Asm Specialty Handbook Aluminum And Aluminum Alloys Pdf
Su Strawderman
This one-stop reference is a tremendous value and time saver for engineers, designers and researchers who select and process aluminum and aluminum alloys. Covers all aspects of the selection, processing, properties, and performance of aluminum.
Emerging technologies, including aluminum metal-matrix composites, are combined with all the essential aluminum information from the multiple-volume ASM Handbook series (with newly updated statistical information) and other authoritative ASM sources.
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The first step: Understand the alloy and temper designations for the specific stamping being processed. Aluminum alloys are designated by a four-digit code that describes their primary alloying elements (Table 1).
The 2xxx series alloys exhibit high strength, toughness and, in some cases, weldability. They do not resist atmospheric corrosion as well as other aluminum alloys do, so they typically are painted or clad for added protection.
The 5xxx series alloys find use in consumer electronic cases (strength, appearance and anodizing) and automotive structural components. Since this series of alloys is not heattreatable, any beneficial strengthening from cold working may be lost if the final part is subjected to a paint-bake cycle.
Determining an appropriate cutting clearance between punch and die depends on material type and thickness. Suggested punch-to-die clearances, in terms of percent of sheet thickness (t), also are provided in Table 2 for cutting, blanking and hole punching.
When punching and cutting aluminum, especially dead-soft alloys (O-temper), metalformers must closely follow the appropriate maintenance routines, and use sharp tooling. Dull edges on punches and dies can produce burrs similar to those caused by excessive clearance, with burr height being particularly problematic. A lubricant suitable for aluminum stampings will help reduce tool wear and produce quality shear edges.
Bending aluminum requires special attention of the die designer. While for most steels the minimum bending radius relative to sheet thickness is approximately constant, primarily because ductility (total elongation) tends to be the limiting factor, this is not the case with aluminum. In general, the ratio of bend radius to sheet thickness will increase with sheet thickness (Table 3).MF
6463-T5 aluminum is 6463 aluminum in the T5 temper. To achieve this temper, the metal is artificially aged until it meets standard mechanical property requirements. It has the second lowest ductility compared to the other variants of 6463 aluminum.
The graph bars on the material properties cards below compare 6463-T5 aluminum to: 6000-series alloys (top), all aluminum alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.
The finish can be too thin, non- uniform and/or have an unfavorable appearance. These are common problems with a variety of practical solutions; they are easy to recognize, but in many instances, the source for the problem remains unknown. Critical to solving the problems of anodizing die castings is understanding the die cast substrate and the impact of surface condition, alloy composition, casting quality and microstructure on the anodizing process. Substrate quality issues are just as important, maybe more so, than anodizing conditions and technique.
Dr. Mary Jude Runge and Larry ChesterfieldCertain optimum anodizing conditions may be used in some cases to help overcome less than advantageous metallurgical conditions. These include well known processing tools such as various pretreatment chemistries, higher anodizing bath concentration, and higher bath temperatures. These, and other recommended solutions are not successful in every case; sometimes trial and error testing on actual production parts must be done to find the best processing techniques. Through the use of actual case studies that provide real-life solutions in terms of anodizing theory and interfacial science, this paper provides some explanations by tying together metallurgical science with anodizing practice.
Consideration given to solve these rather easy-to-identify problems has illuminated four broad areas for discussion: 1) alloy selection, 2) substrate surface treatment, 3) anodizing process parameters, and 4) substrate quality. Of the four, perhaps the metallurgical factors that impact substrate quality: alloy composition, casting quality, microstructure and surface quality are dominant in determining anodizing conditions, technique and quality.
This paper will cover each of the four areas by discussing, in limited detail, the impact each has on the interface from which the anodic oxide originates and grows. Theoretical scientific reasons for why the problems occur and why most solutions succeed and some fail are followed by case studies that present actual problems and practical solutions based in the scientific background. The limitations as to what can be done from an anodizing standpoint to overcome the metallurgical condition of a cast substrate are presented not as an excuse, but as a call for understanding and communication between metal finishers, component designers who would like to use die castings, and the foundries who pour the castings in order to optimize product and process and to increase the use of anodized cast aluminum components.
Sand, Permanent and Semi Permanent Mold, Die Casting, and other related methods are all utilized today to provide cast aluminum product. The method of choice usually depends upon component size and design, lot size, and alloy requirements. Of these methods, die casting accounts for almost 70% of the total cast aluminum products available worldwide.
Aluminum die castings have been commercially available since the beginning of the 20th century. Castings are used for a variety of applications, from decorative sculptures and jewelry to automotive pistons and engine blocks.
Die casting is a versatile process for producing engineered metal parts by forcing molten metal under high pressure into reusable steel molds. These molds, called dies, can be designed to produce complex shapes with a high degree of accuracy and repeatability. Parts can be sharply defined, with smooth or textured surfaces, and are suitable for a wide variety of attractive and serviceable finishes.9
Figure 1: Examples of components die cast from alloy AlMg9 (similar to alloy 520), with corresponding microstructure (right). Multiple phases and intermetallic compounds are present throughout the microstructure as Mg2Si precipitates, hypoeutectic silicon and a fine network of Mg5Al8. When non- aluminum alloy constituents intersect the surface, they can interfere with the anodizing reaction.First and foremost, cast alloys are formulated for strength, hardness, and resistance to wear and fatigue. In aluminum casting operations, these properties are produced metallurgically two ways: (1) by solid solution hardening; that is: by the substitution of aluminum atoms with alloying atoms in the aluminum crystal structure and (2) by precipitation hardening: the dispersion of second phase constituents or elements in solution and precipitating them out as small intermetallic compounds, incoherent with the microstructure, which inhibit material deformation. Cast components have limited ductility and can be brittle; therefore, castings are not usually meant for subsequent deformation processing. Other than minimal finishing processes such as machining, a casting is typically produced to function near net shape.
Because cast components are produced to function near net shape, castings can be alloyed beyond what is typical for wrought products; that is, additions of other elements are at a higher per cent than the additions for alloys intended for extruded, rolled or deep drawn product (up to 16% total alloy content for castings vs. up to 8% for wrought alloys). As such, cast alloys are metallurgically more complex than their wrought counterparts; increased alloy additions produce correspondingly higher levels of solution phases, intermetallic compounds and precipitates. Castings, therefore, in addition to their strength and fatigue resistance, exhibit more complex surfaces, with less free aluminum, which make them more difficult to anodize. See Figure 1.
The casting process and the alloy chemistry affect the level of microstructural homogeneity, the defect population and the variation of chemical potential across a cast component surface. It is important to understand the nature of the surface and therefore the interface between the component surface and the anodizing electrolyte such that anodizing process parameters can be modified to effect optimum oxide growth. This summary of cast alloy designations, compositions, and alloying elements is included for the understanding of three things: 1) how they affect the casting process, 2) how they affect the mechanical properties of the finished casting and 3) how they affect the surface, and therefore the anodizing process.
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