Summarize the Characteristics of Titanium and Titanium Alloy Casting

The metal molds used for the casting of titanium and titanium alloys are usually made of gray cast iron (HT150 or HT200), cast steel (ZG200-400), cast copper (pure copper or brass), and a very small amount of refractory metals (such as molybdenum). Except for refractory metals, the melting points of these materials are lower than those of titanium. They can be used as casting molds for casting titanium alloys for the following reasons:
(1) The thermal conductivity of these materials is higher than that of titanium, and the heat generated after the titanium liquid is poured into the mold is quickly transferred away;
(2) The thermal conductivity of titanium is low. After the titanium liquid touches the casting mold and contacts the mold surface, it immediately solidifies to form a thin shell, which can effectively increase the temperature gradient of the holding mold.
The above-mentioned metal casting materials have their own advantages and disadvantages:
(1) Cast iron has good rigidity, easy processing, low price, long life, and is stable to molten titanium at lower temperatures. At the same time, because it contains flaky graphite inside, titanium liquid has better wettability to it, which is beneficial to the filling of titanium liquid and the forming of castings. The disadvantages are its high linear expansion coefficient and low melting point. Therefore, it is usually only suitable for making the outer mold of castings, not suitable for core.
(2) Cast steel is similar to cast iron. It has higher strength and more durability than cast iron, but its deformation is slightly larger than cast iron.
(3) The thermal conductivity of cast copper is very high, but the strength is low and the rigidity is poor. It can only be used to make small castings. The price is high and it is rarely used.
(4) The refractory metal is resistant to high temperature, high hardness and wear resistance, but it is very brittle, expensive, and has poor workability. Mo is mainly used as a die-casting punch.
The key to metal mold casting lies in the design of the mold, which is directly related to the quality and dimensional accuracy of the casting, the life of the mold, the processing and manufacturing costs of the mold. In addition to the design principles of ordinary metal molds, the characteristics of titanium and titanium alloy casting must be considered. The following points can be summarized:
(1) The bottom bet should be used as much as possible;
(2) An open pouring system should be adopted;
(3) Try to use centrifugal casting, and design the structure and fixing method of the metal mold according to the requirements of centrifugal casting.
In order to reduce the cost of the metal type and increase the service life of the metal type, the metal type can be used in combination with the machined graphite type. All parts of the cavity that are not easy to mold and easy to damage can be embedded with graphite blocks, and all casting systems can use machined graphite. The casting model of titanium alloy artificial joint is a combination of metal type and machined graphite. The machined graphite parts must be baked at a higher temperature (not greater than 400°C) before pouring, preferably in a vacuum at 950-1000°C for 1.0-2.0h to remove the adsorbed gas.

Tags :
Categories :