Grain size, magnesium alloys

Small amounts of yttrium (0.1 to 0.2%) can be used to reduce the grain size in chromium, molybdenum, zirconium, and titanium, and to increase strength of aluminum and magnesium alloys. 

Figure 20. Dependence of the dendritic parameter and nondendritic grain size on a cooling rate for aluminum (1-8, 11), magnesium (9, 12), and nickel (10, 13) alloys. (1-10) Spacing between axes of 2nd order. (11-13) Nondendritic grain size.

Yttrium-aluminum garnet, with a hardness of 8.5, is used as a gemstone (imitation diamond). In small amounts (0.1-0.2 %), yttrium can be added to chromium, molybdenum, zirconium and titanium to the reduce grain size of these metals. Magnesium and aluminum alloys possess increased strength when small amounts of yttrium are added. Also the metal is used as a deoxidizer for vanadium and other non-ferrous metals (Hammond 2015). 

Microstructural properties such as grain size and phase distribution also play a role in determining corrosion behavior (Albright, 1988). Recent studies (Aune, 1983 Lunder et al., 1987) have found that fine, uniformly dispersed, cathodic phases were the most detrimental to the corrosion resistance of magnesium-based alloys (Albright, 1988). 

Small alloy additions are made to zinc to improve grain size, give work hardening, and improve properties such as creep resistance and corrosion resistance. There are a number of proprietary compositions available containing additions of copper, manganese, magnesium, aluminum, chromium, and titanium. 

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