Six Factors Affecting Metal Flow During Extrusion Of Titanium Alloy Materials
The thermal conductivity of titanium rod and titanium alloy rod billet is low, which will cause a huge 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 200~250 degrees. Under the joint influence of air suction strengthening and the large temperature difference in the billet section, the metal on the surface and center of the billet produces very different strength properties and plastic properties, which will cause very uneven deformation during the extrusion process. A large additional tensile stress is generated in the middle, 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 that of aluminum alloys, copper alloys, and even steel, which is determined by the special physical and chemical properties of titanium rods and titanium alloy rods.
The research on metal flow dynamics of industrial titanium alloys shows that in the temperature region corresponding to the different phase states of each alloy, the flow behavior of metals is greatly different. Therefore, one of the main factors affecting the extrusion flow characteristics of titanium rods and titanium alloy rods is the billet heating temperature that determines the metal phase transition state. Metal flow is more uniform when extruded at the temperature of the a or a+P phase region than at the temperature of the p phase region. It is very difficult to obtain high surface quality for extruded products. Until now, the extrusion process of titanium alloy rods had to use lubricants. The main reason is that titanium will form a eutectic eutectic with iron-based or nickel-based alloy mold materials at temperatures of 980 degrees and 1030 degrees, which will cause severe wear and tear on the mold.
The main factors affecting the flow of metal during extrusion:
1) Extrusion method. Reverse extrusion has more uniform metal flow than forward extrusion, cold extrusion has more uniform metal flow than hot extrusion, and lubricated extrusion has more uniform metal flow than non-lubricated extrusion. The influence of the extrusion method is achieved by changing the friction conditions.
2) Extrusion speed. As the extrusion speed increases, the inhomogeneity of the metal flow increases.
3) Extrusion temperature. The uneven flow of metal intensifies when the extrusion temperature increases and the deformation resistance of the billet decreases. 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 non-uniformity of metal flow will increase. The better the thermal conductivity of the metal, the more uniform the temperature distribution on the end face of the billet.
4) Metal strength. When other conditions are equal, the higher the metal strength, the more uniform the metal flow.
5) Mold angle. The larger the mold angle (that is, the angle between the end face of the mold and the central axis), the more uneven the metal fluidity. When the multi-hole die is used for extrusion, the die holes are arranged reasonably, 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 flow will be uneven.
