Vacuum die casting technology for aluminum and titanium alloy profiles

Aluminum titanium alloy profile that is in the industrial pure titanium alloy elements added to improve the strength of titanium, titanium alloy thermal conductivity is low, only steel 1/4, aluminum 1/13, copper 1/25. titanium alloy can be divided into three kinds of titanium alloys: a titanium alloy, b titanium alloy and a + b titanium alloy. ab titanium alloy is made of a and b biphasic composition, this kind of alloy organization is stable, high temperature deformation properties, toughness, plasticity is better, and can be quenched, Ageing treatment, so that the alloy is strengthened. The performance characteristics of titanium alloys are mainly manifested in:
1. High specific strength. Aluminum and titanium alloy profile density is small (4.4kg/dm3) light weight, but its specific strength is greater than ultra-high strength steel.
2. High thermal strength. Aluminum and titanium alloy profiles are thermally stable, and their strength is about 10 times higher than that of aluminum alloy under the condition of 300-500℃.
3. High chemical activity. Titanium can have a strong chemical reaction with oxygen, nitrogen, carbon monoxide, water vapor and other substances in the air, forming TiC and TiN hardened layer on the surface.
4. Poor thermal conductivity. Poor thermal conductivity of titanium alloy, titanium alloy TC4 at 200 ℃ thermal conductivity l = 16.8W/m - ℃, the thermal conductivity is 0.036 card/cm - sec - ℃.
As the application of titanium castings in the aerospace industry continues to grow, are committed to seeking production methods that can reduce production costs to replace high-cost titanium parts, especially in today's competitive world economy. As a result, lower-cost titanium castings with mechanical properties similar to those of forgings can replace not only existing titanium components, but also components made of other materials.VDC technology has been developed for the production of high-quality, low-cost titanium castings. Typical applications for its castings include aircraft fuselages (e.g. bulkheads, brakes, gears, hinges, etc.) as well as other aerospace and industrial components.
Vacuum die casting and investment casting of Ti-6Al-4V alloy cast rod of the organization and mechanical properties of the comparative study shows that the two kinds of cast rods in 899 ℃, 103MPa pressure, 2h hot isostatic pressure treatment, and then in 834 ℃, 2h vacuum annealing, vacuum die casting rods, the grain size of about 100 μm, the grains of any direction of the α-β structure The grain size of the melt mold casting bar is 750μm; the yield strength of the vacuum die casting material (930.79MPa) is about 12% higher than that of the melt mold casting material (827.37MPa), which is close to the yield strength of the forgings and rolled - annealed parts (896.32MPa); the fracture toughness of the vacuum die casting Kq is 142.8 MPa; close to the melt mold castings, but higher than the value of 87.9 MPa/m for annealed forgings.

Die casting technology for the production of aluminum, magnesium, zinc, copper-based alloy castings, in the machinery manufacturing industry application has been many years of history. These die castings are produced by melting the metal in the atmosphere and then injecting the molten metal into the casting mold under high pressure. Castings for net shape or near net shape, casting slightly after treatment or processing can get the final shape of the part, the process processing cycle is short, from the molten metal to the net shape of the part of the time is usually less than 15 s. On the titanium die casting technology requirements and the traditional alloy is completely different, the most important thing is the metal melting chamber and casting mold cavity must maintain a high vacuum, or else the casting of the oxygen content will be increased, can't satisfy the aviation alloys of the technical conditions. Vacuum die-casting titanium casting method and standard die-casting process, just melt room / mold cavity vacuum time and titanium alloy melting time to be extended. Vacuum die casting process using titanium alloy separate charge, induction shell melting. This is compared with the continuous casting method of die casting aluminum, its melting time to consume 5min more.
Compared with other methods such as investment casting method, vacuum die casting titanium castings process is simple, so the cost is generally lower. Vacuum die casting process does not need to remove wax, shell and chemical cleaning, process reduction of nearly half, compared to investment casting or forging process, can save about 30% of the cost. Because of the vacuum die casting mold directly with the molten titanium liquid contact, its service life has been shortened, compared with the investment casting method of its mold part of the cost is larger. At present, the vacuum die-casting method can only cast some whole, single-sided, simple shape of titanium castings, and mold casting can casting shape is very complex castings, hollow castings. In addition, vacuum die casting each time the maximum casting only 12 pieces, casting the maximum size of 61cmx46cmx25cm, the maximum mass of 18kg.