Precipitation strengthening

Almost every commercial precipitation strengthened aluminum ahoy contains magnesium as an ahoying element. The Al—Mg system (Fig. 13) has a eutectic at 35% magnesium [7439-95-4] Mg, and 451°C. Maximum soHd solubiHty is 14.9% Mg, and solubiHty decreases to about 0.8% Mg at room temperature. Despite this decreased solubiHty, precipitation strengthening by the mestable P -phase precursor to the equhibrium P phase Al3Mg,... 

In addition to these principal alloying elements, which provide soHd solution strengthening and/or precipitation strengthening, wrought alloys may contain small amounts of titanium and boron [7440-42-8J, B, for control of ingot grain size, and ancillary additions of chromium, manganese, and zirconium to provide dispersoids. AH commercial alloys also contain iron and siUcon. 

S is solution strengthened D, dispersed phase P, precipitation strengthened SA, special addition. 

Hydrogen has to be safely stored and transported. Therefore, hydrogen resistant alloys for containers, such as FeNiCr stainless steel, FeNiCr strengthened with N and Mn, y -precipitated strengthening superalloy, have been developed at our institute. 

Two kinds of alloys resistant to hydrogen embrittlement can be used for hydrogen containers FeNiCr stainless steel and FeNiCr stainless steels strengthened with N. Mn and nanosize /-precipitates strengthened superallovs. 

Solution and Precipitation Strengthening by F. R. N. Nabarro, in The Physics of Metals Vol. 2. Defects edited by P. B. Hirsch, Cambridge University Press, London England, 1975. Nabarro s article provides an interesting perspective on the thinking concerned with the interactions of dislocations with obstacles. 

The active strengthening mechanism at room temperature of the studied material was identified as solid solution strengthening, grain boundary strengthening, and Al3Zr precipitate strengthening. 

Aluminum is a low melting point metal, therefore microstructural stability (and consequently creep) is an important issue even for near ambient temperature. Many common structural aluminum alloys are precipitation strengthened at heat treatment temperatures on the order of 423 K, implying that the service temperature must be considerably lower. There are a few aluminum alloys designed for high-temperature applications however, creep makes them unacceptable as materials of construction for contaimnent of pressurized gas at elevated temperature. On the other hand, aluminum alloys are commonly employed at cryogenic temperatures. 

MW Perra and RE Stoltz, Sustained-load cracking of a precipitation-strengthened austenitic steel in high-pressure hydrogen , in Hydrogen Effects in Metals, IM Bernstein and AW Thompson, Eds., The Metallurgical Society of AIME, New York, 1981, pp. 645-53. 

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