annual review
B. WYMA
Aluminum New alloys with improved corrosion and abrasion resistance, new production
and fabrication
techniques, and new manufacturing equipment are k q aspects o f Progress in aluminum technology rimary aluminum production in 1964 reached a new
Precord total of 2,552,971 short tons, a n increase of 240,441 short tons over the record set in 1963. At the end of 1964, primary capacity, counting that of uncompleted facilities, reached 2,868,600 short tons. New facilities include Intalco’s aluminum reduction plant at Bellingham, Wash., a joint venture of American Metal Climax, Pechiney Enterprises, and Howe Sound. I t will have the world’s largest capacity potline, a unit capable of producing 76,000 short tons annually. T h e constantly expanding use of aluminum in major market areas reflects the impact of new products, processes, and applications. Also indicated is a new annual production record in 1965. Major developments reported in the literature during the past 24 months are covered here. Alloy Development
A number of new alloys have been introduced to establish and further improve aluminum’s performance in applications in the nation’s industries. Alloy X5015 is a specialized sheet alloy, characterized by a high degree of brightness and clarity, developed for automotive trim components. The nonheat-treatable composition exhibits mechanical properties and forming characteristics suitable for interior and exterior trim components produced through standard manufacturing operations and finishing techniques ( 3 A ) . Alloy X8081, a new aluminum alloy containing 20% tin, was introduced in coiled sheet form for mass production of steel-backed aluminum bearings. Displaying good corrosion resistance properties, the new bearing material meets a need fostered by the . automotive industry concept of building reliability in passenger car and truck engines ( I A ) .
Anoclad A13 sheet, a new grade of aluminum sheet whose alloying elements produce a stable black when processed to obtain the Duranodic 3358 finish, has been introduced for architectural applications. The hard, dense surface that results provides good resistance to corrosion and abrasion and imparts wear resistance equal to hardened steel and chrome plate. I t is well suited for architectural exposures that are difficult to maintain (24). Number 7 porcelain enameling sheet is a clad product consisting of a heat-treatable alloy core and a specially selected cladding alloy containing elements that at most are only slightly reactive to molten frits. As the sheet cools following the porcelain enameling operation, the core alloy develops high mechanical properties equal to the demands of most applications where strength is a prime requirement. T h e cladding alloy provides good coverage and color clarity with one-coat systems ( 4 A ) . Production
Electrolytic smelting dominates the aluminum industry because it produces economically a quality product, not because research and experience with direct reductioncarbothermic-techniques are lacking. Research and semicommercial pilot-scale testing of methods have been conducted since Hall and Heroult invented their processes in the late 1800’s. The electrolytic process has been employed exclusively and will be employed exclusively far into the future ( I B ) . Fabrication and Equipment
T h e direct chill method of casting aluminum rolling, forging, and extrusion ingots allows high production rates on a continuous or semicontinuous basis. Grain structure and ingredient dispersion are improved by direct chill casting, but addition of suitable master alloys results in improvement by refining the grain of the aluminum alloy. Grain refining increases casting speed, reduces cracking, reduces cold shuts, increases pressure soundness, and reduces segregation. T h e structure of solid aluminum depends upon the rate of nucleation of crystals, which is influenced by the VOL. 5 7
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presence of transition metals such as titanium, columbium, and zirconium. Laboratory investigation and production experience have shown that the amount of grain refiner required to produce an equiaxed structure is considerably less than the amount traditionally used (ZC). A 9-ton roll-forming machine and related equipment mounted on lowboy trailers produced pleated aluminum wall panels for the Houston, Tex., domed stadium right at the job site. The 2100-ft. stadium circumference required 207 panels 66 ft. long and 430 panels over 22 ft. long. A 5-man crew fabricated some 60,000 lb. of prepainted charcoal gray, stucco embossed aluminum coils in less than 10 working days. The decision to take the mill to the construction site was based on a study of shipping and handling costs involved in the massive project (i’ZC). A major method of imparting surface designs to aluminum is rotary embossing, in which hardened steel rolls imprint patterns a t high speeds. Sheet may be decorated with multiple finishes-for example, certain areas may be engraved with a fine stipple or screen effect, while adjacent areas are left clear or embossed in different planes. The basic decorative effects achieved by embossing are a three-dimensional plane and contrasting light reflectivity. Three types of embossed designs are used for metal surface texturing : over-all, localized, and register (QC). Casting light metal components is one of the most versatile production methods available to industry, and a relatively new technique known as premium quality casting now adds the advantage of reproducible mechanical properties approaching those of wrought products. Premium quality castings are distinguished from conventional quality castings by being specifically engineered to exhibit predetermined high mechanical properties in specific areas of the castings. They are made to the same precision and complexity as conventional castings and embody the best of the founder’s art. Premium quality castings produced for the aerospace industry are large and complex and in alloy A357 they exhibit properties of 50,000 p.s.i. tensile; 40,000 p.s.i. yield; and 5YGelongation (5C). Increased productivity of aluminum strip has resulted from the use of a new continuous casting line that produces sound sheet in a wide range of alloys including heat-treatable alloys. The new line casts sheet u p to 24 in. wide at speeds from 6’/2 to 8 ft. per min. T h e facility is completely integrated and includes two gas fired melting furnaces, a holding furnace, four two-high mill stands to roll the strip to size, and heating furnaces between the stands to maintain rolling temperatures. The new continuous casting line is designed on a traveling mold principle and is reported to be the widest machine of its type in operation (3C). Highly accurate electroforming of aluminum optical components has been accomplished under sponsorship of the National Aeronautics and Space Administration’s Langley Research Center, Hampton, Va. T h e method produced nonmagnetic solar energy concentrators for 86
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space applications, but its success is regarded as having a far-reaching impact on aluminum electroforming technology. A well established precision process for many other metals, electroforming produces a part by electrodeposition of metal on a master or mandrel. Removal of the mandrel leaves an article of the desired shape. The process is best used for parts having intricate internal design, extremely thin walls, or high precision requirements for dimensions and finish (TIC). The important qualities of aluminum sheet products which are coated and lithographed for container applications include the influence of the new -H13 temper, basic characteristics of aluminum and its reactions to the rolling process, and the advantages of the various aluminum alloys employed in commercial packaging operations (16C). Dry annealing thin aluminum foil in coil form often results in objectionable characteristics such as resistance to free unwinding, dry foil edges but oil-slick centers, and stained or discolored foil surfaces. A research program has determined the temperature and atmosphere combination needed to produce free-unwinding coils of foil with a dry, printable surface (77C). A new press designed to hydroform aluminum has been introduced to satisfy the growing use of the metal in the automotive, appliance, and lighting industries. Blanks ranging from 8 to 25 in. in diameter can be handled, and maximum draw depths range from 5 to 12 in. The high production presses operate at a rate of from 1250 to 1800 cycles per hour (15C). A continuous horizontal heat-treating process for aluminum strip has been developed that supports the product on a cushion of air, removing the need for rollers, runners, or other mechanical supports. The new method eliminates surface marks caused by mechanical supports, does away with water- and oil-staining possibilities, and removes length restrictions (TOG‘). Aluminum parts are being produced on roll-forming machines equipped with one steel roll and one rubber roll. The method has proved to be more economical, faster, and more accurate than those used previously, and is capable of turning out 600 parts an hour compared to 250 pieces per hour with conventional dies (14C). A major research center will be built in Pleasanton, Calif., by Kaiser Aluminum & Chemical Corp. to consolidate all of the firm’s present research facilities ( 7 0 . Use of a new process allows continuous rolling of aluminum sheet from finely divided powder in one pass through a rolling mill at rates exceeding 200 ft./min. The sheet is fully densified and metallurgically bonded and does not require subsequent sintering steps. The method is identified as the compacted sheet process, and is reported to eliminate the need for such high capital investment equipment as casting and scalping units, large reversing breakdown mills, and expensive soaking pits (13C). Further development of a patented technique to form aluminum containers by blowing molten metal into a die will examine the possible uses for battery cases, cartridges, and lamp bulb sockets (6C).
How aluminum alloys resist exposure and when to specify conversion, anodic, metal, paint, plastic, and porcelain coatings are important considerations in almost all applications. When and how to select finishes for aluminum must be considered carefully to provide protection, maintain appearances, increase electrical conductivity, or increase resistance to erosion, corrosion, or abrasion (19C). When stress at a particular location in a part is high enough and applied often enough, a minute crack appears and gradually propagates during succeeding cycles until the part ruptures completely even when nominal stresses are safely under the elastic strength of the material. Under repeated stresses, aluminum alloys generally behave like other common metals, but with several noteworthy differences. The stress US. number of cycles (5’-N) curves for many steels show a sharp break around 1 million cycles, after which the stress levels off; 10 million cycles of stress are enough to define their fatigue limits. With aluminum alloys there seldom is any sharp break in the S-N curve; it does not level off until about 500 million cycles (18C). Welding is a fast, economical way to join aluminum assemblies, but various aluminum alloys react differently to the welding process. The choice of welding method and filler metal depends on the base alloys and service requirements for the welded joints. Welding methods, the effect of nonheat-treatable and heat-treatable alloys on welds, filler metal, dissimilar alloys, and dissimilar metals are all factors that must be evaluated to arrive at sound welds ( I C ) . A recent significant development for the aerospace industry was the -T73 temper for alloy 7075 products. T o prove that an item of 7075 material meets the capability of 7075-T73 alloy products, a stress-corrosion cracking stipulation has been incorporated in the military specifications. A 30-day exposure to 3l/2% sodium chloride solution by alternate immersion is now specified, but because the test is lengthy a rapid screening criterion would be valuable. Two such methods have been devised and evaluated; a solution potential procedure and an electrical conductivity method which indicates within a matter of hours whether an item meets the quality for 7075-T73 material (8C). Aluminum brazing differs from welding in that specifically developed fluxes and filler materials, with melting points below those of the alloys being joined, are used for making the joints without melting the parent material. It differs from other brazing processes in that the filler alloys are aluminurn alloys rather than dissimilar metals. This is beneficial from the standpoint of corrosion resistance, strength, appearance, and electroplating operations. Aluminum can be torch-brazed, furnace-brazed, or dip-brazed (4C).
AUTHOR Bruce H. Wyma is Application Engineer f o r the Aluminum Company of America. He has authored ItYEC’s annual review of Aluminum since 1961.
Applications
Corrosion imposes a major expense upon the fertilizer manufacturing industry. The use of aluminum for plant construction can reduce or eliminate the high cost of protection often incurred when other common materials are used. Aluminum is used extensively in fertilizer plants for prilling towers, storage tanks, architectural products, and electrical equipment ( 1 6 0 ) . The largest seamless aluminum tubes ever produced will store gaseous helium at pressures up to 3000 p.s.i. while riding immersed in the liquid oxygen tanks (temperature, - 297” F.) of Saturn V boosters, the nation’s most powerful rockets. Each cylinder is 21.6 in. in diameter, 18.5 ft. long, and weighs 2320 lb. ( 1 0 ) . The first complete Saturn I launch vehicle-1 6 stories of aluminum-placed an 18.8-ton satellite in orbit to climax its maiden flight. Approximately 30 tons of aluminum were required to construct the 164-ft, twostage vehicle; the metal was selected for its strength, light weight, and ability to resist becoming brittle at - 423 F.-liquid hydrogen temperature-and below (100). Aluminum forgings constitute integral parts of instant liquid rocket engines that are fabricated, fueled, and then stowed until needed to power U. S. Navy Bullpup A missiles. Two forged parts are welded together to form two compartments in which approximately 106 lb. of liquid propellant are stored. Packaged power plants solve a major missile problem by making Bullpups available on almost immediate notice ( 6 0 ) . Constructed to an unprecedented degree of accuracy, a 120-ft. diameter aluminum saucer installed on Haystack Hill near Tyngsboro, Mass., is considered the free world’s most advanced communications instrument of its kind. I t will be operated for the U. S. Air Force by Massachusetts Institute of Technology. Approximately 350,000 lb. of aluminum were required to build the big dish and its protective radome. First assignment of the research tool is to expand communications experiments being conducted by 60-ft. diameter antennas aimed toward a belt of copper space fibers placed in orbit by the United States (150). A major development in construction of foil-fiber containers makes composite cans stronger and less vulnerable to moisture leakage. A dry-bonding method eliminates the need for animal-based glues or emulsion adhesives for bonding spiral wound containers. T h e cans hold dry products under moderate vacuums and liquid products under moderate pressures and attain acceptable performance levels during various storage periods ( 1 2 0 ) . Packed like circus midgets who emerge unendingly from a compact car, 200 miles of aluminum tube crammed into a shell less than 100 ft. long now are wringing helium from natural gas. The 6l/%-ft.diameter tube-inshell aluminum structure is regarded as the world’s largest cryogenic heat exchanger. It is the first commercial application of aluminum tube in a wound heat exchanger, Aluminum was selected over copper and stainless steel because it slashes weight from 155 tons to VOL. 5 7
NO. 8
AUGUST 1965
87
5 5 tons. Tubing was supplied in alloy 3003 with a wall thickness of 0.032 in. (9D). A military veh.icle with hull structure contours more typical of sports cars than thundering- tanks has resulted from the use of forged aluminum armor rather than conventional aluminum armor plate. Rakish curves are achieved by use of large, heat-treated forged aluminum armor components employed in key areas of armored vehicle hulls (80). A unique process development permits production of a wider range of Duranodic 300 architectural aluminurn finishes ranging from light bronze to black on the same extrusion alloy. Previously, one aluminurn alloy was used to produce the black finish and another to achieve the light, medium, and dark bronze shades. The new technique aids fabricators by reducing their special alloy inventories required for Duranodic finishes ( 7 70). Huge aluminum forgings form vital parts for the Air Force/Kavy F-111 supersonic jet aircraft, the nation’s newest fighter plane. Fabricated in alloy 7073, the 467-lb. die forgings help form the aircraft’s main landing gear ( 4 0 ) . A 500-car order for 100-ton aluminum covered hopper cars, the largest cars ever built, will require more than 10,000,000 lb. of aluminuiri for construction. Light weight of the cars is estimated at 55,700 lb., giving the huge hoppers a carrying. capacity of 207,300 lb. (140). Advanced manufacturing techniques now produce coiled aluminum tube with a special aluminum alloy external cladding that protects the core while carrying a variety of liquids and gases in corrosive industrial atmospheres. If pitting attack occurs, the cladding corrodes preferentially-spreading laterally, not inwardly--leaving the alloy 5050 core intact and functioning efficiently. The tube is available in sizes ranging froin an outside diameter of 0.125 in. and wall thickness of 0.025 in., to an outside diameter of 0.0750 in. and wall thickness of 0.058 in. (13D). A prototype aircraft built to take off straight up, cruise in a conventional manner, and land gently straight down has been unveiled for the Navy. Designated the X-22A, the essentially all-aluminum craft employs alloy 7079-T6 hand forgings for key structural members (70). Chemical carriers and transportation equipment makers are stepping up efforts to save on equipment weight and thus increase payloads. Two dry-bulk aluminurn truck trailers have been completed which will be used in shipping anhydrous sodium thiosulfate. The railroads have under consideration construction of a 20,000-gal. aluminum pressure car for handling anhydrous ammonia ( 2 0 ) . As a group, aluminum-base materials are used for their lightness and strength, corrosion resistance, thermal and electrical conductivity, heat and light reflectivity, and hygienic and nontoxic qualities. These qualities were taken into account in the design of the largest allaluminum barge ever built, which was launched recently at Avondale Shipyards, New Orleans, La. The craft has a hull 195 ft. long, 52 ft. 6 in, wide, and 12 ft. 7.5 in. deep of double skin construction. I t contains 88
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
six individual compartments and will be used to transport a variety of chemical products on inland waterways. Barge construction accounts for use of more than 400,000 lb. of aluminum. Because of the light weight of aluminum barges, they will carry 14y0more cargo at the same draft (8.5 in.) as similar barges constructed of steel. The rated capacity of the new barge at that draft is 2264 tons (30). Aluminurn and its alloys are ideal as materials of construction in many environments because of their general atmospheric corrosion resistance. However, strong alkalies will remove the tenacious aluminum oxides which contribute to this corrosion resistance. However, in wine environments normally considered unsuitable fur aluminum because of such alkalies, actual experience has established aluminum as an excellent material of construction with many years of successful application (50). Large aluminum tanks for polyethylene storage are fabricated of corrosion-resistant plate. Nine such units of record size for shop-fabricated tanks are now in operation. The tanks were installed as complete packages at the job site. Polyethylene may be stored in aluminum tanks without risk of discoloration caused by products of corrosion. BIBLIOGRAPHY Alloy Development (1A) (2A) (3.4) (4A)
J . .tfe!als 17, 460 (i965). M e c h . Eng. 87, 76 (1965). Metal Progr. 83, 8 (1965). Wallace, P. F.: Wagner, K. H., .Meid Prod.
.Wantif.
72, 113 (11165)
Production (1B) Stroup, P. T., Trans. A I M E 230, 356, 371 (1964) Fabrication a n d Equipment (1C) Collins, I?. R., M a c h i n e Design 128, 133 (1965). (2C) Crouch, C . H.. hlanck, J. G., Hoff, J. C., .tlod. J f e t o l r 20, (3), 56, 59 (1965). (3C) Dauqherty, T. S., J. Metals 16, 827, 830 (1964). (4C) Dickerson, P. B., .Metal Progr. 83, 73, 78 (1965). (5C) ller, A . J., .Mod. Metals 19 (12): 44, 48 (1964). (6C) J. .bfetals 16, 547 (1964). (7C) Zbid., 17, 33b (1965). (812) King, IC-.,Lifka, B. i V , , Willey, L..4., .%fu!er. E d . 89, 95 (1965). (9C) Lewis, H. M., .Mod. M e t a l s 20 ( l ) , 58, 60 (1965). (1OC) Light Metal Age 21 (12). 20 (1963). (1lC) Zbid., 22, (8), 4: 5 (i964). ( i 2 C ) Ibid.:( i 2 ) , p . 9. (13C) )>fad .IfZ!GlT 19 (2;: 11, 22 (1964). (14C) Z6id., ( l o ) , p . 62. (1j C ) Zbid., 20 ( 3 ) , 20, 32 (1965). (16C) Peak, B. N., Light ,44etd Aqe 2 2 ( 2 ) . 6 , 8 (1965). (17C) Robinson, G. C., .Mod. M r t n l s 20 (2), 76, 79 (1965). (18C) Stickley. G. W., Lyst, J. O., Prod. Eng. 35 ( l l ) , 71, 78 (1964). (1OC) Vanden Berg, R. V., Ibid., (2), p p . 65, 80. Applications (1D) A~iationWeek S’pace Technol. 80, 95 (April 6, 1964). (2D) Chem. Eng. News 42, 25 (Feb. 10, 1964). (3D) Corrosion Prevent. Control 11, 15 (1964). (4D) Desipn News (Dec. 21: 1964). (5D) Gleekman, L. \V,, Chem. Eng. Progr. 60 (5), 49-54 (1964). (6D) Iron Age 190, 105 (April 30, 1964). (7D) Ibid.,191, 31 (June 3, 1965). (8D) .Machine U e s i p (March, 1965). (9D) M e c h . Eng. 87 ( 5 ) , 80 (1965). (10D) M o d . M e f n l r 19 (Z), 87 (1964). (11D) Zbid., 20 ( l ) , 36 (1965) (12D) Packaging 5 , 29 (1964). (13D) P e h / C h c m Engr. 37 ( i ) , 32 (1965). (14D) Welding Design Fhbrication 4, 41 (1965). (l5D) Welding Eng. 50 (3), 28 (1965), (16D) Wyma, B. H., Wagner, R. H., Chrm. Eng. Progr. 60 (5), 5 5 , 62 (1964).
