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The function of impurity elements in aluminum alloy(2)

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It is mainly used as modifier in cast aluminum alloy, and deformed aluminum alloy is rarely used. Bismuth is replaced only in Al Mg wrought aluminum alloy to prevent sodium embrittlement. Antimony is added to some Al Zn mg Cu alloys to improve the process properties of hot pressing and cold pressing.



In wrought aluminum alloy, the structure of oxide film can be improved and the burning loss and inclusion during melting and casting can be reduced. Beryllium is a toxic element, which can cause allergic poisoning. Therefore, aluminum alloys in contact with food and beverages cannot contain beryllium. Beryllium content in welding materials is usually controlled at 8 μ Below g / ml. The content of beryllium should also be controlled for aluminum alloys used as welding substrates.



It is almost insoluble in aluminum, the maximum solid solubility is less than 0.0025%, and the melting point of sodium is low (97.8 ). When sodium is present in the alloy, it is adsorbed on the dendrite surface or grain boundary during solidification. During thermal processing, the sodium on the grain boundary forms a liquid adsorption layer. When brittle cracking occurs, naalsi compound is formed. There is no free sodium and "sodium embrittlement" does not occur. When the content of free magnesium is 2%, the content of free magnesium is 2%. Therefore, sodium salt flux is not allowed for high magnesium aluminum alloy. The method to prevent "sodium brittleness" is chlorination method, so that sodium forms NaCl and is discharged into the slag, and bismuth is added to make it form na2bi and enter the metal matrix; Adding antimony to form na3sb or adding rare earth can also play the same role.





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