In the melting of various alloys, melting Mg-Al-Zn alloy process is simple, Zirconium and smelting Mg-Zr alloy is more difficult, how to add zirconium is the main problem of the production of zirconium-containing magnesium alloy. Such as high-strength Mg-Zn-Zr system, Zirconium heat-resistant Mg-RE-Zr and Mg-Th-Zr series, high-strength heat-resistant Mg-Ag-Nd-Zr system and excellent comprehensive performance of Mg-Y-Zr New magnesium alloy. Zirconium Magnesium alloy with zirconium is difficult for the following reasons:
1, the melting point of zirconium is high (2123K), the density is large (6.5g / Cm3), Zirconium the melting point of magnesium is 924K, the density is 1.74g / Cm3, Zirconium so the zirconium in the magnesium liquid is difficult to dissolve in solid state, Poor, easy to precipitate or form segregation.
2, the solubility of zirconium in the magnesium alloy melt is small, 0.6% in the magnesium liquid, and less than 1% in the magnesium zirconium alloy solution, Zirconium which makes it difficult to add zirconium to the magnesium liquid to form the alloy, and it is difficult to make the composition uniform Mg-Zr master alloy.
3, zirconium chemical is very strong, high temperature easily with the atmosphere or magnesium liquid gas reaction, the formation of insoluble compounds (ZrO, ZrN, ZrH) to increase the zirconium loss.
4, there are many impurity metal elements hinder the addition of zirconium, such as magnesium, Al, Fe, Si, Ni, Mn and so on and zirconium does not melt and the material, Zirconium and precipitated in the bottom of the crucible, reducing the alloy melt zirconium content.
As a result of the above reasons, magnesium alloy containing zirconium smelting process is very strict. There are many ways to add, add mixed zirconium salt, intermediate alloy, Zirconium potassium fluorozirconate and so on. Potassium fluoride, potassium sulfate, mixed zirconium salt treatment temperature is high, the absorption rate is low, too much reaction residue, adding alloy is ideal, Zirconium low melting point of intermediate alloy, easy to use, less inclusions, alloying effect is good. Add the temperature and mode when adding the intermediate alloy。