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    The thermal conductivity of titanium rod and titanium alloy rod billet is low, which causes great temperature difference between the surface layer and the inner layer during hot extrusion. When the temperature of the extrusion barrel is 400 ° c, the temperature difference can reach 200~250 ° c.In inspiratory reinforcement and billet section under the common effect of large temperature difference, the center of the billet surface and the strength of the metal to produce vastly different performance and the plastic performance, can cause very uneven in the extrusion process, the deformation of the big gallas attached stress in the surface layer, forming a crack in the surface of extrusion products and the root cause of the crack.The hot extrusion process of titanium rod and titanium alloy rod is more complicated than that of aluminum alloy, copper alloy and even steel, which is determined by the special physical and chemical properties of titanium rod and titanium alloy rod.

    The flow kinetics of industrial titanium alloy metal shows that the flow behavior of metal varies greatly in the temperature zone corresponding to different phase states of each alloy.Therefore, one of the main factors affecting the extrusion flow characteristics of titanium rod and titanium alloy rod is the billet heating temperature which determines the metal phase transition state.The metal flow is more uniform when extruded in a or a+P phase than when extruded in P phase.It is difficult to obtain high surface quality of extruded products.Up to now, the extrusion process of titanium alloy rods has had to use lubricants.The main reason is that titanium at 980 ° c and 1030 ° c will form fusible eutectic crystals with iron – or nickel-based alloy mould materials, which will make the mould wear strongly.

Main factors affecting metal flow during extrusion:

1. Extrusion method.Reverse extrusion ratio forward extrusion metal flow evenly, cold extrusion ratio hot extrusion metal flow evenly, lubrication extrusion ratio non-lubrication extrusion metal flow evenly.The influence of extrusion method is realized by the change of friction condition

2. Extrusion speed.As the extrusion speed increases, the inhomogeneity of metal flow increases.

3. Extrusion temperature.When the extrusion temperature increases and the deformation resistance of billet decreases, the uneven flow of metal becomes more serious.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 metal in the center layer is large, the uneven flow of metal 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.In other conditions, 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 will be.

6. Degree of deformation.If the deformation is too large or too small, the metal flow is uneven.

Editor:Carrie Qi (rowlynti@rowlyn.com)