonded oxide layer, it falls prey to corrosion attack in various types of aqueous and nonaqueous media, bases, acids, freshwater, seawater, industrial chemicals, sulfides, gases (e.g. hydrogen), etc., even if anodized or painted. Vargel describes the effects of these various media (including soils and structural materials) when they come in contact with aluminum and its alloys. He explains how the surface and subsurface are attacked and presents copious supporting data on the variables that promote corrosion in specific aluminum alloys. The mechanisms and effects of stress corrosion and corrosion fatigue on aluminum alloys along with practical preventative measures are presented in several chapters. Filiform corrosion, which damages the decorative appearance of coated aluminum members, especially critical in B&C and automotive applications, warrants a separate chapter as well.
One of the critical issues addressed in the book is the role of the aluminum surface condition and the different factors to consider for the formation of the passive oxide coating, which depends greatly on the Cl– ion concentration, pH of the medium, and temperature to protect the subsurface aluminum. Based on the open circuit potential of bare aluminum, -1.66 V measured in a standard hydrogen electrode (SHE), aluminum is easily oxidized. Vargel describes the electrochemistry of this reaction in various media and notes the effects of alloy composition and intermetallic compounds on the quality of the oxide film, all investigated by modern experimental techniques. He also notes the importance of the surface and mechanically modified subsurface (50 nm-1 µm) condition on aluminum corrosion.
Part F of the book deals with protection of aluminum against corrosion. Again, why bother if aluminum is supposed to resist corrosion? Vargel explains, “This depends on the alloy, applications and use.” He offers various corrosion protection options: boehmite coatings, chemical conversion treatments, anodization, micro-arc oxidation, coatings of sol-gels, silanes, polyanilines, organics, cladding, plating, corrosion inhibitors, and cathodic protection. The numerous examples in these categories of corrosion protection are offered with practical applications of the given aluminum alloy and use.
Almost half of the book deals with the effects of individual alloying elements and processing conditions for all the classes of wrought and casting aluminum alloys on the various corrosion modes discussed in previous sections (a separate chapter covers Al-Li alloys). The wealth of detail in data presentation and organization of the parts and chapters of the book make it easy to focus on any aluminum alloy and/or potential corrosion hazard, just as in a technical handbook. Every class and type of aqueous and nonaqueous media that affects corrosion of aluminum is cataloged in the final parts of the book.
A welcome addition to technical libraries, Corrosion of Aluminium takes on this challenging topic in both scientific and practical terms, offering an all-inclusive analysis of the subject—a corrosion classic in every sense. Despite its significant length, readers can easily find sections of interest, as the book is well organized in its 13 parts, with multilevel listings of topics and indexing.