What are the most innovative uses of Aluminum
1-LVDCPN > 12-17-2018, 07:22 AM
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抯 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抯 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 搊ther� 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抯 major competitors.
While Alcoa抯 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 搒calped� substantially to remove undesirable surface segregation.
William T. Ennor, of Alcoa抯 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抯 patent3 provided the basis for modern DC-casting technology, which was introduced into virtually all of Alcoa抯 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抯 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梩oday抯 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抯 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抯 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.
HEAT-TREATABLE ALLOYS
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梞ore than 726 tonnes in one year.8 Alcoa obtained the rights to Wilm抯 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.