Characteristics Of Hot Extrusion Process Of Titanium And Titanium Alloy Material

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 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.

(3) Metal strength. When other conditions are equal, the higher the metal strength, the more uniform the metal flow.

(4) Die 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.

(5) Degree of deformation. If the degree of deformation is too large or too small, the metal flow will be uneven.

(6) Extrusion speed. As the extrusion speed increases, the inhomogeneity of the metal flow increases.

The study of metal flow dynamics of industrial titanium alloys shows that the flow behavior of metals is greatly different in the temperature region corresponding to the different phase states of each alloy. Therefore, one of the main factors affecting the extrusion flow characteristics of titanium and titanium alloys 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 alloys 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 of the mold. When graphite lubricant is used, deep longitudinal scratch lines can be formed on the surface of the product, which is the consequence of titanium and titanium alloys sticking to the mold. When extruding profiles with glass lubricants, a new type of defect "pickles" can result, i.e. cracks in the surface layer of the product. Studies have shown that the appearance of "pockmarks" is due to the low thermal conductivity of titanium and titanium alloys, which causes the surface layer of the billet to cool violently and the plasticity to decrease sharply.