From a monument to the Vega: the journey of the aluminum casting industry.
Compared with other cast metals, aluminum has had a short, but at times colorful and controversial history. From the discovery of pure aluminum in 1825 until the present represents a period of just under 175 years. While this is a long time when projected against today's rapid rate of technology change, aluminum is still the "new kid on the block" in the foundry industry.
The oldest known castings are copper utensils, such as hammers and knives, which were first produced 10,000-11,000 years ago. There is evidence that copper was melted and cast into shapes as early as 3700 B.C. The oldest casting in existence is a copper frog believed to have been cast in 3200 B.C. in Mesopotamia. Copper and tin were first combined to produce bronze about 3000 years ago.
Items of cast iron have been discovered in Egypt dating to a 500-year period from 1100 to 600 B.C. Cast iron was so common in China in the 12th century that it was used for the roofs of pagodas.
This early history of copper and cast iron, however, is unusual in light of the fact that aluminum is the most abundant metal on earth and the third most abundant element on earth - exceeded only by oxygen (O) and silicon (Si). The earth's crust is 8% aluminum and the commercial bauxite that we use to produce the metal is 40-60% aluminum. Bauxite is available in unlimited supply, and when commercially usable bauxite is depleted there are inexhaustible deposits of aluminum silicates that are 20-30% aluminum. Despite aluminum's slow start out of the gate, it has grown in little more than a century and a half from virtually a chemical curiosity to the world's second most commonly used metal.
Early Cast Aluminum
Historians credit Denmark's Hans Oerstad for chemically isolating aluminum from aluminum chloride in 1825 using a potassium amalgam. Later, Germany's Friederich Wohler used metallic potassium for isolation, and France's Henri DeVille used metallic sodium instead of potassium.
The Oerstad and Wohler processes produced only small quantities of aluminum that were expensive, inconsistent and not of high purity. Several attempts to electrolytically isolate aluminum were tried during that period without much success. The electric battery had been in existence only a few years and the aluminum produced using batteries was in limited quantities and expensive. The
price of aluminum as recorded in literature is unreasonably high, but aluminum was considered a precious metal at that time, not because of a scarcity of raw materials but because of the difficulty of separation of the metal.
Aluminum was so difficult to produce electrolytically because the electric dynamo was not invented until 1870. Before that time, all the electricity had to come from batteries, and it was difficult to produce sufficiently high energy rates to accomplish efficient aluminum reduction.
The first authenticated aluminum castings were produced by Colonel William Frishmuth at his foundry in Philadelphia in 1876. The castings were small parts used to make an engineer's transit. At that time Frishmuth's foundry was "the entire aluminum casting industry." These first castings were made from $1/oz chemically produced aluminum.
A summation of the industry's difficulties is described in Scientific American in 1879 by a knowledgeable and deeply involved practitioner, Clemens Winchler, who wrote, "There are several reasons why the metal is shown so little favor. First of all, there is the price. Then the methods of working it are not everywhere known - and further, no one knows how to cast it."
The Washington Monument
Frishmuth's crowning achievement was pouring the most famous aluminum casting ever produced - the cap for the Washington Monument in our nation's capital. The Washington Monument was conceived in 1783 after the end of the Revolutionary War but was not completed until 1884. The final design was a 555-ft obelisk of white marble. The design called for an aluminum-bronze [90% (copper) Cu-10% aluminum] cap plated with gold or platinum to be connected to copper rods running all the way to the ground (so the cap would serve as a lightning rod). Aluminum-bronze was readily available and was produced using an electric resistance furnace.
Frishmuth convinced designers that it could be made of aluminum and finished with nothing more than a simple polishing. The casting weighed more than 6 lb with walls 0.5-in. thick. The pyramid was 9-in. tall and almost 6 in. on a side at the base. The metal composition was 1.7% iron (Fe), 0.55% Si and the balance aluminum, and a cast iron mold was used for the pour. The price of the aluminum material was $1/oz. Subsequent examinations have shown no evidence of hydrogen porosity or oxide inclusions.
The Hall Process
In 1886, Charles Martin Hall, 22, a student at Oberlin College, Oberlin, Ohio, discovered the process of producing pure aluminum by passing an electric current through a mixture of aluminum oxide (alumina) dissolved in molten cryolite in a carbon-lined furnace with a carbon anode. Cryolite is a double fluoride of aluminum and sodium. At almost the exact same time, Paul Heroult developed the same process in France. As a result, an extended period of highly contested litigation took place as both men tried to receive the patent rights for the process. Because the court in this country tended to favor the American, Hall was finally granted the patent and thus the name Hall prevails.
At the same time that Hall was defending his patent rights against Heroult, he was involved in a bitter dispute with the Cowles brothers (as reported in The True Story of Aluminum by Alfred Cowles, Jr., son of one of the Cowles brothers) who were in the furnace business (Cowles Electric Smelting and Aluminum Co.) and had been producing aluminum bronze using an internally heated electrolytic furnace. The Cowles brothers contended that without their furnace, Hall could not have successfully produced aluminum because his furnace design was not workable.
Hall's argument was that the Cowles brothers could not produce aluminum in their furnace without Hall's formula for alumina mixed properly in cryolite. After years of litigation between Hall and his backers (Pittsburgh Reduction Co.) and the Cowles brothers, Hall prevailed in the courts and his firm went on to commercially produce aluminum. It was Judge William Howard Taft who decided in favor of Hall - the same Taft who later became U.S. president.
The aluminum industry blossomed with the development of the Hall process and the price of aluminum dropped from $15/lb in 1884 to $0.50/lb by 1890. By the turn of the century, the use of aluminum castings was growing rapidly. Ten years after Hall developed his process, the American Foundrymen's Assn. was founded by 345 delegates meeting in Philadelphia on May 12, 1896.
The First Autos and Kitty Hawk
The development of the automobile at the turn of the century created opportunities for aluminum castings. While aluminum engines are thought to be only the result of gasoline shortages, some of the first automobiles had cast aluminum engine components.
If the cap on the Washington Monument is the most famous aluminum casting, the block and crankcase of the Wright Brothers' first plane to fly at Kitty Hawk in 1903 are the second most famous. The castings were sand cast from an alloy of 8% Cu and 92% aluminum (later known as #12 alloy) and weighed 152 lb. The cylinder liners were cast iron, as were the pistons, valve heads and flywheel. The crankcase walls were 0.13-0.16-in. thick. Most of the plane's frame was wood as the first all-aluminum plane did not appear until 1921.
With the birth of the auto industry and the aircraft industry, aluminum casting technology began to expand rapidly. In the early 1900s the first patent was issued for low-pressure permanent mold and in 1905 the diecasting machine was patented by H.H. Doehler (one of the founders of Doehler-Jarvis). In 1907, the hot chamber diecasting machine was introduced.
One of the most significant developments in the history of the aluminum casting industry was the discovery in 1907 by Alfred Wilm that certain aluminum alloys respond to thermal treatment. Wilm was performing developmental work on aluminum alloys that contained 4% Cu and 0.5% magnesium (Mg). He was heating test specimens to 940F (504C) and then quenching them in water. By accident, he allowed some quenched test specimens to sit over the weekend before checking the mechanical properties. When he checked the specimens on Monday, he learned that by allowing time for room temperature aging the mechanical properties improved. The experiments that followed were the beginning of solution heat treating and artificial aging to enhance aluminum alloy properties.
At the same time as Wilm's discovery of heat treating, Hall's Pittsburgh Reduction Co. became the Aluminum Co. of America (Alcoa). Most of the early development work in the industry was done by Alcoa. Because it had a virtual monopoly in aluminum production, it had the financial resources to do extensive research and development. World War I generated a great demand for high-integrity castings for aircraft engines and Alcoa developed the #122 alloy, a 10% Cu, 1.25% Fe and 0.25% Mg alloy.
Aluminum Casting Develops
In the 1920s, the permanent mold process was making great advances. During the period between World War I and World War II, aluminum-Si alloy pistons were switched from sand to permanent mold (which is still standard for internal combustion engines).
The year 1921 saw another significant development in the industry - the modification of the Si structure in aluminum-Si alloys. A man by the name of Pacz is credited with the process of adding metallic sodium to the molten aluminum just prior to pouring to produce greatly improved ductility. The aluminum-Si alloys had been popular with foundrymen because of their castability but had always been outperformed by the aluminum-Cu alloys in terms of ductility. Although modifying the Si structure created soundness problems, they were overshadowed by the improved mechanical properties. In today's industry, strontium and antimony have joined metallic sodium as common modifiers, with antimony being used more extensively in Europe and Japan.
In 1925, X-ray radiography became a tool for checking casting quality, and by 1936 the Navy required that many of the castings it bought be X-rayed prior to acceptance. By 1940, all military aircraft castings required X-ray inspection prior to acceptance.
In 1928, Alcoa developed the first aluminum vehicle wheel. It had spokes and duplicated a wooden wheel. It was sand cast in 355 alloy and was designed for truck trailers. This application for wheels came years after aluminum had been used for engine components. Before 1930, most aluminum castings were part of the internal combustion engine - pistons, crankcases, oil pans, gear covers and cylinder heads. Most of these castings were aluminum-Cu alloys, with a Cu content up to 14%.
The aluminum-Cu alloys had good mechanical properties but poor corrosion resistance. The aluminum-Si alloys were more castable and, thus, represented an ever-increasing share of the market. Despite aluminum's popularity in the automobile engine, it fell far behind cast iron in tonnage produced because of the decided cost advantage of iron over aluminum. It was not until weight became a factor that aluminum played a leading roll in passenger-car design.
World War II
During and just prior to World War Il was a period of dramatic change in the aluminum casting industry. Prior to the war, Alcoa had a virtual monopoly in the aluminum industry. However, due to the demand for aluminum in all forms during the war, the U.S. government built new reduction plants. By the end of the war, the government owned 70% of the aluminum reduction capacity in the country.
In 1941, Kaiser and Reynolds entered the industry. At the same time, the federal government filed an anti-trust lawsuit against Alcoa that lasted for 10 years. After many appeals, Alcoa lost the suit. As a result, there was more competition in the foundry ingot business, but Alcoa was less willing to invest resources on casting research.
At the end of World War II there was concern about the state of the industry with the dramatic drop in the need for castings by the military-aircraft producers. The industry's salvation was that the iron and steel foundries were swamped with orders for ferrous castings to satisfy a market starved for new autos, machinery, and all sorts of industrial and civilian goods. The aluminum foundries, with the advanced technology acquired during the war, now were able to compete with iron and steel foundries. As a result, the industry did not have to downsize as was originally feared.
Gating System Research
In 1947 shortly after the war, the Battelle Memorial Institute, Columbus, Ohio, started a research project under the supervision of the AFS Light Metals Div. It was a study of various gating systems using clear plastic molds and water. The purpose was to determine the relationship between the cross-section of the sprue, the runner and the ingates. After the tests were run in plastic molds, they were repeated using sand molds and aluminum. The actual castings were X-rayed to prove that the systems did work. The initial work was done on horizontal gating systems and then on vertical systems.
When the work was finished in 1955, the industry had the first comprehensive set of formulas for use in designing sand and permanent mold gating systems for aluminum casting. This study was valuable to the jobbing foundry where casting design and complexity are constantly changing. The principles developed by the AFS-Battelle Institute research have stood up for 44 years and are still being used today.
The latest breakthrough in this area is the work that John Campbell is performing at the Univ. of Birmingham, England. He is using real-time X-ray radiography to study new approaches to gating and to identify the effect of metal velocity and the introduction of thin oxide films to the solidifying casting. These thin, entrapped oxide films have been shown to reduce mechanical properties, particularly fatigue properties.
Growth of Aluminum Casting
The 1950s and '60s saw the greatest growth in the production of aluminum castings. Since most of the aluminum casting alloys in use today had been developed by 1950, foundries were focused on improving aluminum casting soundness and mechanical properties. From 1956-1966, production of aluminum castings increased 107% (while ferrous casting production only increased 13%). In 1957, aluminum overtook copper as the second choice in metals to cast. During this period, a majority of the growth for aluminum occurred in die, permanent mold and investment casting.
If the cap on the Washington Monument and the engine block of the Wright Brothers' first flight at Kitty Hawk are the two most significant aluminum castings ever produced, the engine block of the Chevrolet Vega represents the most significant series of aluminum castings ever produced. In 1969, General Motors introduced the Chevrolet Vega, which had an all-aluminum block with no cast-iron cylinder liners. The block was diecast using the Acurad process. The alloy was 390 (developed by Reynolds) with 16-18% Si, 4-4.5% Cu and the balance aluminum. The high Si content increased wear resistance by allowing primary crystals of Si to precipitate. Two-and-a-half million Vegas were produced during the car's life cycle. The Vega block was different from all the earlier cast blocks in that it had no liners. The success of the Vega block still is under review today and has led to further work on aluminum alloy engine blocks.
In the 1960s, the integral aluminum automobile wheel and drum were produced in permanent molds using a cast-iron liner and 356 alloy. Today, aluminum wheels are almost standard throughout the industry.
The future changes for aluminum will be related to the molding process. While most aluminum castings today are produced in sand and permanent molds (and variations) and as die castings, lost foam castings are beginning to make an impact (Saturn for example). A recent survey conducted by James Hunter at the Univ. of Wisconsin in Milwaukee found that in 1997 140,000 tons of aluminum were poured in lost foam and associated processes (such as full mold and ceramic shell) (see modern casting's September 1998 issue, p. 50). The study also indicated that 256,000 tons were expected to be poured in 2000. The survey suggests that in 9 years (2008) 29% of aluminum castings will be made in lost foam. The drive for this continues to be the automobile industry.
This has been the theme through history of the aluminum casting industry. Automobiles have been the single most important factor in the development of aluminum casting and remain that way today as they probably will in the future.
Jack R. Bodine retired in 1990 as executive vice president and co-owner of Bodine Aluminum, Inc., St. Louis, after 40 years with the company. An active participant in AFS, Bodine served as AFS president from 1979-80, Cast Metals Institute (CMI) trustee from 1967-71, chairman of CMI trustees from 1970-71 and director of CMI classes from 1979-81. Bodine was also active with other associations, serving as president of the Non-Ferrous Founders' Society (NFFS) and past national trustee of the Foundry Educational Foundation. He also served as president of the St. Louis chapters of AFS, NFFS and the American Assn. of Industrial Management. Bodine received his B.S. in industrial engineering and his MBA from Washington Univ. and a B.S. in metallurgical engineering from Univ. of Missouri-Rolla. He and his wife Mary Jane reside in St. Louis.
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|Author:||Bodine, Jack R.|
|Date:||May 1, 1999|
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