The flux of magnesium alloy is mainly composed of MgCl2, KCl, CaF2, BaCl2 and other chlorine salt and fluorine salt. The use of alkali and alkali metals in the flux is due to their high chemical stability. Several kinds of salt are mixed in proportion to make the melting point, density, viscosity and surface property of the flux can meet the use requirements.
1. MgCl2 magnesium chloride
MgCl2 is the main component of magnesium alloy flux. It has good coverage and certain refining capacity for magnesium alloy melt. The melting point of MgCl2 is 981 K, which is easy to mix with other salts to form a low melting point salt mixture. MgCl2 also can well moisten the magnesium oxide on the melt surface and transfer it to the flux. This eliminates the adiabatic effect of magnesium oxide, which causes the heat of magnesium to be dissipated rapidly through the flux layer, and avoids a sharp rise in the temperature of the melt surface of the magnesium alloy. MgCl2 has a lot of hygroscopicity, and the exposed air is quickly exposed to moisture, and it reacts with oxygen and water vapor in the air to generate HCI, Cl2, H2, etc. The good refining of MgCl2 is that the liquid MgCl2 is good for MgO and Mg3N2 wettability, and it can effectively adsorb these inclusions in the melt. In addition, MgCl2 also has the role of chemical slag formation, and the resulting product MgCl2.5MgO can be precipitated from the melt. Thus, MgCl2 plays a major role in the refining process.
2. KCl potassium chloride
The melting point, surface tension, and viscosity of MgCl2 can be significantly reduced after the addition of KCI in MgCl2. Another function of KCl is to improve the stability of the flux, which reduces the evaporation loss of MgCl2 at high temperature and reduces the vapor pressure of MgCl2. The existence of KCl also greatly inhibits the hydrolysis process of MgCl2 heating and dehydration and reduces the loss of MgCl2 during the dehydration operation.
3. BaCl2 barium chloride
The density of BaCl2 is large, and the density of the liquid 1237K is 3.06g.cm3, and the density of the 293K solid is 3.87g.c m3. Barium chloride can be used as an aggravating agent of flux to increase the density difference between the flux and the melt of magnesium alloy, which can make it easier to separate the melt from the magnesium alloy melt. The addition of BaCI2 to the protective flux covering is not helpful. The melting point of barium chloride is 1233K and the viscosity is large, and the viscosity of the flux can be increased by adding to the flux.
4. NaCl sodium chloride
NaCl is the basic unit of flux, NaCl and MgCl2 and KCl constitute mgcl2-KCl-NaCl triples. Its presence increases the density of the flux and can be used to adjust the melting point.
5. CaF2 calcium fluoride
CaF2 can improve the viscosity and refining properties of the flux. CaF2 has a certain solubility in mgcl2-KCl-Naci triples, and when it exceeds this solubility, the undissolved Ca initial mass points appear in the liquid mixture salt, which greatly improves the viscosity of the mixed salt. CaF2+MgCl2=MgF2+CaCl generated MgF2 is very small in chlorine salt. And the solubility is not changing with temperature, MgF2 also has the ability to make slag from MgO. CaF2 improves the separation properties of slag and magnesium alloy liquid, and it has good slag mixing effect. It is convenient to remove the surface slag by adding the CaF2 to the melting agent.
6. MgF2, MgO fluoride, magnesium oxide
The solubility of MgF2 in chlorine salt is very small, and its existence changes the characteristics of the solubility of CaF2 with the change of temperature. Therefore, a small amount of CaF2 can thicken the flux, and the flux cannot be unstable due to temperature fluctuation. The existence of MgF2 can also improve the refining capacity of the flux because MgF2 has the ability to make up slag from MgO. It is also believed that after the addition of fluorine, the solubility of MgO in the flux is improved.
The flux has a close relationship with the spread, covering, refining capacity and the composition ratio of the melt. In the case of improper preservation of the qualified flux, the water content exceeding the standard will be added to the melt of magnesium alloy. The MgCl2 and water in the flux form MgO, and it forms a small group on the surface of the liquid, which can not spread and cover well, and it will lose the effect of refining. When there is a lot of water, the flux will spark in contact with the melt of magnesium alloy, and may even cause the spatter explosion of the melt of magnesium alloy.