The forming process of titanium rod and titanium alloy rod under hot extrusion

Titanium rods and titanium alloy rod blanks have low thermal conductivity, which will cause a great temperature difference between the surface layer and the inner layer during hot extrusion. When the temperature of the extrusion cylinder is 400 degrees, the temperature difference can reach 200 to 250 degrees. Under the combined influence of suction strengthening and the large temperature difference of the blank section, the metal on the surface and the center of the blank produces very different strength and plastic properties, which will cause very uneven deformation during the extrusion process. Large additional tensile stress is generated in the extruded product, which becomes the source of cracks and cracks on the surface of the extruded product. The hot extrusion process of titanium rods and titanium alloy rod products is more complicated than the extrusion process of aluminum alloy, copper alloy, and even steel, which is determined by the special physical and chemical properties of titanium rods and titanium alloy rods.

Industrial titanium alloy metal flow kinetics research shows that in the temperature zone corresponding to the different phase states of each alloy, the metal flow behavior is greatly different. Therefore, one of the main factors affecting the extrusion flow characteristics of titanium rods and titanium alloy rods is the heating temperature of the blank that determines the state of the metal phase transformation. Extrusion at the temperature of a or a+P phase zone compares with extrusion at the temperature of p phase zone, the metal flow is more uniform. It is very difficult to obtain high surface quality for extruded products. So far, the extrusion process of titanium alloy rods must use lubricants. The main reason is that titanium will form a fusible eutectic with iron-based or nickel-based alloy mold materials at temperatures of 980 degrees and 1030 degrees, which will cause the mold to wear strongly.

 The main factors affecting metal flow during extrusion:

(1) Extrusion method. Reverse extrusion is more uniform than forward extrusion, cold extrusion is more uniform than hot extrusion, and lubricated extrusion is more uniform than non-lubricated extrusion. The influence of the extrusion method is realized by changing the friction conditions.

(2) Extrusion speed. As the extrusion speed increases, the unevenness of the metal flow increases.

(3) Extrusion temperature. When the extrusion temperature increases and the deformation resistance of the blank decreases, the uneven flow of the metal increases. During the extrusion process, if the heating temperature of the extrusion cylinder and the mold is too low, and the metal temperature difference between the outer layer and the center layer is large, the unevenness of the metal flow will increase. The better the thermal conductivity of the metal, the more uniform the temperature distribution on the end surface of the ingot.

(4) Metal strength. When other conditions are the same, the higher the metal strength, the more uniform the metal flow.

(5) Die angle. The larger the die angle "(that is, the angle between the end face of the die and the central axis), the more uneven the metal fluidity. When using porous die extrusion, the die hole arrangement is reasonable, and the metal flow tends to be uniform.

(6) Degree of deformation. If the degree of deformation is too large or too small, the metal will flow unevenly.

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Types and production technology of titanium pipes for marine engineering

Titanium alloy pipes are divided into seamless pipes and welded pipes.

Titanium alloy seamless pipes are generally processed by extrusion + rolling or diagonal rolling piercing + rolling. Hot extrusion is a plastic processing technology that uses the principle of plastic material deformation to use a die to make a titanium alloy blank into a material with a certain shape, thickness and performance in a hot state. It is a complex process that combines plastic deformation and flow deformation. The material is in a state of three-way compressive stress during extrusion, which is beneficial to the plasticity of the material. The economic pressing process mainly uses rice to produce seamless pipes, bars and profiles for drinking gold. The main processing parameters of the extrusion process include extrusion ratio, extrusion temperature, extrusion speed and so on. When extruding the tube, a hollow tube made of titanium alloy loose material through deep hole processing or hot pressure perforation is also used as the original blank. The size of the hollow tube blank is determined by the inner diameter of the extrusion barrel of the extruder. Due to the high viscosity of drink alloys, copper, mild steel or other metals are usually covered during extrusion, or the surface of titanium alloy is covered with grease, glass lubricant, etc. for extrusion. Through extrusion, titanium alloy thick-walled pipes or titanium alloy pipes that do not require high dimensional accuracy can be directly prepared. High-precision alloy seamless pipes are generally produced by rolling technology. The billets are generally extruded pipe blanks. Commonly used pipe rolling methods include two-half pass cold rolling, two-roll ring pass cold rolling, and multi-roll cold rolling. Rolling, two-target warm rolling and multi-roll warm rolling, etc. For pure titanium with low strength and high plasticity, it is generally produced by cold rolling. The deformation of the pass is generally controlled at 20% to 60%. Annealing treatment is required between passes to eliminate work hardening and restore plasticity. For medium and high-strength titanium alloys, due to high tensile strength, large deformation resistance and poor processing plasticity: the warm-drying technology must be used when rolling seamless pipes, that is, induction heating devices or flame heaters are installed on the rolling mill. The heating temperature is controlled at about 100°C below the recrystallization temperature.

For large-diameter thick-walled titanium composite pipes: generally, the skew-rolling piercing method is also used for production. The cross-rolling piercing method uses tensile stress along the weave and transverse directions of the rolled blanks to cause micro-cracks in the core area of ​​the circular material, and then expand into a loose area. The use of high-temperature-resistant plugs enables the plastic deformation of the metal in the loose area: direct forming of the tube from the city. The heating temperature of the billet in this method is higher, which is beneficial to improve the new cracking properties of the pipe to achieve the purpose of high production efficiency, high material utilization rate and low production cost. Titanium alloy welded pipes are generally produced by welding, and welded pipes are produced with high precision A very efficient method for thin titanium alloy pipes: its production process is: titanium strip coil slitting → forming → welding → shaping and sizing ~ heat treatment straightening eddy current/ultrasonic inspection → airtight inspection of finished welded pipes. The production process is generally continuous production: The product quality has high stability, and the pipes produced are generally used for heat exchangers, condensers, etc.

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Development of pure titanium sheet with excellent surface manufacturability for building materials

In the beach area, titanium has excellent corrosion resistance, low thermal expansion, and lightweight, suitable for use as the roof and outer wall materials of buildings, so pure titanium thin plates are used in buildings around the world. Why use titanium as the roof and outer wall? This is because titanium not only has excellent corrosion resistance but also its design, environmental harmony, and other landscapes are also very important, that is, to pursue craftsmanship: ① various surface finishing according to needs; ② atmospheric environment

Improved technology for resistance to discoloration in ③; ③Development of a technique for suppressing depression caused by rolling;

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