Aluminium-manganese alloys

In a famous paper by Shechtman et al. (1984) electron diffraction patterns were shown of rapidly quenched and solidified aluminium-manganese alloys. Sharp diffraction peaks, suggesting long-range translational order, were observed with the presence however of five-fold symmetry (that is of a non-crystallographic symmetry see 3.6.1.1). By different orientation of the specimen five-fold axes (in 6 directions), three-fold axes (in 10 directions) and two-fold axes (in 15 directions) were identified with the subsequent observation of the existence also of an inver-sion centre the assignment of this phase to the icosahedral point group, m36, was defined. 

The Arsenazo III method has been utilized for determining Sc in minerals [51]. Scandium in mixtures with rare earth elements was determined by derivative spectrophotometry with the use of Chlorophosphonazo-p-Cl [27]. p-Acetyl-chlorophosphonazo with Ce(III) has been used for determining Sc in copper, aluminium, manganese, and magnesium alloys [28]. Traces of scandium in silicate rocks and sediments were determined with the use of Bromopyrogallol Red [43]. 

Because of choking of the nozzle due to the disturbance of the flux cover on the molten metal, this material is not normally used in hot metal machines. Alloys are available with a very low manganese content which minimises the formation of the aluminium-manganese precipitation which causes the sludge to form. This material is, however, used satisfactorily with the cold-chamber machines, where it is poured at about 680 C. 

Aluminium-Manganese. The Al-rich part of this system includes the intermetallic phases AUMn (above 710 C) and AleMn (Fig. 3.1-17). The a-Al solid solution and the Al6Mn phase form a eutectic (Fig. 3.1-17). The solubility of Mn in Al at room tenperature is negligibly small. In hypereutectic Al—Mn alloys, pre-... 

The metal looks like iron it exists in four allotropic modifications, stable over various temperature ranges. Although not easily attacked by air. it is slowly attacked by water and dissolves readily in dilute acids to give manganese(II) salts. The stable form of the metal at ordinary temperatures is hard and brittle—hence man ganese is only of value in alloys, for example in steels (ferroalloys) and with aluminium, copper and nickel. 

The effects on oxidation resistance of copper as a result of adding varying amounts of one or more of aluminium, beryllium, chromium, manganese, silicon, zirconium are described in a number of papers Other authors have investigated the oxidation of copper-zincand copper-nickel alloys , the oxidation of copper and copper-gold alloys in carbon dioxide at 1 000°C and the internal oxidation of various alloys ". ... 

Dilute binary alloys of nickel with elements such as aluminium, beryllium and manganese which form more stable sulphides than does nickel, are more resistant to attack by sulphur than nickel itself. Pfeiffer measured the rate of attack in sulphur vapour (13 Pa) at 620°C. Values around 0- 15gm s were reported for Ni and Ni-0-5Fe, compared with about 0-07-0-1 gm s for dilute alloys with 0-05% Be, 0-5% Al or 1-5% Mn. In such alloys a parabolic rate law is obeyed the rate-determining factor is most probably the diffusion of nickel ions, which is impeded by the formation of very thin surface layers of the more stable sulphides of the solute elements. Iron additions have little effect on the resistance to attack of nickel as both metals have similar affinities for sulphur. Alloying with other elements, of which silver is an example, produced decreased resistance to sulphur attack. In the case of dilute chromium additions Mrowec reported that at low levels (<2%) rates of attack were increased, whereas at a level of 4% a reduction in the parabolic rate constant was observed. The increased rates were attributed to Wagner doping effects, while the reduction was believed to result from the... 

It is widely recognised that improved resistance to sulphur attack can be obtained in commercial alloys by small additions of certain elements, notably manganese, silicon and aluminium. Figure 7.43 shows how the depth of metal converted to scale, and more particularly the total penetration by sulphur, is reduced by increasing silicon content in nickel-chromium-iron... 

Remarkably little has been published on corrosion fatigue crack propagation in copper and its alloys. In general little or no influence of marine environments has been observed in crack propagation experiments on manganese and nickel-aluminium bronzes although the frequencies employed were quite high (> 2.5 Hz) ... 

Both silicon and aluminium are added to zinc to control the adverse effects of iron. The former forms a ferro-silicon dross (which may be removed during casting). Aluminium forms an intermetallic compound which is less active as a cathode than FeZn,] . Similarly in aluminium and magnesium alloys, manganese is added to control the iron . Thus in aluminium alloys for example, the cathodic activity of, FeAl, is avoided by transformation of FeAlj to (Fe, Mn)Al/. This material is believed to have a corrosion potential close to that of the matrix and is, therefore, unable to produce significant cathodic activity . 

We have seen that the adverse effect of impurities can, within limits, be controlled by alloying additions. Thus silicon and aluminium are added to zinc, and manganese to aluminium and magnesium, to counter the effect of iron. 

The discussion so far has been limited to the structure of pure metals, and to the defects which exist in crysteds comprised of atoms of one element only. In fact, of course, pure metals are comparatively rare and all commercial materials contain impurities and, in many cases also, deliberate alloying additions. In the production of commercially pure metals and of alloys, impurities are inevitably introduced into the metal, e.g. manganese, silicon and phosphorus in mild steel, and iron and silicon in aluminium alloys. However, most commercial materials are not even nominally pure metals but are alloys in which deliberate additions of one or more elements have been made, usually to improve some property of the metal examples are the addition of carbon or nickel and chromium to iron to give, respectively, carbon and stainless steels and the addition of copper to aluminium to give a high-strength age-hardenable alloy. 

Duralumin (alloy of aluminium, magnesium, copper and manganese) used for structural purposes, e.g. in aircraft construction. 

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