Vanadium forms VAl11 refractory compound in aluminum alloy, which plays a role in refining grains in the melting and casting process, but the effect is smaller than that of titanium and zirconium. Vanadium also has the effect of refining the recrystallization structure and increasing the recrystallization temperature.
The solid solubility of calcium in aluminum alloy is extremely low, and it forms CaAl4 compound with aluminum. Calcium is also a superplastic element of aluminum alloy. Aluminum alloy with about 5% calcium and 5% manganese has superplasticity. Calcium and silicon form CaSi, which is insoluble in aluminum. Since the amount of solid solution of silicon is reduced, the conductivity of industrial pure aluminum can be slightly improved. Calcium can improve the cutting performance of aluminum alloy. CaSi2 cannot strengthen the heat treatment of aluminum alloy. Trace calcium is beneficial to remove hydrogen in molten aluminum.
Lead, tin, and bismuth elements are low-melting metals. They have little solid solubility in aluminum, which slightly reduces the strength of the alloy, but can improve the cutting performance. Bismuth expands during solidification, which is beneficial for feeding. Adding bismuth to high magnesium alloys can prevent “sodium brittleness”.
Antimony is mainly used as a modifier in cast aluminum alloys, and is rarely used in wrought aluminum alloys. Only substitute bismuth in Al-Mg wrought aluminum alloys to prevent sodium embrittlement. When the antimony element is added to some Al-Zn-Mg-Cu alloys, the performance of hot pressing and cold pressing can be improved.
Beryllium can improve the structure of oxide film in wrought aluminum alloy and reduce burning loss and inclusions during casting. Beryllium is a toxic element that can cause allergic poisoning. Therefore, aluminum alloys that come into contact with food and beverages cannot contain beryllium. The content of beryllium in welding materials is usually controlled below 8μg/ml. The aluminum alloy used as the welding base should also control the content of beryllium.
Sodium is almost insoluble in aluminum, the maximum solid solubility is less than 0.0025%, and the melting point of sodium is low (97.8°C). When sodium exists in the alloy, it is adsorbed on the surface of dendrites or grain boundaries during solidification. During thermal processing, sodium on the grain boundary forms a liquid adsorption layer, and when brittle cracking occurs, NaAlSi compound is formed, no free sodium exists, and “sodium brittleness” does not occur. When the magnesium content exceeds 2%, magnesium will take silicon and precipitate free sodium, resulting in “sodium embrittlement”. Therefore, high-magnesium aluminum alloys are not allowed to use sodium salt fluxes. The method to prevent “sodium embrittlement” is the chlorination method, which makes sodium form NaCl and discharges it into the slag, and adds bismuth 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.
Edited by May Jiang from MAT Aluminum
Post time: Nov-11-2023
