6 major factors affecting metal flow during extrusion of titanium alloy materials

The thermal conductivity of titanium rod and titanium alloy rod blank is low, 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 200~250 degrees. Under the combined influence of inhalation strengthening and the large temperature difference of the billet section, the metal on the surface and the center of the billet has 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 extruded product, which becomes the source of cracks and cracks formed on the surface of the extruded product. The hot extrusion process of titanium rods and titanium alloy rods 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 metal flow dynamics study of industrial Titanium Alloy Threaded Rods shows that in the temperature region corresponding to the different phase states of each alloy, the flow behavior of the metal is very 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 billet that determines the state of metal transformation. The metal flow is more uniform when extruding at the temperature of the a or a+P phase compared to the extrusion at the temperature of the p phase. It is very difficult to obtain high surface quality of extruded products. Until now, the extrusion process of titanium alloy rods had to 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 strong wear of the mold.

The main factors affecting metal flow during extrusion:

1) Extrusion method. The reverse extrusion is more uniform than the forward extrusion, the cold extrusion is more uniform than the hot extrusion, and the lubricated extrusion is more uniform than the non-lubricated extrusion. The effect 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. When the extrusion temperature increases and the deformation resistance of the billet decreases, the uneven flow of the metal intensifies. 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 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) 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 is. When the porous 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 is uneven.