The following article appears in the journal JOM, 53 (2) (2001), pp. 21-25

Wrought and Sheet: Overview

Technology Innovation in Aluminum Products

TABLE OF CONTENTS
INTRODUCTION DIRECT-CHILL CASTING HEAT-TREATABLE ALLOYS TWO-PIECE BEVERAGE CAN ALUMINUM EXTRUSION CONTINUOUS MOLTEN METAL TREATMENT ALLOY 6061 ELECTRICAL CONDUCTORS CONTINUOUS CASTING SHAPE-CASTING ALLOY A356 EXTRUSION PRESS QUENCHING CONCLUSION ACKNOWLEDGEMENTS References
Figure 1. Distribution of aluminum shipments by (a-top) major market and (b-bottom) product form in major U.S. markets (based on 1999 information).1

In 2001, the aluminum industry continues to benefit from technical innovations made in alloy development, product-manufacturing technologies, and processing equipment over the last century. This paper examines the top ten alloy, product, and process developments that have shaped the industry’s production methods and markets. The inter-relationships among the alloy development, process innovations, and markets are highlighted. Omitted are details about patent literature or the inception of many technologies; the major criterion for placement on the list was impact on the total industry.

INTRODUCTION

The aluminum industry has evolved over the past 100 years from the limited production of alloys and products to the high-volume manufacture of a wide variety of products. Today’s U.S. aluminum production includes roughly 5.6 million tonnes of flat-rolled products, 1.7 million tonnes of extrusions and tube, and 2.4 million tonnes of ingot/castings.¹ These products are used in a wide variety of markets, including building and construction, transportation, and packaging. Markets also exist for such products as electrical conductors (EC), forgings, rod, wire, bar, and powders and pastes, as shown in the “other” category in Figure1.

Following is an analysis of ten innovations that influenced aluminum production methods and markets. Although Alcoa was the source of much of the historical perspective, two factors may excuse this to some degree:

• Many of these developments took place before the birth of Alcoa’s major competitors.
• While Alcoa’s early technical history is well documented, little was found in the open literature on early European developments.

DIRECT-CHILL CASTING

Casting in the early days of aluminum production consisted of making 45 kg ingots in steel-tilt molds.² As shown in Figure 2, the family of alloys that could be offered to aluminum customers was growing by the 1920s. Supplies were limited by difficulties with casting and ingot quality, however. The tilt molds suffered from macrosegregation, porosity, and a tendency toward severe shrinkage cracking when the alloy content increased. Alcoa fabricating plants coped with casting inefficiency, poor ingot quality, and size limitations. Recovery losses were realized as the tilt molds had to be “scalped” substantially to remove undesirable surface segregation.

William T. Ennor, of Alcoa’s Massena operations, devised the idea of directly impinging water on the solidified shell of an ingot as it was cast. Using the direct chill (DC) process, it was possible to drop the ingot continuously and avoid the turbulence associated with pouring metal into the old tilt molds. Ennor’s patent³ provided the basis for modern DC-casting technology, which was introduced into virtually all of Alcoa’s plants during the 1930s. The plants built by Alcoa for the war effort incorporated this technology to make aluminum products for the aircraft industry. In 1951, just after Alcoa’s Davenport works was completed, the largest aluminum ingot fabricated was approximately 3.1 tonnes.⁴ During the 1950s, DC ingots were available to make the large products needed by the aerospace, marine, and transportation industries. Size increases continued over the years—today’s sheet ingots may reach 15.5 tonnes and extrusion billet are produced as large as 1.2 m in diameter. Figures 3a and 3b show typical cast sheet ingot and extrusion logs used in today’s aluminum industry.

In addition to allowing for larger ingots, DC casting helped improve product characteristics. Figure 4 shows the advancements in average mechanical properties and fatigue-endurance limit for alloys 2024 and 2017 as DC casting became the standard within the U.S. aluminum industry.⁵ On the process side, it became necessary to re-engineer the downstream paths for some products. Alloy 3003 tilt-mold ingots, which cooled extremely slowly after solidification, required only modest thermal treatments to produce fine-grained products. However, the more rapid solidification of DC ingots resulted in significantly more manganese in solution as well as problems with coarse grain size. W.A. Anderson and others solved those problems by applying high-temperature homogenization practices to the ingot.

As the product-size capabilities increased with DC casting, so did the capability to develop new alloys, such as high-strength alloy 7075, introduced during World War II. In the 1950s, new markets for shipbuilding required large ingots of higher magnesium 5xxx alloys such as 5086 and 5083. Other high-magnesium alloys, 5082 and 5182, were developed in conjunction with horizontal DC casting in the 1960s to supply the growing can-sheet market. Today’s complex, higher solute 2xxx and 7xxx alloys could certainly not be cast in the sizes needed for aerospace applications without high quality DC ingot. Neither could the coils of 3xxx or 5xxx alloy can sheet be produced in the economic sizes demanded by the beverage-can industry.

Figure 2. A timeline for aluminum product development.

HEAT-TREATABLE ALLOYS

Figure 3. Typical DC cast (a-top) extrusion logs and (b-bottom) sheet ingot used in the manufacture of modern aluminum wrought products.

Figure 4. Improvement in minimum mechanical properties and typical fatigue performance of alloys 2024 and 2017 in the T4 temper made possible largely by using DC-cast ingot for the manufacture of wrought products.

Much has been written about the accidental discovery of aluminum alloys’ heat-treatable capability ⁶,⁷ by German researcher A. Wilm in 1908. During World War I, the Germans produced Duralumin for 80 airships—more than 726 tonnes in one year.⁸ Alcoa obtained the rights to Wilm’s patent after World War I and began research that led to alloys such as 25S (2025), 14S (2014), and aluminum-magnesium-silicon alloy 51S (6051), which were easier to fabricate than Duralumin. Forged aluminum propellers were used on airplanes as early as 1922. By 1936, the major heat-treatable systems, aluminum-magnesium-silicon, aluminum-magnesium-copper, and aluminum-magnesium-zinc, had been mapped out by researchers.⁹

With its improved strength, aluminum played a key role in the development of higher-performance aircraft.¹⁰ The 2xxx (aluminum-copper) alloys quickly reached a plateau with the development of 24S (2024) in 1933, in which the aluminum-magnesium-copper phase diagram was exploited for maximum solubility. Because of their high strength, toughness, and fatigue resistance, modifications of 24S as well as the original alloys are still widely used today for aircraft applications.

Alloy 75S (7075), developed during World War II, provided the high-strength capability not available with aluminum-magnesium-copper alloys. Modifications to the base alloy composition resulted in higher toughness (alloys 7175 and 7475) while the T7xx tempers alleviated stress corrosion and exfoliation problems inherent with the T6 temper. The composition of alloy 7050 was designed to reduce quench sensitivity in thick-section T7xx products. Additional development has extended the ability of aluminum alloys to reduce weight and increase aircraft performance. This development continues today, with the T77 tempers being utilized with special alloy compositions to attain levels of strength and corrosion performance not matched by previous materials.

TWO-PIECE BEVERAGE CAN

With nearly 200 billion produced worldwide last year, aluminum cans are probably the most recognized consumer package in the world. More than 1/3 of the U.S. market for flat-rolled products is can sheet, with 1.9 million tonnes shipped in 1999. The demand for can sheet has driven continuous improvements in all aspects of the sheet production process, including technology to make recycled cans a preferred and economical source of metal for new cans.

Commercial cans initially were produced by Coors Brewing Company from impact-extruded 1xxx-O slugs and, later, from relatively thick 3xxx-O sheet. The real breakthrough, though, came when Reynolds Aluminum developed draw-and- iron technology for the use of hard (H18 and H19) tempers.¹¹ This technology allowed for considerable reduction in metal thickness, and, therefore, more economical, lightweight cans. The technological aspects of can-making are described in Reference 11.

Continuous innovation on a number of fronts has kept the can competitive against other materials. After draw-and-iron technology reduced the can weight, the lid and tab became lighter also. Although alloy development contributed to the weight reduction, the most dramatic changes resulted from advances in can design and forming technology.

Perhaps equal in importance to the development of draw-and-iron technology were the alloy and process innovations associated with the can lid. The development of high-strength alloy 5182 in 1967 reduced the lid thickness to help make the cost of aluminum competitive with steel.¹² Aluminum pull tabs were introduced as early as 1961, followed by the invention of tabs that remained attached to the cans, which prevented the litter associated with detached tabs.¹³

When the growth of the can market sparked the need to find economies of scale in sheet production, the aluminum industry re-invented the rolling process. Four-high and, later, six-high rolling mills were needed to provide the tight thickness tolerances necessary as cans became lighter in weight. Tandem rolling mills, with as many as six stands, were used to reduce the number of rolling passes. Improvements in rolling lubricants and control technologies enabled the mills to roll sheet more consistently, faster, and with fewer cobbles. Today’s can sheet mills are often highly streamlined, producing large volumes of consistent can-body or lid-stock product.

Several highly specialized 3xxx and 5xxx (aluminum-magnesium-manganese) alloys have been developed to meet the demands of the can industry. While the body-stock alloy and microstructure were customized particularly for the wall-ironing process, the 5xxx lid alloy was developed for higher strength and good formability after thermal exposure during the coating process. The need for product consistency also drove metallurgists to understand the rolling process, particularly the recrystallization mechanisms that govern the texture and earing behavior (i.e., anisotropy) of can sheet. The pursuit of anisotropy control in can sheet elevated the level of physical metallurgy of non-heat-treatable aluminum alloys over the last 20 years.¹¹

Recycling technology, too, has had to keep pace with the demand for metal units used in the can market. Can-collection, baling, shredding, delacquering, and melting technologies have all combined to improve the quality and economics of beverage-can recycling. Recycled aluminum cans continue to be a major source of metal for new cans. In 1999, over 862,000 tonnes of aluminum canswerecollected intheUnitedStates,¹⁴ representing a recycling rate of 63.9%.

ALUMINUM EXTRUSION

Figure 5. A range of extruded aluminum used in modern industry: (a-top) microvoid hollow extrusions for heat exchangers (shown in cross-section), (b-bottom) extruded aerospace shapes.

The hydraulic-extrusion press dates to the early 19th century, well before the Hall-Héroult process for making aluminum. During the 1800s, the process was proven for lead and copper products. Although attempts by J.W. Hoopes of Alcoa in 1902–1904 to produce conductor wire by a vertical-extrusion process were unsuccessful,¹⁵ his experiences led the way for extrusion to be used for other products.

In 1905, Alcoa bought an extrusion press and hired Louis de Cazenove to run it. The first aluminum extrusions were done at Alcoa’s Massena operations, but the equipment was moved to the New Kensington, Pennsylvania works, where commercial extruded shapes were available after several years of experimentation. In this process, the aluminum was solidified in the extrusion chamber and forced vertically downward through a die. As the product size and extrusion pressures increased, the extrusion process was changed to use a horizontal press. By 1923, Alcoa was using horizontal presses with preheated billets.¹⁶

Today, the 1.5 million tonne market for aluminum extrusions includes applications from building and construction to aerospace components. Extruded products, which encompass virtually all of the alloy families, range in size from millimeter-sized microvoid hollow sections for heat exchangers to large wing structures for airplanes. Extrusions are also the feedstock for aluminum wire, drawn tubing, and rod and bar products. Figures 5a and 5b show examples of extruded products made in today’s aluminum industry.

CONTINUOUS MOLTEN METAL TREATMENT

As larger ingots were made possible by the DC-casting process, quality requirements became more stringent for a wide variety of products. Products that would have been acceptable in the 1940s could not pass new, ultrasonic requirements or produce the surface finish required of polished, chemically treated products. As large 5xxx ingots were hot rolled, lower levels of sodium and calcium were required to prevent edge cracking. Low hydrogen levels were needed to prevent blisters in the heat-treated products of other alloys.

Typical early methods consisted of fluxing the furnace with chlorine to remove hydrogen, then allowing the inclusions to settle before casting. These methods were inefficient, ineffective, and environmentally unsound.Those factors drove the need for better metal-treatment methods.

Deep-bed filtration (the Alcoa 94 process) used tabular aluminum balls and chat to trap oxide inclusions as the metal flowed from the holding furnace to the casting pit. The Alcoa 181 process introduced argon into the bed filters to assist hydrogen removal,¹⁷ but avoided the use of chlorine, which could clog the filters with molten salts. One breakthrough came with the development of internally heated bed filters, which allowed the size of the units (and metal flow rates) to be increased substantially. Also important was the introduction of the Alcoa 622 process, which used a spinning nozzle to inject a fine dispersion of argon-chlorine gas bubbles into the molten metalto remove impurities.The process, which used very low percentages of chlorine (1–10%), was successful in reducing emissions while maintaining internal ingot quality.

An important side benefit of in-line metal treatment was the introduction of continuously fed grain refiners. With large filter boxes, titanium-bearing grain refiners could be fed in-line at the desired rate without settling out in the furnace. Among the benefits of the continuous-grain-refiner additions were reductions in ingot cracking, more uniform ingot structures, and improved forgeability. Another advance in metal filtration came with the introduction of rigid, ceramic foam filters. Those filters allowed the metal to be cleaned just prior to casting and offered an inexpensive, smaller-volume alternative to the large, continuous bed filters.

Some of the product benefits enabled by new, in-line metal treatments were improved fatigue performance of aerospace products, fewer pinholes in thin aluminum foil, fine aluminum wire, sheet that would not fracture during can forming, and higher surface quality in both as-fabricated and machined conditions. The major processing improvements that resulted from higher-quality ingot were reduced edge cracking and blistering during hot rolling of 5xxx ingot. Today, many new and efficient methods are available for filtration and molten-metal treatment.These commercially available processes are selected based on a combination of cost, molten-metal flow rates, and customer requirements.

ALLOY 6061

Figure 6. Typical forged (a-top) automotive wheels and (b-bottom) truck wheels produced from alloy 6061 for the transportation market.

The first commercial aluminum-magnesium-silicon alloy (51S) was developed and brought to market by 1921.¹⁸ The introduction of alloy 61S (6061) in 1935 filled the need for medium-strength, heat-treatable products with good corrosion resistance that could be welded or anodized. Alloy (62S) 6062, a low-chromium version of similar magnesium and silicon, was introduced in 1947 to provide finer grain size in some cold-worked products. Unlike the harder aluminum-copper alloys, 61S and 62S could be easily fabricated by extrusion, rolling, or forging. These alloys’mechanical properties were adequate (mid 40-45 ksi range) even with a less-than-optimum quench, enabling them to replace mild steel in many markets. The base composition was a ternary aluminum-magnesium-silicon alloy with small amounts of copper for strengthening and chromium for recrystallization control.

Alloy 6061 evolved after its initial development until, in 1963, the alloy limits were broadened to effect its combination with alloy 6062. In Europe, alloy 6082 is used more commonly than alloy 6061. Mechanical properties are similar, but, rather than chromium, manganese is used for recrystallization control.

The corrosion resistance of alloy 6061 even after welding made it popular in early railroad and marine applications, and it is still used for a variety of products. The ease of hot working and low quench sensitivity are advantages in forged automotive and truck wheels (Figures 6a and 6b.) Also made from alloy 6061 are structural sheet and tooling plate produced for the flat-rolled products market, extruded structural shapes, rod and bar, tubing, and automotive drive shafts.

ELECTRICAL CONDUCTORS

The electrification of the United States just after the turn of the century came at an ideal time for the aluminum industry to develop its first significant large-volume market. As smelter production increased and aluminum’s price decreased, its competitive position versus copper improved. At the same time, electrical-conductor cable became a viable product, with J.W. Hoopes investigating ways to produce the new product in 1902. ¹⁹ After abandoning the extrusion process, Hoopes developed alloys with sufficient conductivity but low strength. He solved the strength problem by reinforcing the soft aluminum wire with steel. This aluminum conductor steel-reinforced (ACSR) wire outperformed copper at a lower cost and withstood extremes in temperature. A patent for the product was granted in 1908 and by 1929, 482,803 km of aluminum conductor spanned the United States.²⁰

The development of the high-volume ACSR product was a critical technical milestone.¹⁹ Because of competition in this market, the aluminum product was subject to continuous improvement in its conductivity and consistency. Hoopes and others went on to develop processes to refine aluminum to 99.99% purity. Testing methods and quality-assurance procedures were put into place to guarantee that the product would provide consistent electrical and structural performance. Later refinements to electrical conductor alloys have resulted in higher strength levels without significant losses in conductivity.

CONTINUOUS CASTING

The development of continuous casters for aluminum products has been well documented over the past 50 years. While patents for continuous casters date back to the 19th century, the first commercial application of continuous casters can be attributed to Properzi.²¹ The wheel/belt caster was used to produce low-cost electrical-onductor wire in 1948. One of the first slab casters, introduced by Rigamonti in the early 1950s, cast narrow strip, roughly 100 mm by 20 mm thick. Other casters developed during the 1950s by Pechiney, Alcan, and Hunter Douglas were also limited to narrow widths (250 mm) and produced small-volume niche products. One notable high-volume application where width did not matter was Coors’ use of the process to produce stock for impact-extrusion slugs for its first generation of aluminum cans. Narrow casters of this type are still widely used today for making impact-extrusion stock.

The most important developments in aluminum casters, though, were those that enabled the manufacture of wider products. That capability made continuous-caster processes competitive with hot mills for foil and some common alloy products. Hazelett developed a twin-belt casting process that used mild steel belts and fast film water cooling to make a slab which was continuously hot rolled to coil. One of the first successful Hazelett casters was installed by Alcan in 1959.²²

A modified Hazelett caster at Alcan’s Arvida works in Canada began producing reroll coil from 1xxx, 3xxx, and 8xxx alloys in 1971. In 1981, the Hazelett unit was replaced by a wider, twin-belt machine designed by Alcan.

The Hunter twin-roll caster, developed in the 1940s and commercialized in the early 1950s, produces strip from two water-cooled steel rolls. Roll cast strip is typically 5–10 mm thick and continuous improvement by Fata-Hunter, SCAL (Pechiney) and others has resulted in commercial widths of more than 2,100 mm. Twin-roll casters are, by volume, the largest producers of continuously-cast aluminum flat-rolled products, with more than 260 casters in production worldwide. A typical roll caster in operation is shown in Figure 7.

Figure 7. Continuously-cast strip exiting a twin roll caster.

Continuous casters have greatly changed the landscape of the U.S. flat-rolled products industry by avoiding the high capital costs of conventional ingot/hot rolling facilities. The elimination of DC casting, scalping, and much of the breakdown rolling costs typically lowers operating costs significantly. In North America, nearly 25% of U.S. sheet and foil volume is produced by either roll or slab casters. The primary markets for continuous-cast sheet have been building products, household foil, fin stock, and formed containers. When hot-mill sources are not available or surface requirements are not as stringent, it has been used successfully for sheet products such as lithographic sheet. To date, the use of continuous-cast products has been mostly limited to low-solute alloys (typically 2.5% magnesium or less). Slab casters have produced some higher magnesium alloy sheet for tab or coated lid stock for beverage containers.

Similar economies are seen where continuous casters have replaced the extrusion process. Redraw rod for making wire ranging from nails to screen wire is produced from bar casters similar to those developed originally by Properzi. Electrical-conductor wire is manufactured almost entirely with continuous-cast production, enabling larger and more consistent coils to be supplied to the customer. Alloys produced on bar casters range from the electrical-conductor grade 1xxx series to higher-solute alloys such as 5154 and 6061.

A more detailed review of equipment development and process parameters for a broad range of the early continuous casters is given in Reference 23.

SHAPE-CASTING ALLOY A356

The sheer volume of aluminum shape castings used in the industry over the years makes the development of alloys with good fluid-flow characteristics and useful mechanical properties after heat treatment one of the most important innovations of the aluminum industry. By 1921, Archer and Jeffries had developed alloy 195, a heat-treatable sand-casting alloy suitable for a variety of uses.²⁴ Many of the first applications for castings were for architectural spandrels used in building construction. One of the notable applications of castings produced at Alcoa’s Cleveland works was for the exterior of the Empire State Building. Aluminum cast pistons and aircraft engine blocks quickly came into use in the early 1920s. In 1928, the 11,340 tonnes of heat-treated cast products also included washing-machine agitators, vacuum-cleaner bodies, and food-processing equipment.

The early casting alloys were based on achieving a given level of heat-treated strength. A significant cast alloy improvement was the introduction of alloy A356. Lemon, Hunsicker, and coworkers²⁵ reduced iron content to free more copper for precipitation hardening and reduce insoluble constituent particle content. The cleaner microstructure improved ductility, corrosion resistance, and other secondary properties, opening up a number of new structural markets for aluminum-cast products.

Today, more than 90 different compositions are registered by the Aluminum Association for the production of aluminum castings.²⁶ These alloys are tailored to the end-use properties, economics, and casting method. While many of the cast alloys are an important use for secondary (recycled) aluminum, some of the alloys require high levels of pure metal to achieve the desired product requirements. Die, permanent mold, and sand castings make up the vast majority of cast structural applications. Engines, transmissions, and cast wheels dominate the tonnage of castings used for light vehicles.²⁷

EXTRUSION PRESS QUENCHING

Facing competition from wood and plastic for the building-products market, the need for an inexpensive aluminum product was paramount. Today’s largest market for aluminum extrusions is in the building and construction market, where in 1999, U.S. production was almost 635,029 tonnes.²⁸ The marriage of market need, alloy, and process was critical for making aluminum extrusions successful in this market. Low extrusion pressures for soft 6xxx alloys make them ideal for complex shapes and hollows, which helps simplify customer joining and assembly. The press-quenching process eliminates the need for a separate solution heat-treatment step and is critical to making a low-cost product with reasonable strength.

Press quenching at Alcoa had a thoroughly pragmatic origin in the early 1930s, unrelated to the building-products business. When it was necessary to make alloy 2117 extrusions that werelonger than existing heat-treatment furnaces, hand-held hoses were used to water-quench the extrusions on the runout table.²⁹ At about this same time, alloy 6053-T5 was introduced, meeting mechanical property limits by cooling in ambient air on the runout table. As customers required larger-diameter products from this alloy, it was discovered that forced-air cooling on the table was necessary to achieve the desired strength levels for the T5 temper.

Alloy 6063 was introduced in 1944 for extruded products. Because it was a heat-treatable, low-solute aluminum-magnesium-silicon alloy, it could be extruded at high rates, yet age-harden to adequate strengths. In addition, the alloy could be anodized and colored easily, and the corrosion resistance was superior to that of alloy 6061. The low quench sensitivity of alloy 6063 insured press heat treatment with moderate cooling rates, enabling complex sections to be produced with minimal quench distortion.

Today’s market needs for extruded building and transportation products are met by a variety of alloys and processing methods. Alloy 6463, with low iron, is suitable for applications where a bright, anodized finish is required. An even lower solute (and higher productivity) alloy 6060 is used where the strength of alloy 6063-T5 is not needed. Extrusions may be quenched by air, mist, sprays, standing wave, or quench tank, depending upon the geometry and final product needs. Low-copper 7xxx alloys are also commonly press quenched for a variety of applications ranging from bridge decks to automotive bumpers.³⁰ These alloys include 7005, 7003, and 7108.

CONCLUSION

What conclusions and lessons for the future can we draw from the last 100 years of successful product and process developments?

• The market will drive the selection of alloy, process, and product form to the low-cost, functional alternative. Economic considerations will be paramount as aluminum products defend their territory or go after new markets against competitive materials. To this end, lower-cost metal units (recycling) and process alternatives will continue to be pursued.
• For markets where material cost is not the primary driver, alloys and processing methods will likely become even more highly specialized. Unique combinations of product properties and attributes will be necessary for high-performance, likely low volume, applications.
• Understanding the real functional advantages and limits that an aluminum product brings to the end customer will be essential for future innovation. A product solution can be successful by saving the customer assembly costs or providing lower operating-life-cycle costs.
• Low density and product versatility have been keys thus far in expanding aluminum’s fast-growing transportation market. Future developments should exploit new design, joining, and finishing methods to combine the attributes of various mill products to meet the needs of the customer.

ACKNOWLEDGEMENTS

The author thanks the many Alcoa employees, present and retired, who contributed to this historical perspective either by direct conversation or by carefully describing their research in internal or external reports. A particular gratitude to a number of retired Alcoa employees whose service dates reach back as far as 1937: Harold Hunsicker, John Hatch, John Jacoby, James T. Staley, and Ronald Bachowski. Excellent detailed accounts of much of this history are found in References 4, 16, and 19.

References

1. Aluminum Statistical Review for 1999 (Washington, D.C.: The Aluminum Association, Inc., 2000).
2. C.C. Carr, Alcoa, An American Enterprise (New York: Rinehart and Company, Inc., 1952).
3. W.T. Ennor, U.S. patent 2,301,027 (1942).
4. J.D. Edwards, F.C. Frary, and Z. Jeffries, The Aluminum Industry, Vol. 2 (New York: McGraw-Hill, 1930).
5. Harold Y. Hunsicker, Alcoa Technical Center (retired), personal communication.
6. Z. Jeffries, “Two Decades of Precipitation Hardening Alloys,” Metals and Alloys, 1 (1) (1929), pp. 3–5.
7. H.Y. Hunsicker and H.C. Stumpf, History of Precipitation Hardening, Sorby Centennial Symposium on the History of Metallurgy (New York: Gordon and Breach Science Publishers, 1965).
8. J.D. Edwards, F.C. Frary, and Z. Jeffries, in Ref. 4, p. 234.
9. Harold Y. Hunsicker, Alcoa Technical Center (retired), personal communication.
10. J.T. Staley, J. Liu, and W.H. Hunt, Jr., Advanced Materials and Processes, 152, (4) (October 1997), pp. 17–20.
11. W.F. Hosford and J.L. Duncan, “The Aluminum Beverage Can,” Scientific American (September 1994), pp. 48–53.
12. W.A. Anderson and J.K. McBride, “Alloy 5182,” U.S. patent 3,502,448 (1970).
13. E.D. Fraze,U.S. patent 3,273,744 (1966).
14. Aluminum Statistical Review for 1999 (Washington, D.C.: The Aluminum Association, Inc., 2000), p. 14.
15. M.B.W. Graham and B.H. Pruitt, R&D for Industry (New York: Cambridge University Press, 1990), pp. 88–89.
16. C.C. Carr, Alcoa, An American Enterprise (New York: Rinehart and Company, 1952), p. 183.
17. K.J. Brondyke and P.D. Hess, “Filtering and Fluxing Processes for Aluminum Alloys,” Transactions AIME (New York: AIME, 1964), p. 1553.
18. J.D. Edwards, F.C. Frary, and Z. Jeffries, in Ref. 4, p. 245.
19. M. B. W. Graham and B. H. Pruitt, R&D for Industry (New York: Cambridge University Press, 1990), pp. 93–96.
20. J.D. Edwards, F.C. Frary, and Z. Jeffries, in Ref. 4, p. 13.
21. D.M. Lewis, Metall. Rev., 6 (22) (1961), pp. 143–192.
22. E.F. Emley, Int. Metall. Rev. (206) (June 1976), p. 102.
23. Papers presented at the Continuous Casting Seminar (Washington, D.C.: Aluminum Association, 1975).
24. Z. Jeffries, “Two Decades of Precipitation Hardening Alloys,” Metals and Alloys, 1 (1) (1929), p. 4.
25.H.Y. Hunsicker and R.C. Lemon U.S. patent 3,161,502 (1964).
26. Designations and Chemical Composition Limits for Aluminum Alloys in the Form of Castings and Ingot (Washington, D.C.: Aluminum Association, 1999 February).
27. J.C. Benedyk, “Automotive Aluminum Casting Trends and Developments,” Light Metal Age, 58 (9–10) (October 2000), pp. 36–41.
28. Aluminum Statistical Review for 1999 (Washington, D.C.: The Aluminum Association, 2000), p. 24.
29. R. Couchman, Alcoa (retired), unpublished work.
30. R.F. Ashton, “The Metallurgy of Press Heat Treatable Al-Zn-Mg Extrusion Alloys” (Paper No. 12, presented at the Int. Extrusion Technol. Seminar, New Orleans, March 3–5, 1969.

Robert E. Sanders, Jr. is with Alcoa, Inc.

For more information, contact R.E. Sanders, Jr., Alcoa Inc., 100 Technical Drive, Alcoa Center, Pennsylvania 15069; (724) 337-2478; fax (724) 337-2044; e-mail robert.sanders@alcoa.com.