Al Metal and Its Alloys

In a series of pubhcations, the results of anodic dissolution and passivation of well-defined single-crystal surfaces of Ni (and other metals) and its alloys were presented by Marcus et al. [19-24]. Their approach aimed at a better understanding... 

Structural Properties at Low Temperatures It is most convenient to classify metals by their lattice symmetiy for low temperature mechanical properties considerations. The face-centered-cubic (fee) metals and their alloys are most often used in the construc tion of cryogenic equipment. Al, Cu Ni, their alloys, and the austenitic stainless steels of the 18-8 type are fee and do not exhibit an impact duc tile-to-brittle transition at low temperatures. As a general nile, the mechanical properties of these metals with the exception of 2024-T4 aluminum, improve as the temperature is reduced. Since annealing of these metals and alloys can affect both the ultimate and yield strengths, care must be exercised under these conditions. 

As brass was a critical material during WWII, in Europe, the Germans started to use steel an d many cases were manufd from this material(Ref 28a,p Ger 27). As steel proved to be a satisfactory material, steel cases are now made in other countries including US(Refs 8,9,10,11,13, 15,17,21,24a 28). Other metals such as Al and its alloys(Refs 2,3,4 7) or Zn-Cu alloys(Ref 6) have also been tried. The possibility of using sintered iron Cartridges has been investigated at Frankford Arsn, Philadelphia(Ref 20), but further work is required. Plastic cartridge cases are described in Refs 12 27... 

Fig. 12.59. Depth profile of the concentration of OH for Al and Al alloys (a) Al, (b) Al-Mo, (c) Al-W, (d) Al-Ta. (Reprinted from J. O M. Bockris and J. Kang, The Protectivity of Aluminum and its Alloys with Transition Metals, J. Solid State Electrochem. 1 24,1997, with permission from Springer-Ver-lag.)...

Among the material properties of great importance and concern is design and choice of the material and its inherent resistance to corrosion. Significant and extensive experimental data on the corrosion rates of readily available metals and their alloys can be found in the literature.35,36 The relative corrosion resistance of some steels, nickel, brass, nickel-copper alloys and Al-Cu alloys in chosen atmosphere35 is shown in Table 1.13. 

While the use of pure metals and eutectic alloys as brazes is generally good practice, exceptions do occur. Thus it may be necessary to use brazes that deviate from eutectic compositions to minimise the concentration of an embrittling temperature depressant, or to complicate the melting characteristics and accept degraded fluidity by introducing elements that enhance the corrosion resistance of the solidified braze. Thus recommended Al-Si brazes have hypo-eutectic compositions and Cr is introduced into Ni-P and Ni-Si-B braze alloys. 

Thus the reaction of sodium chloride with titanium from the alloy, or rutile from the scale leads to the formation of TiCl2, Na2Ti03, HC1 and Cl2.This list of reactions is by no means exhaustive, and may also involve reaction with other alloying additions which may be substituted for the titanium metal. Particularly, the role of aluminium must be of importance. A thermodynamic analysis by Travkin et al. [32] confirms that complex oxide scales are formed when titanium and its alloys react with NaCl. Particularly that the formation of volatile metallic chlorides are thermodynamically favourable, especially for alloying additions Zr, Mo and Al. The subsequent pyrohydrolysis of these metal chlorides results in the formation of HC1 gas, particularly with Mod., and AlClj. Furthermore, such pyrohydrolysis of halide salts may be accelerated by the presence of alumina within the scales, which acts as a catalyst [25]. 

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