Ar4NUAL REVIEW
io
such giant bowls when
led together form a chamber 1 will contain a nuclear reactor Phoebus-2 series rocket enginl?S
AI uminum EARL T. WANDERER
The growing sales of products, plus wider use of aluminum in these products, and the introduction of aluminum in new applications have been the major factors for the period of rapid growth in this industry.
riniary aluminum production in 1966 reached a new
PUnited States record of 2,968,384 short tons, a 7.7% increase (213,906 tons) over the previous record set in
1965. At the end of 1966, primary capacity including incompleted facilities, totaled 3,691,000 short tons. The aluminum industry is in a period of rapid growth influenced by growing sales of products employing aluminum, plus wider use of aluminum in these products, and the introduction of aluminum in new applications. Major developments reported during the past 1 2 months are covered in the following pages.
ALLOY AND TEMPER DEVELOPMENT New thick aluminum alloy 2024-T851 plate has been developed for use in critical aircraft applications. T h e new temper improves short transverse properties of rolled plate sufficiently to meet requirements for preforged and rolled product. Cost savings arc expected to result because of the elimination of the forging operation (24. Tests of casting alloy K01, which is in the R1-Cu-AgMg system, show properties equaling those of alloy 2014 forgings. A report discusses properties at temperatures ranging from -423' to 600' F.; properties of welded assemblies; fatigue impact and shear strength; and static load strength of a landing gear strut ( 3 A ) . Two alloys, X7007 and X2021, are being evaluated by the aerospace industry. I n preliminary tests, the new heat treatable alloys show room temperature strengths 10 to 15% greater than high strength weldable alloys previously developed. They have good weldahility, high weld properties, and in resistance to corrosion and stress corrosion cracking, they compare favorably with other high strength aluminum alloys now in cryogenic service (7A). VOL. 5 9
NO. 8
AUGUST 1 9 6 7
75
FABRICATION AND PROCESSES A new dip brazing process for dissimilar metals has been developed which aerospace users employ for coniplex components. The dip brazed couplings show high strength, good conductivity, and no galvanic corrosion. Dissimilar metal couplings with both cylindrical and flat parts have been produced for use in rocket engines, nuclear power plants, and electronic components (74B). A new method of permanently coloring aluminum, developed as part of the aerospace program, has been modified for commercial applications. T h e process is reported to apply almost any color to the face of aluminum without chipping, fading, or cracking. First successful application was a coating applied to a small Navy satellite (756’). A need has cxisted for a method of analyzing aluminum castings that would give quantitative results for oxide or abrasive inclusioiis, which contribute to poor machinability. A simple acid extraction method, involving successive treatments with hydrochloric, nitric, and hydrofluoric acids, has been developed. T h e method is believed adequate for the determination of such inclusions as a-alumina, silicon carbide, spinel, and particles of high alumina brick (70B). Research involving the use of cryogenics in aluminum welding has indicated that increased tensile properties and reduced porosity in weldments of 5/16-incl?and l / z inch alloy 2014-T6 plate, have resulted lrom shortening the time-temperature cycles and controlling the solidification pattern through the use of liquid carbon dioxide as a chilling agent during welding. The investigation is sponsored by the National Aeronautics and Space Administration to find means of increasing the strengthweight ratio and reliability of weldments in aerospace vehicles. Preliniinary data indicate that it will be possible to improve the tensile properties and rcduce porosity of aluminum welds by refining and supplementing present concepts for controlling the thermal pattern during welding ( I 7B). Heat input to welds is a controlling factor in the penetration, base metal dilution, and final metallurgical structurc of the welds. An experimental design technique has been developed to predict heat input, and less than 4.7% maximum error has been experienced with the method (32B). A method of predicting physical properties in arc welding applicable to any combination of base and electrode metals has been developed. For given values of heat input, three predicting equations will arrive at the most probable physical property values. When combined with the heat input predicting equation, the welding variable values required for a specific property may be obtained prior to the stare of the weld. The compatibility of the physical properties with welding specifications may also be determined by the three property predicting equations (33B). A new process that achieves a breakthrough in die casting quality has been announced. I t produces aluminum parts that are dense, strong, pressure tight, weldable, and 76
INDUSTRIAL A N D ENGINEERING CHEMISTRY
heat treatable. Made available without licensing fees or other remuneration to die casting machi ne builders and die casters, the process reportedly will niultiply the use of aluminum die castings in all industries (76B). The development of specialized alloys, tempers, and techniques has refined the art of hand forging to the point where it now can produce a broad range of shapes that cannot economically be made by any other process. Hand forging is often an appropriate method of producing prototypes or small quantities of forged parts (17B). Described as a relatively new painting process, electrocoating deposits a dense, uniform layer of paint on edges, flats, and corners of complex; extruded shapes. Compared to electrostatic spray methods, electrocoating has lowered costs and improved the finishing of intricate contours and recesses in extrusions ( 78B), Results of a program investigating the adhesive bonding of die castings indicate that the joining method will be used extensively. Considerable resistance exists because of insufficient experience in service data, but it is ideal for parts that are difficult to weld. Adhesive bonding of aluminum die castings to produce engine cylinder heads was not recommended, however, because of loss of strength encountered with water. Although the deleterious effects of water can be inhibited, uncertainty exists concerning performance after 10 years of service in water a t about 24OOF. (79B). Much of the success in utilizing aluminum for sophisticated new products of the future will depend on the ability to join them under a variety of new conditions. Welding in the near future is heading more and more toward automation, instrumentation, and feedback controls as engineers seek greater economy, more reliability, and higher quality welds. Promising new joining methods include electron beam, laser welding, pressure welding, and adhesive bonding @OB). A U.S. Navy aluminuni torpedo component, designated a NAVOL tank, is a cylindrical pressure vessel approximately 21 in. in diameter and 26 in. long. I t is used for the storage of hydrogen pcroxide. A research program has indicated that the production welding of NAVOL tanks by the electron beam method is definitely feasible and economically attractive. The electron beam welded tank proved to be leak-tight under hydrostatic testing of 3000 p.s.i. Die penetrant inspection revealed that the welds were of high quality (9B). Two classes of solid-state welding can be defined on the basis of the amount of deformation used during joining. Deformation welding relies essentially on gross plastic deformation to create welds. During diffusion welding, the second class of solid-state welding, deformation occurs only on a microscale, and diffusion is the principal factor in weld formation. For both types, clean metal surfaces are placed in close contact under pressure for a length of
AUTHOR
E. T . Mianderer is Development Manager, itlachin-
e r j and Equipment Section, A@plications Engineering, for Alumi-
num Co. ojf America. M r . Wanderer authored lastyear‘s review; engineersjrom Alcoa hane authored this r e v i m since 1961.
time a t a desired temperature. A study of solid-state welding of aluminum concludes that sound weld formation is promoted by careful surface preparation ; welding temperature has a pronounced influence on the formation of strong welds; welding in a protective environment is helpful because clean aluminum surface can be kept from excessively oxidizing at elevated temperatures ; intermediate foil layers of copper or copper-silver eutectic alloy can be employed to join aluminum quickly at 900' F.and with little welding deformation (7B). A new roll-forming mill that can produce up to 200 different open shapes, round tubes, and special close shapes, with a single combination set of forming rolls has been developed. T h e new mill can process aluminum up to l / 4 in. thick (20B). A new specially engineered system for welding with fine aluminum wires that eliminates burn backs and cobbles has been reported. The welding gun has a goose neck design and a self-contained air driven motor that pulls wire through the feed conduit instead of pushing it. The system is designed for wires from 0.030 through 0.045 in. in diameter (27B). Major jet aircraft components arrive in Seattle, Wash., in a specially designed aluminum gondola car. The car is 90 ft. long, nearly twice as wide as conventional gondolas, and weighs only 48.2 tons. It is used to haul long, extruded aircraft spar caps (22B). T h e newest developments in weldable aluminum alloys are the copper free, heat treatable, aluminum-zincmagnesium alloys which include X7004, X7005, and 7039. Weldments in these alloys exhibit tensile properties 20% higher, and parent metal properties up to 35'% higher, than high strength commercially available 5000 series alloys. The new alloys also have good ductility and formability. High tensile properties in the heat treatable alloys are obtained by solution heat treatment and natural or artificial aging. Similarly, the heat affected zones in new 7000 series weldments naturally age to high strengths in the as-welded condition. With continuing alloy improvement, and extensive application of such exotic processes as electron beam, laser, and pressure methods, aluminum's welding horizon will continue to broaden (23B). Duplex aging cycles are reported to impart significant resistance to stress corrosion in the 7000 series alloys. Although the treatment lowers mechanical properties from the heat treated (T6) condition, it permits use of materials at higher stress levels in applications subject to stress corrosion. Duplex aging cycles consist of a low temperature aging followed by higher temperature aging, each for a carefully controlled period (37B). The tear resistance and notch toughness of welds of various aluminum alloys are generally greater than those of cold worked or heat treated base metal, and approach those of annealed base metal. Except for the 7000 series alloys, there is no significant decrease in the toughness of welds between room temperature and -320" or -423' F. Excluding filler metal alloy 4043, used with alloy 6061, the toughness of the weld is equal to or greater than that of the base metal (2723).
A quantitative study has been made concerning the effects of applied magnetic fields on welding arcs to produce improved quality welds a t higher speeds. Applying an optimum magnetic field provides a possibility of greater flexibility in welding techniques at increased speeds on magnetic and nonmagnetic materials (8B). A research program, conducted to investigate potential methods for joining alloy 2219 tubing to Type 321 stainless tubing, revealed that diffusion welding is the best method for joining the dissimilar metal tubing (3B). Boring sequence, internal quenching fixtures, racking position, vent tubes, and quench rate are factors that should be considered to control residual stresses when heat treating hollow cylindrical aluminum forgings. Residual quenching stresses can affect such characteristics of forgings as machining distortion, fatigue life, and resistance to stress corrosion cracking ( I B ) . Composition of the aluminum alloy influences characteristics of the anodized coating. Allowances must be made in the design stage for dimensional changes in close tolerance parts to be anodized. Preferred solutions and conditions for conventional and hard coatings are presented in a report of modern practices for anodizing and sealing aluminum (ZB). Hot pressing 2024 alloy aluminum sheet and NS-355 stainless steel wire produces a composite plate which exhibits tensile strength exceeding 170,000 p.s.i. The material was developed to meet NASA-established properties of 175,000-psi. minimum tensile strength a t room temperature, and 0.144 lb. per cu. in. or less in density. Aluminum was specified as the matrix and continuous steel wires (0.010 in. or less in diameter) were stipulated as the reinforcement. The composite plate can be produced in commercial quantities (4B). A new filtering process permits the use of emulsions employed as lubricant-coolants in aluminum rolling mills to be extended indefinitely. Previously, emulsions deteriorated and had to be replaced as often as every 4 to 6 weeks. The process has been used for approxirnately 3 years on production equipment rolling aluminum, and the emulsion has never been replaced, except for replenishment to cover normal losses (24B). A new machine has been introduced that forms threepiece aluminum can bodies with ultrasonically welded lap joints. The containers can be up to 5 in. in height, with diameters ranging from 211/16 to 4l/l6 in. Beer and soft drink can makers are the primary prospects for the new unit. T h e machine fits into existing tinplate lines, and has a production speed within the range of economic practicability (25B). The increasing use of aluminum in the transportation, marine, communications, and building products industries requires the metal to withstand a variety of severe environments. A multiduty coating has been developed which provides long term protection from severe corrosive environments without affecting appearance; seals and primes for decorative finishes that may require optimum adhesion; and can be applied with simple, low cost methods. The coating is a silicone-type resin selected after 8 years of field testing (26B). VOL. 5 9
NO. 8
AUGUST 1967
77
T o produce high quality resistance welds in aluminum, a butyl sealant applied immediately after chemical cleaning eliminates the formation of passive films. The sealant is dissolved in the joint area just prior to the welding operation, and electrode pressure forces the butyl out of the work area, exposing clean, faying surfaces to each other (3423). A low cost substitute for alloy 6061-T4 for stretch-formins promises to broaden application of the technique. The new alloy is a tempered form of alloy 5052 that is sufficiently ductile for sheet forming without sacrifice of strength. It matches the 40,000-p.s.i. yield strength of 6061-T4, and has a faster work-hardening rate (28B). New custom mold casting techniques are reported to produce precision a h m i n u m castings up to 14 times the weight now practical for conventional processes. Better tolerances and up to 30y0 better smoothness in as-cast surface finishes are said to result. Success of the new method comes chiefly from heat control at the mold curing stage (29B). The functional requirements and appearance are primary design considerations for aluminum castings. Equally important is the selection of the casting process that can fulfill both needs. ,4report relates casting design to the characteristics and capabilities of the principal aluminum casting processes (72B). With the development of new adhesives, adhesive bonding of aluminum to itself and to other metals and nonmetals has become common practice. Choosing the right adhesive for a particular application requires careful analysis of many factors that affect the bond during service life. A report on structural and nonstructural adhesives gives guiding comments on strength, environmental capabilities, compatibility with other metals, costs, and other characteristics that must be considered in specifying adhesives for a bonding systems (5B). An extensive report describes the welding characteristics of high strength aluminum alloys and the effects of welding on tensile and fatigue properties, notch sensitivity, and stress corrosion resistance (6B). Success or failure of finishing treatments for aluminum, including anodizing, depends largely on the preparatory cleaning and conditioning operations. A report on modern practices for cleaning and brightening aluminum describes chemical cleaning, etching, and chemical and electrochemical brightening procedures employed to prepare surfaces for anodizing or other finishing treatments (73B).
A PP L C C A T I0 NS A new aluminum hulled research subniarine is being readied for sea trials in California. Approximately 7200 lb. of alloy 5083 sheet, plate, and extrusions are employed for fabricating and welding the vessel hull. Aluiiiinuni was selected because of its light weight, strength, and good corrosion resistance. T h e submarine will be able to operate at depths of 6000 ft. for up to 1 2 hr. ( 5 2 ) . Aluminum structural members are the basic framework components for new buildings engineered to house 78
INDUSTRIAL A N D ENGINEERING CHEMISTRY
military personnel and materials in the field. Shelters measure 100 ft. long, by 75 ft. wide, and 30 ft. high. They are assembled and erected from the ground without a crane, gin-pole, or special tools. The aluminum frame is capable of withstanding winds of 80 m.p.11. and snow loads of 20 lb. per sq. ft. The shelter can be erected in 72 hr. by a military crew of 20 men (6C). A new automobile radiator design employs thin wall aluminuni tube which helps reduce unit weight to less than half that of a copper radiator. The thin wall tube reduces brazed joint area by 7553 o\rer a previous alurninum radiator. Reliability is said to be improved, which simplifies the dip brazing process (7C). Experience with 150,000 units has proved the reliability of aluminum radiators. All that remains before high production radiators switch from copper and brass to aluminum is the development of inexpensive, reliable fabrication methods. Dip brazing, furnace soldering, and furnace brazing show the most promise ( I C ) . T o build a Lunar Xfodulc having the highest reliability and lowest possible weight, engineers used complex forged and machined parts to eliminate bulky weld joints. The crew cabin was closed with an epoxy sealed riveted joint where machine welding was not possible, and aluminum sheet and stainless steel tubing were chernically milled to minimize \veiglit. The descent and ascent stages of the Lunar Module are constructed almost entirely of aluminum alloys 7079, 7075, 7178, 2219, and 2024 (76C). Aluminum is considered fa1,orably in bridge construction because of its light weight and corrosion resistance. These make possible reduction of dead load prefabrication of large units, thus reducing manufacturing costs ; reduction in cost and size of foundation; total or partial elimination of costly concrete false work; and reduced painting requirements. The use of aluminum in bridge construction will be advanced by designs based on properties of plate and extrusions, arid the application of improved cost analysis (8C). The emergence of “environmental control’’ in architecture has resulted in builders specifying more and bigger lighting fixtures. Concurrently, architects are placing increasing emphasis on design and appearance of lighting equipment. Aluminum is the beneficiary of these trends because of its fabricating ease and good finishing characteristics, good thermal conductivity, design versatility, corrosion resistance, and light weight (9C). A major home builder is experimenting with extruded aluminum framing to replace wood studs, joists, and trusses. A prototype ranch home has been built with light metal shapes contributed by members of T h e Aluminum Association. Fewer framing members are required compared to wood, and the aluminum extrusions achieve savings by performing a number of functions such as doubling as door and window frames, corner posts, and trim. An average 2000-sq.-ft. house would utilize approximately 2 tons of aluminum framing (7OC). A huge 7800-lb. aluminum casting will be machined, plated, and polished-a year long task-to form a 100-in. diameter mirror. I t will be used to test components re-
quired for a new 150-in. telescope to be installed a t the Kitt Peak National Observatory (3C). Aluminum applications are expanding in air conditioning and refrigeration products. Considerable knowledge of the light metal’s performance and processing techniques in such products as compressor parts, fins, and all-aluminum coils has been collected in recent years. A report summarizes the fabricating and joining methods employed in processing aluminum tube for air conditioning and refrigeration products (2C). Transportation is seen supplanting construction as aluminum’s biggest customer. Added market impetus comes from railroads and mass transit systems, the marine industry, and a rising demand for aluminum in the automotive industry. Designers of high speed trains today are specifying aluminum, and government supported projects have begun in recent months to call for more high speed trains (77C). Two aluminum applications in a low rise commercial building a t Pittsburgh’s Allegheny Center may foretell construction trends. Extruded H-shaped franie supports, 34 ft. high, are the tallest load bearing aluminum columns yet employed. T h e extrusions also serve as window stops, and exterior and interior decoration. They frame the structure’s 9- X 20-ft. windows a n d the aluminum-polystyrene-aluminum sandwich panels that comprise much of the exterior ( 7 I C ) . A unique use of aluminum spandrels distinguishes a new, low rise office building in Richmond, Va. Each floor of the circular concrete and steel structure is wrapped in a 700-ft. long, 9-ft. wide, continuous length of 0.032-in. aluminum sheet. As the sheet was attached, it was hammered into a free-form textured pattern by the architect. T h e resulting aesthetic and functional wrinkles impart a n unforgettable impression to viewers (72C). A simulated ride through outer space and a plunge into a volcano are available to visitors a t Expo 67. T h e unique amusement ride is a 215-ft. high weblike structure built of 245 tons of aluminum tube and bonded aluminum panels (73C). A complex valve body is forged from a heavy extruded aluminum slab to meet light weight and gastight requirements for a respirator application. T h e unit handles various mixtures of air and oxygen, and the valve body must be dense and completely gastight (78C). T h e Phoebus-2 nuclear rocket, test fired in Nevada, employed a n aluminum pressure vessel made of two giant bowl shaped forgings to house the reactor and receive the rocket engine nozzle (42). T h e feasibility of aluminum tubing for seawater conversion equipment will be demonstrated by a pilot desalination plant, built and operated under a U.S. Department of Interior research contract. T h e plant will be constructed a t Wrightsville Beach, N.C., and will have a daily capacity for converting 50,000 gal. of seawater into drinkable water (74C). A new aluminum roofing and siding system has been developed which makes possible attractive, weathertight industrial buildings while affecting savings on construction and handling expenses. T h e panels are available in
lengths limited only by shipping considerations, and are attached with concealed fasteners. T h e panels are flat on the underside and ridged on top, with high standing seams a t each edge. Adjacent seams fit together, enclosing anchar clips fastened to the super structure. Seams are clamped and locked by a special electrically powered closure tool. T h e construction provides good strength over long, unsupported spans and enables builders to reduce structural supports (75C). As interest in the seas quickens, research programs are under way to expand aluminum undersea technology and antisubmarine warfare. Programs involve providing engineering assistance to pioneering individuals and organizations, and developing and fabricating underwater aluminum components and structures (79C). REFERENCES Alloy and Temper Development (1A) Design News 22 (7), 31 (1967). (2A) M o d . Metals 22 ( l l ) , 92 (1966). (3A) Ibid.,23 (l), 48, 52 (1967). Fabrication and Processes (1B) Barker, R. S., Turnhull, G. K., M e l d Progr. 90 (51, 60, 65 (1966). (2B) Ibid. (61, pp. 68, 75. (3B) Crane, C. H., Lovell, D. T., Baginski, W. A., Olsen, M. G., Welding J . 46 ( l ) , 2 3 4 , 31-S (1967). (4B) Davis, L. W., Metal Progr. 91 (4), 105, 114 (1967). (5B) Earnest, S. A., Hovland, L. W., Minford, J. D., Machine Deszgn (2), 192, 200. (6B) Evans, R. M., Maykuth, D. J., Mafer. Design Eng. 65 (31, 74, 79 (1967). (7B) Hauser, D., Kramer, P. A., Dedrick, J. H., Welding J . 46 (2), 11-S-20-S (1 967). (8B) Hicken, G. K., Jackson, C. E.,Ibid.,46 ( l l ) , 5 1 5 3 , 5 2 4 3 (1766). (9B) Hinrichs, J. F., Ramsey, P. W., Ibid. ( l ) , pp. 39, 46. (10B) Light Metal Age 24 (11, 121, 9, 10 (1966). (11B) Ibid. (7, 81, pp. 15, 18. (12B) Machine Design 39 (9), 155, 163 (1967). (13B) Metal Progr. 90 (51, 96, 100 (1966). (14B) Mod. Metals 22 (4), 41, 42 (1966). (15B) Ibid., p. 96. (16B) Ibid. ( 8 ) , 39, 47. (17B) Ibid. (9), pp. 68, 74. (18B) Zbid. p. 46. (19B) Ibid. (lo), pp. 64, 71. (20B) Ibid.,p. 92. (21B) Ibid. ( l l ) , p. 83. (22B) Zbid.,p . 92. (23B) Ibid., 23 (l), 155, 158 (1967). (24B) Ibid. (2), p. 95. (25B) Ibid., p. 72. (2GB) Ibid.,pp. 33, 35. (27B) Nelson, F. G., Kaufmann, J. G., Holt, M., Welding J . 45 (7), 321-S, 329-S (1966). (28B) Prod. Eng. 38 (2), 78 (1967). (29B) Ibid. (9), p. 115. (30B) Ready, T. J., Jr., Welding J . 46 (21, 107-16 (1967). (31B) Rotsell, W. C., Long, J. R., MetalProgr. 91 (5), 106, 109 (1967). (32B) Stegner, D. A . J., Wu, S. M., Braton, N.R., Welding J . 46 (3), 128-S (1967). (33B) Ibid. pp. 129-S, 1 3 2 4 . (34B) Wallis, L., Metal Progr. 91 (41, 72, 74 (1967). Applications
(1C) Dickers-, P. D., Weltman, W.C., Metal Progr. 90 (41, 195, 202 (1966). (ZC) Haygood, A. J., Earnest, S. A., Metal Prod. Mjg. 23 (121, 72, 75 (1966). (3C) Light Metal Age 25 (1, 2), 40 (1967). (4C) Machinery 73 (91, 114 (1967). (5C) Mod. Metals 2 2 (41, 106 (1966). (GC) Ibid.,p. 102. (7C) Ibid., pp. 33, 39. (8C) Ibid. (91, pp. 60, 66. (9C) Ibid., pp. 28, 42. (1OC) Ibid. .(12), 102 (1967). (11C) Ibid., p. 104. (12C) Ibid., 23 (l), 94 (1967). (13’2) IFd. (21, p. 101. (14C) Ibid. ( Z ) , pp. 96, 96. (1SC) Ibid.,pp. 53, 54. (IGC) Orrok, N. E., Metal Progr. 91 (41, 195, 202 (1967). (17C) Prod. Eng. 37 (261, 90 (1966). (18C) Ibid., 38 (6), 107 (1967). (1%) Undersea Tech. 8 (4), 20, 21 (1967).
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NO. 8
AUGUST
1967
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