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  • 1. alloy of alluminium Al-Li From Wikipedia, the free encyclopedia Jump to: navigation, search Al-Li alloys are a series of alloys of aluminium and lithium, often also including copper and zirconium. Since lithium is the least dense elemental metal, these alloys are significantly less dense than aluminium. Commercial Al-Li alloys contain up to 2.45 wt% lithium.[1] Alloying with lithium reduces structural mass by two effects: • Displacement- a lithium atom is lighter than an aluminium atom; each lithium atom then displaces one aluminium atom from the crystal lattice, while maintaining the lattice structure. Every 1% by weight of lithium added to aluminium reduces the density of the resulting alloy by 3% and increases the stiffness by 5%.[1] This effect works up to the solubility limit of lithium in aluminium, which is 4.2%. • Στραιν ηαρδενινγ- The lithium atom is larger than an aluminium one. Introducing a larger atom into the crystal strains the lattice, which helps block dislocations. The resulting material is thus stronger, which allows less of it to be used. Al-Li alloys are primarily of interest to the aerospace industry, due to the weight advantage they provide. They are currently used in a few commercial jetliner airframes, and the AgustaWestland EH101 helicopter.[2]. As of 2006[update], the third, and current version of the U.S. Space Shuttle's external tank is principally made of Al-Li.[3] In addition, Al-Li alloys are also used on both the Atlas V and Delta IV EELV rockets, and before its cancellation were to be used by NASA for Project Constellation, primarily on its Ares I and Ares V rockets, as well as the Orion spacecraft. Some Al-Li alloys, such as Weldalite 049, are weldable; however, this property comes at the price of density; Weldalite 049 has about the same density as 2024 aluminium and 5% higher elastic modulus. Al-Li alloy swarf, scrap and other recycled material must be kept separate from other aluminium streams during recycling, as mixing Al-Li alloy with conventional aluminium recovery streams will cause extreme fire and explosion hazards.[4]
  • 2. Alnico From Wikipedia, the free encyclopedia Jump to: navigation, search Alnico is an acronym[1] referring to metal alloys which are composed primarily of aluminium (symbol Al), nickel (symbol Ni) and cobalt (symbol Co), hence al-ni-co, and iron, with the addition of copper, and sometimes titanium. Alnico alloys are ferromagnetic, and used to make permanent magnets. Before the development of rare earth magnets in the 1970s, they were the strongest type of magnet. Other trade names for alloys in this family are: Alni, Alcomax, Hycomax, Columax, and Ticonal.[2] The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe. The development of alnico began in 1931, when T. Mishima in Japan discovered that an alloy of iron, nickel, and aluminum had a coercivity (resistance to loss of magnetism) of 400 Oe, double that of the best magnet steels of the time.[3] Contents [hide] • 1 Properties • 2 Υσε • 3 Ρεφερενχεσ • 4 Φυρτηερ ρεαδινγ • 5 Εξτερναλ λινκσ [edit] Properties Alnico alloys make strong permanent magnets, and can be magnetized to produce strong magnetic fields. Of the more commonly available magnets, only rare-earth magnets such as neodymium and samarium-cobalt are stronger. Alnico magnets produce magnetic field strength at their poles as high as 1500 gauss (0.15 tesla), or about 3000 times the strength of Earth's magnetic field. Some brands of alnico are isotropic and can be efficiently magnetized in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic, with each having a preferred direction of magnetization, or orientation. Anisotropic alloys generally have greater magnetic capacity in a preferred orientation than isotropic types. Alnico's remanence (Br) may exceed 12,000 G (1.2 T), its coercivity (Hc) can be up to 1000 oersted (80 kA/m), its energy product ((BH)max) can be up to 5.5 MG·Oe (44 T·A/m). This means alnico can produce a strong magnetic flux in closed magnetic circuit, but has relatively small resistance against demagnetization.
  • 3. Alnico is produced by casting or sintering processes.[4] Anisotropic alnico magnets are oriented by heating above a critical temperature, and cooling in the presence of a magnetic field. Both isotropic and anisotropic alnico require proper heat treatment to develop optimum magnetic properties — without it alnico's coercivity is about 10 Oe, comparable to technical iron, which is a soft magnetic material. After the heat treatment alnico becomes a composite material, named "precipitation material"—it consists of iron and cobalt rich[5] precipitates in rich-NiAl matrix. Alnico's anisotropy is oriented along the desired magnetic axis by applying an external magnetic field to it during the precipitate particle nucleation, which occurs when cooling from 900 °C (1,650 °F) to 800 °C (1,470 °F), near the Curie point. Without an external field there are local anisotropies of different orientations, due to spontaneous magnetization. The precipitate structure is a "barrier" against magnetization changes, as it prefers few magnetization states requiring much energy to get the material into any intermediate state. Also, a weak magnetic field shifts the magnetization of the matrix phase only, and is reversible. Alnico alloys have some of the highest Curie points of any magnetic material, around 800 °C (1,470 °F), although the maximum working temperature is normally limited to around 538 °C (1,000 °F).[6] They are the only magnets that have useful magnetism even when heated red-hot.[7] This property, as well as its brittleness and high melting point, is the result of the strong tendency toward order due to intermetallic bonding between aluminium and its other constituents. They are also one of the most stable magnets if they are handled properly. As of 2008, Alnico magnets cost about $44/kg ($20/pound) or $4.30/BHmax.[8] [edit] Use Alnico magnets are widely used in industrial and consumer applications where strong permanent magnets are needed; examples are electric motors, electric guitar pickups, microphones, sensors, loudspeakers, traveling wave tubes, and cow magnets. In many applications they are being superseded by rare earth magnets, whose stronger fields (Br) and larger energy products (BHmax) allow smaller size magnets to be used for a given application. Duralumin From Wikipedia, the free encyclopedia Jump to: navigation, search Its first use was rigid airship frames. Its composition and heat treatment were a wartime secret. With this new rip-resistant mixture, duralumin quickly spread throughout the aircraft industry in the early 1930s, where it was well suited to the new monocoque
  • 4. construction techniques that were being introduced at the same time. Duralumin also is popular for use in precision tools such as levels because of its light weight and strength. Although the addition of copper improves strength, it also makes these alloys susceptible to corrosion. For sheet products, corrosion resistance can be greatly enhanced by metallurgical bonding of a high-purity aluminium surface layer. These sheets are referred to as alclad, and are commonly used by the aircraft industry.[3]

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