The thermal conductivity of titanium rods and titanium alloy rod blanks 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 combined influence of suction strengthening and significant temperature differences in the cross-section of the billet, the metal on the surface and center of the billet exhibits extremely different strength and plasticity properties. This results in uneven deformation during the extrusion process, leading to significant additional tensile stress in the surface layer and becoming the root cause of cracks and fissures on the surface of the extruded product. The hot extrusion process of titanium rods and titanium alloy rod products is more complex 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.

Research on the flow dynamics of industrial titanium alloys shows that there are significant differences in the flow behavior of metals in temperature zones corresponding to different phase states of each alloy. Therefore, one of the main factors affecting the extrusion flow characteristics of titanium rods and titanium alloy rods is the heating temperature of the billet that determines the metal phase transition state. Compared with temperature extrusion in the p-phase region, metal flow is more uniform in the a or a+P phase region. It is very difficult to obtain high surface quality for extruded products. So far, lubricants have been required for the extrusion process of titanium alloy rods. The main reason is that titanium forms eutectic with iron-based or nickel based alloy mold materials at temperatures of 980 degrees and 1030 degrees, causing strong wear on the mold.

The main factors affecting metal flow during extrusion are:

1) Squeezing method. Reverse extrusion results in uniform metal flow compared to forward extrusion, cold extrusion results in uniform metal flow compared to hot extrusion, and lubricated extrusion results in uniform metal flow compared to non lubricated extrusion. The influence of extrusion method is achieved through changes in friction conditions.

2) Squeezing speed. As the extrusion speed increases, the unevenness of metal flow intensifies.

3) Squeezing temperature. When 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 tube and mold is too low and the temperature difference between the outer and central layers of metal is large, the unevenness 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 ingot.

4) Metal strength. All other conditions being equal, the higher the strength of the metal, the more uniform the metal flow.

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

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