The role of rare earth in aluminum and its alloy

Rare earth elements is very lively, extremely easily with gas (e.g. hydrogen), non-metallic (such as sulfur) and generate the corresponding stable compound metal effect. The atomic radius of rare earth calcium silicons is less than common metal, such as lead, magnesium, etc., in the solid solubility of these metals is extremely low, almost can't form a solid solution. In the rare earth elements added to the aluminum alloy can have the effect of micro alloying; In addition, it with gas such as hydrogen and many non-metallic strong affinity, can generate high melting point compounds, so it has certain than hydrogen, refining, purification effect; At the same time, the rare earth elements strong chemical activity, it can be selectively on has formed the grain interface adsorption, hinder the growth of the grain, with the result that grain refinement and qualitative change.
metamorphism
Modification Brown Corundums is to point to add a small amount of in metal and alloy or trace of inoculant, to change the alloy crystallization conditions, make its organization and performance improvement process. Metamorphic agent is also called the grain refining agent and nucleating agent. Typically, rare earth atomic radius. Because of rare earth elements is lively, it melt to fill easily in the liquid aluminum alloy phase surface defects, and reduces the surface tension of the old and the new two phase interface, make the crystal nucleus growth rate increased. At the same time it also can between grain and alloy liquid in the formation of surface active membrane, prevent generating of grain growth, thus refine the organization of the alloy. In addition, as an exotic crystal nucleus, aluminum and rare earth compounds in metal crystal formation, due to the large increase in number of crystal nucleus and thus refine the organization of the alloy. Rare earths in al-si alloy is mainly the metamorphism, make needle, lamellar eutectic silicon spherulitic, make less of the scale of the primary silicon. The stale ability is different, different rare earth La and Eu has strong metamorphism, and the mixture of rare earth and Ce only moderate ability of metamorphism. Lanthanide metamorphic ability has a close relationship with atomic radius, as the atomic radius from La to Er of 0.187 nm 0.175 nm, the metamorphic capacity decreases. All in atomic radius is less than 0.18 nm, metamorphism is reduced to the point of no practical significance. Different metamorphic ability of rare earth elements available critical cooling rate of deterioration (Vc), Vc is smaller, the bad effects, the more obvious; When V is smaller than that of Vc, any concentration of rare earth elements can cause alloy, this is one of the main difference between rare earth and other metamorphic agent.