Sponge titanium is a lightweight, hard and honeycomb product. It can not be directly applied to the production of titanium products. It must be made by high temperature melting and dense titanium ingot to be applied to titanium processing. Titanium and titanium alloys are smelted with titanium sponge in a vacuum consumable arc furnace. The titanium particles and alloy materials are pressed into blocks, and the group is welded into a consumable electrode. The ingot smelting is carried out in a closed vacuum chamber. During the smelting process, it is impossible to adjust the chemical composition of the melt, so sponge titanium plays a very important role in the quality control of the ingot. Magnesium chloride will inevitably remain in sponge titanium produced by magnesium thermal reduction. These magnesium chloride will have adverse effects on electrodes, ingot and smelting equipment. Therefore, it is of great significance to improve the quality of the product in the production practice to study the influence of magnesium chloride residue on the melting and casting of titanium and titanium alloy.
The wetting of residual magnesium chloride leads to the appearance of precipitates on the surface of the electrode. The main residue of the titanium sponge produced by the magnesium heat process is magnesium chloride, which is easily dissolved in the air to produce hydrates. The hydrate is white, and the moisture content is proportional to the contact time of air humidity and contact. During the heating process, the water vapor and Magnesium Oxide decomposed by hydrous magnesium chloride will increase the oxygen content of the ingot. It has been shown that the bright rich alpha layer is easy to appear because of oxygen segregation. During the rolling process, the deformation of the two sides of the rich alpha layer is not harmonization, which leads to the increase of local stress and the brittle material, which causes the cracking.
The residual magnesium chloride has a great influence on the surface of ingot. The sediment on the surface of the ingot is composed of fine oxides, chlorides and other inclusions. The anhydrous magnesium chloride, covering the surface of the oxide, cooled and dissolved in the air and collected a large amount of water. When the deposition of magnesium chloride is more, it is placed for a period of time and there will be a solution of magnesium chloride. The residual heat of the ingot will make the solution dissolved by magnesium chloride evaporate part of the moisture, but it can not completely remove the moisture, so the sediment is sticky and attached to the surface of the ingot, so it is not easy to remove. A surface of the ingot has this "black" or "black spots" directly into the furnace, two times of melting, is bound to a large amount of water and oxide inclusions, which increases the difficulty to control the vacuum melting and casting, easy to produce quality defects such as porosity and inclusions.