ALUMINUM 24 FEBRUARY 2014 Q&A BY TONY ANDERSON Q: I understand that aluminum is a relatively new material when compared with steel. What is the history of aluminum and aluminum welding? A: To appreciate the history of aluminum welding, it is helpful to understand the history of aluminum itself. About the Metal As widely used and important as aluminum is in our lives today, you would suspect that it has been around for a very long time. In actuality, the process of converting aluminum ore (bauxite) into the metal that we know and use today as aluminum was discovered relatively recently. One of the earliest known pieces of ironware was excavated from an archaeological site in Anatolia and thought to be about 4000 years old. Ancient steel found in East Africa dates back to 1400 BC. In the 4th century BC, steel weapons like the falcata (a sickle-shaped sword) were produced in the Iberian Peninsula (modernday Spain, Portugal, Andorra, part of France, and Gibraltar). Around the same time in ancient history, Noric steel, from Noricum (modern-day Austria and part of Slovenia, and during that time part of the Roman Empire) was used by the Roman military. In contrast, the industrial production of aluminum only began in the late 19th century, making this material very much a latecomer among the common metals. For many years, people had tried without success to develop something comparable to what we now know as metallic aluminum. The primary reason for such a late development of this metal was the difficulty of economically extracting it from its ore. The ore combines strongly with oxygen in a compound that, unlike iron, cannot be reduced in a reaction with carbon. In 1886, two men (see Fig. 1) working in different countries simultaneously discovered the electrolytic process for producing aluminum that is still used today. Charles Martin Hall and Paul L. T. Heroult developed a workable electrolytic process (the Hall-Heroult process) that formed molten aluminum when purified alumina was dissolved in a molten salt called cryolite and electrolyzed with direct current. By 1914, the Hall-Heroult process had brought the cost of aluminum down amazingly. Aluminum was now becoming an accessible material that could be used for many applications. Subsequently, the production of aluminum multiplied dramatically. Fig. 1 — In 1886, these two men working in different countries, Hall in the U.S.A. and Heroult in France, simultaneously discovered the electrolytic process for producing aluminum that is still used today. Their discovery was the initial long-awaited step that made aluminum, once a precious metal used for fine jewelry, into an accessible material for many applications. In 1918, it had already reached the 180,000 ton level, and it has maintained steady long-term growth ever since. The production and consumption of aluminum grew, on average, through the mid- 1970s more than 8% per year. The total consumption of aluminum in the western world reached 2 million tons in 1952 and 20 million tons in 1989. Aluminum had been recognized as a material of the future. Welding Aluminum After the initial discovery of a suitable method to produce aluminum as a costeffective material, the next step was to modify and improve upon the basic material. Pure aluminum has some unique and very important characteristics, its corrosion resistance and electrical conductivity being two. However, pure aluminum, because of its relatively low strength, was not the most suitable material for structural applications. It was soon found that by adding relatively small amounts of alloying elements to pure aluminum, major changes could be made to the material’s properties. One of the first aluminum alloys to be produced was the aluminum-copper alloy. Around 1910, the phenomenon of precipitation hardening in this family of alloys was discovered. Many of these precipitation hardened alloys would produce immediate interest within the developing aircraft industry. Base Alloys 2024, 2219, and 7075, all precipitation-hardened alloys used in the aircraft and aerospace industries, were registered with the aluminum association in 1954. Along with the highstrength, heat-treatable aluminum-copper and aluminum-zinc alloys, many other alloys were developed; one of these was the nonheat-treatable 3xxx series manganese alloys, which were predominantly used for cookware. The 3xxx series alloys were found to have excellent properties at elevated temperatures, and for that reason, are still used today for manufacturing heat exchangers. It was found that by adding such elements as copper (Cu), manganese (Mn), silicon (Si), magnesium (Mg), and zinc (Zn) along with combinations of these elements, various physical and mechanical characteristics of pure aluminum could be dramatically changed. Many of these new alloys could match the strength of good quality carbon steel at one-third the weight. The development of many new aluminum alloys, which were suitable for structural application, immediately posed the question of suitable joining methods.
Welding Journal | February 2014
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