The thermal conductivity of titanium rod billets is low, which can cause a significant temperature difference between the surface and inner layers 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 suction strengthening and significant temperature difference in the cross-section of the billet, the metal on the surface and center of the billet produces extremely different strength and plastic properties. During the extrusion process, it will cause uneven deformation, generate large additional tensile stress in the surface layer, and become the root cause of cracks and fissures on the surface of the extruded product. The hot extrusion process of titanium rod products is more complex than that of aluminum alloys, copper alloys, and steel, which is determined by the special physical and chemical properties of titanium rods.

Research on the flow dynamics of industrial titanium alloy metals shows that there are significant differences in the flow behavior of metals in the temperature range corresponding to different states of each alloy. Therefore, one of the main factors affecting the extrusion flow characteristics of titanium rods is the heating temperature of the billet that determines the metal phase transition state. It is very difficult to obtain high surface quality for extruded products, and so far, lubricants must be used in the extrusion process of titanium alloy rods. The main reason is that titanium can form fusible eutectic with iron-based or nickel based alloy mold materials at temperatures of 980 ° C and 1030 ° C, resulting in strong wear of the mold.

The main factors affecting metal flow during extrusion:

1. Squeeze method. Reverse extrusion has a more uniform metal flow than forward extrusion, cold extrusion has a more uniform metal flow than hot extrusion, and lubricated extrusion has a more uniform metal flow than non lubricated extrusion. The influence of extrusion methods is achieved through changes in friction conditions.

2. Squeeze speed. The increase in extrusion speed exacerbates the non-uniformity of metal flow.

3. Squeeze temperature. As the extrusion temperature increases and the deformation resistance of the billet decreases, the uneven flow of metal intensifies. During the extrusion process, if the heating temperature of the extrusion cylinder and mold is too low, and the temperature difference between the outer layer and the center layer of the metal is large, the unevenness of metal flow increases. The better the thermal conductivity of the metal, the more uniform the temperature distribution on the end face of the ingot.

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

5. Mold angle. The larger the die angle (i.e. the angle between the end face of the mold and the central axis), the more uneven the metal flow. When using a porous die for extrusion, the arrangement of die holes is reasonable, and the metal flow tends to be uniform.

6. Deformation degree. The degree of deformation is too large or too small, and the metal flow is uneven.