Research On Forming Process Of TA15 Alloy Under Bottom Pouring Vacuum Casting

TA15 alloy is a kind ofα-titanium alloy developed by the former Soviet Union. The alloy has low density and moderate room temperature and high temperature strength, good thermal stability and welding performance, which is widely used in the manufacture of various types of aircraft structural parts. Present titanium casting technology has investment casting, centrifugal casting, low pressure casting, etc., However, these techniques have problems.In this paper, a new type of casting forming process was used to achieve TA15 alloy castings forming. The filling capacity of TA15 alloy was studied under bottom pouring vacuum casting, revealing the effect of suction casting process conditions on the melt filling the mold, lay the foundation for realizing the application of the bottom pouring vacuum casting for titanium. In this paper, the influence of the current, suction hole diameter, mold temperature on the filling capacity of TA15 alloy is studied the solidification process and structure of TA15 alloy under the bottom pouring vacuum casting is analyzed.The results show that: Respectively using suction hole diameter of 3mm, 4mm graphite suction hole, the larger the diameter of graphite suction hole, the TA15 alloy filling capability the stronger; Current intensity are 250A, 300A, 350A, the results show that the stronger current, the greater arc in the smelting process, the higher temperature, TA15 alloy filling capability is good.Mold temperature are 40℃, 60℃, 100℃, the results show that the higher mold temperature, forms smaller melt and mold temperature difference ,TA15 alloy filling capability is stronger . Finally TA15 alloy 70mm×20mm×1mm thin sheets casting and impeller are successfully suction casted. Reasonable conditions of casting the thin sheet is: graphite suction hole diameter is 4mm, the current intensity is 500A, mold temperature is 140℃; Reasonable conditions of casting the complex impeller is: graphite suction hole diameter is 4mm, the current intensity is 400A, mold temperature is 100℃. Under the bottom pouring vacuum casting process conditions, the alloy liquid has a strong filling capacity not only in the direction of gravity but also the horizontal direction. The solidification process and the filling process of the impeller casting was simulated by ProCAST software, showing that TA15 alloy under the condition has a strong capacity to fill the thin wall, complex castings.In the bottom pouring vacuum casting method, Mold materials and mold structure are important factors affecting casting forming. The thickness of casting is important factor on grain size: the thinner castings, the faster castings cooling during the formation, the smaller the grains. As the mold thermal conductivity, density, specific heat etc are so different so as to melt solidification conditions are different in the same casting, leading castings grain size difference. The grains of castings in metal mold are smaller, which is the biggest in h-BN mold. However, the structures in different mold are all basketweave microstructure under the technology. Cooling conditions of different mold are different, surface hardness of the casting is different, in which the 1mm thickness plate castings in graphite mold has the largest hardness.