Types of refractory materials for zirconium alloy precision casting

zirconiumAlloy precision castingIt means that the metal material is melted and then gravity-cast into the shell made of refractory and heat-insulating material. After the metal material is condensed, the mold is removed and the sand is removed to obtain the required alloy product. The use of alloy precision casting technology can forge complex castings, and they are close to the final shape of the part after forming. However, because the shell must touch the aluminum alloy melt immediately during forging, the selection of shell raw materials is important to ensure the quality of castings, such as zirconium and zirconium aluminum alloy with high melting point and strong organic chemistry specificity. . The melting point of zirconium and zirconium aluminum alloy is (1852±10) ℃, and the specificity of organic chemistry at high temperature is quite large. When melting, it will react with most refractory insulation materials, causing an environmental pollution layer on the surface of aluminum alloy. Therefore, it is important to obtain high-quality zirconium castings to select refractory insulation materials that do not react with zirconium melts as the mold shells for precision castings. Can be used with zirconium and zirconium aluminumAlloy precision castingThe key refractory insulation materials include high-purity graphite, refractory metal materials, refractory chemicals, metal oxides, etc.

High-purity graphite and bright metal materials such as titanium and zirconium have weak reactions. As early as the 1950s, European and American countries have used high-purity graphite shells to produce zirconium castings. As everyone knows, the high-purity graphite shell also has some defects. For example, the air oxidation just begins at around 430°C, and the ability to absorb steam is strong. Gravity casting must be carried out after high temperature degassing in a vacuum furnace; On the one hand, high-purity graphite has high thermal conductivity, which is very easy to cause chilling, and it is easy to cause micro-cracks on the surface of castings. Liu Hongyu scientifically researched the page reflections of zirconium solution and high-purity graphite shells in precision castings, and concluded that because of the high porosity of high-purity graphite, faster water cooling, and poor tolerance, the surface layer of the zirconium-aluminum alloy specimens showed significant Cold barriers and cracks, the environmental pollution layer of zirconium and high-purity graphite shell is about 20μm thick. Xie Huasheng and others have also obtained similar scientific research results. In addition, the C element has extremely poor corrosion resistance to zirconium aluminum alloy, which also limits the application of graphite materials on the level of zirconium aluminum alloy precision castings.

2 Refractory metal materials

Mo, Ta, W, Nb and other refractory metal materials with higher melting points have good reliability to titanium and zirconium metal materials, and can be used to make the structural layer of precision castings. In the whole process of making the mold shell, a layer of tungsten or tungsten metal oxide structure layer is generally formed on the surface of the porcelain, thereby reducing the reflection of the molten metal material and the mold shell. At this stage, the shells made by this kind of processing technology are mainly used in precision castings of titanium and titanium metal. Basche uses tungsten chemicals to infiltrate the porcelain shell, and then burns it in an oxidizing atmosphere to restore the tungsten chemicals, and then coat the surface of the refractory insulation material with tungsten, thereby preventing titanium from interfering with the refractory insulation material at high temperatures. reflect. However, this type of tungsten structure layered shell also has some shortcomings. For example, the solvent dewaxing method must be used to make the shell, which will seriously harm the natural environment and health; in addition, the mold material accumulated on the surface of the shell after dewaxing It is very easy to react with metal materials and transform into vent holes on the surface of the casting.