1. Why Extrude Titanium Bars
Hot extrusion produces titanium bars by forcing a heated billet through a die, which shapes the metal in a single operation with high material utilisation. The process suits round, square, hexagonal and rectangular sections and can achieve lengths that are difficult to obtain by forging alone. The deformation refines the cast structure of the ingot and produces a fibrous grain flow that improves the mechanical properties in the longitudinal direction.
2. Billet Preparation
The starting billet is cut from a forged or rolled intermediate, and its surface is conditioned to remove oxide scale, cracks and other defects. The billet is then machined to the required dimensions and inspected before heating. Surface quality matters because defects on the billet are drawn out along the bar during extrusion and can leave longitudinal surface flaws. Clean billets give clean bars.
3. Heating and Lubrication
The billet is heated in a controlled furnace to a temperature that depends on the grade, typically in the range of 850 to 1050 °C for commercially pure and alpha-beta titanium alloys. Overheating above the beta transus is avoided for alpha-beta alloys because it coarsens the microstructure. Glass-based lubricants are applied to the billet and die to reduce friction, prevent galling and protect the metal surface from oxidation during the flow through the die.
4. Extrusion Parameters
The extrusion press applies force to push the billet through the die at a controlled ram speed. The reduction ratio, which is the ratio of the billet area to the product area, is selected to give full recrystallisation and a uniform structure. The temperature at the die exit is monitored because it controls the microstructure and the surface quality. Excessive speed raises the temperature through deformation heat and can cause surface cracking, while very slow speeds allow the billet to cool and increase press load.
5. Cooling and Post-Processing
After extrusion the bar is cooled at a controlled rate, and the cooling rate determines the final microstructure. Air cooling is typical for commercially pure grades, while alloy bars may require furnace cooling or faster cooling depending on the target properties. The bar is then straightened, annealed if required, and finished by peeling or turning to remove the surface layer. Finally the bar is cut to length, inspected and tested.
6. Quality and Applications
Extruded titanium bars are tested to ASTM B348 or GB/T 2965, including chemical analysis, tensile testing and ultrasonic examination. They are used for machined components, fasteners, fittings, shafts and structural parts in aerospace, chemical and marine industries. The certification documents the composition, mechanical properties and heat treatment of each lot, giving the purchaser full traceability.
Billet temperatures of 850 to 1050 °C are typical for titanium extrusion.
Glass lubricants protect the surface and reduce die friction.
Bars are finished by peeling, straightened and certified to ASTM B348.
Frequently Asked Questions
Q: What shapes can be extruded in titanium?
Round, square, hexagonal and rectangular solid bars are common, and more complex profiles can be extruded with shaped dies.
Q: What temperature is used for titanium extrusion?
Typical billet temperatures are 850 to 1050 °C depending on the grade, and the temperature is kept below the beta transus for alpha-beta alloys.
Q: Why is glass lubrication used?
Glass lubricants reduce friction and galling at high temperature and protect the titanium surface from oxidation during extrusion.
Q: How is the bar surface finished after extrusion?
The bar is usually peeled or turned to remove the oxidized surface layer, then straightened and annealed as required.
Q: What tests are done on extruded bars?
Chemical analysis, tensile testing, hardness, ultrasonic examination and dimensional checks, reported on the mill certificate.
