What Is Hot Extrusion Forming For Titanium Alloy Bars?

Hot extrusion serves as the core process for large‑scale and high‑precision preparation of titanium alloy bars. It can refine grains, homogenize microstructures, eliminate casting defects, and improve the mechanical properties and forming accuracy of bars. This paper introduces its technical principles and process characteristics, and analyzes the influence laws of key parameters including temperature, extrusion speed, deformation amount, die structure and lubrication system.

1.Technical Principle

Titanium alloy ingots are preheated to the plastic range and axially extruded to obtain dense bars. High‑temperature dynamic recrystallization breaks dendrites, closes pores, and optimizes metal flow lines as well as mechanical properties.

2.Process Characteristics

Compared with steel and aluminum alloys, titanium alloy hot extrusion features high temperature sensitivity, high high‑temperature activity and a narrow plastic window. The billet exhibits poor thermal conductivity, resulting in a large temperature difference between its interior and exterior. Reactions tend to occur between the material and dies at 980‑1030 °C, damaging both dies and workpieces. Deformation is only suitable in the α+β two‑phase region. Out‑of‑control temperature may lead to high deformation resistance, coarse grains or over‑burning defects.

• Heating Temperature

For Grade 5 alloy, extrusion in the two‑phase region at 850‑950 °C is preferred. Too low a temperature causes cracking, while excessive temperature leads to grain coarsening and over‑burning. Uniform temperature holding of billets is required.

• Extrusion Speed: (No content available)
• Extrusion Deformation Amount: The suitable extrusion ratio ranges from 6 to 15. A high ratio ensures sufficient deformation; an excessively low ratio leaves residual defects, whereas an excessively high ratio brings high load and large residual stress. Large‑size bars are mostly formed by multi‑pass extrusion, while small‑size bars can be produced by single‑pass extrusion.
• Die Structural Parameters: Optimize the die cone angle to 90° and set a reasonable bearing length. Adopt asymmetric multi‑hole dies to balance material flow velocity. Dies shall be made of high‑temperature‑resistant and anti‑sticking alloys.
• Lubrication and Protection System: Glass‑based lubrication is mainly adopted to form an isolating layer for anti‑sticking and anti‑oxidation. Uneven coating may induce surface defects.

1.Uneven temperature and significant anisotropy

Due to the poor thermal conductivity of titanium alloy, large cross‑sectional temperature difference exists in billets, giving rise to non‑uniform radial microstructures and poor consistency of mechanical properties, which fails to meet the requirements of high‑end equipment.

2.High‑temperature die sticking and frequent surface defects

Titanium shows high chemical activity at high temperature. Once lubrication fails, scratching and peeling occur on workpieces. Dies suffer heavy wear, resulting in low finished‑product rate and high production cost.

2.Complex parameter coupling and difficult process debugging

Parameters such as temperature and deformation amount interact with one another. Mismatched parameters easily cause various defects. The traditional trial‑and‑error method is low‑efficiency and low‑precision.

3.Insufficient forming stability for large‑size bars

Large‑size billets suffer uneven material flow and heat dissipation. Obvious property differences exist between the head, tail, inner and outer regions of bars, accompanied by high residual stress, which leads to cracking and deformation in subsequent processing.

1.Precise temperature control

Apply segmented gradient heating and heat preservation; preheat dies to 350‑450 °C. Select extrusion temperatures within the two‑phase region according to alloy grades to suppress defects caused by temperature difference.

2.Lubrication upgrading

Adopt composite glass lubrication and optimize coating procedures. Implement billet pretreatment and regular die maintenance to mitigate die sticking and surface defects.

3.Collaborative parameter regulation

Replace trial‑and‑error tests with finite element simulation to analyze multi‑parameter coupling rules and iteratively optimize processes for better product consistency.

3.Die optimization

Set the die cone angle to 90° and configure proper bearing length; polish and harden die cavities. Apply multi‑pass extrusion for large‑size bars to homogenize microstructures and release residual stress.

4.Collaborative heat treatment

Perform annealing, solution treatment and aging after extrusion to eliminate residual stress, reduce anisotropy and improve comprehensive mechanical properties.

Ruihang, as a direct manufacturer of titanium products, supply optimal quality raw materials for your precision components production. If you have any purchasing needs about titanium alloy bars/plates, please feel free to contact us via email: Sam.Rui@bjrh-titanium.com