What Are The Key Factors Affecting Metal Flow in Titanium Material Extrusion?

Extrusion molding is an important method for the plastic processing of titanium materials. The metal flow state is the core factors of the quality of extruded products; its uniformity directly affects the mechanical properties, dimensional accuracy, and surface quality of the products. Uneven flow can cause defects,like shrinkage cavities, cracks, and compositional segregation.

 

 

The crystal structure, chemical composition, and thermophysical properties of titanium materials are inherent factors. During extrusion, these factors determine the metal flow behavior and directly influence the plastic deformation capacity and flow resistance.

 

1. Crystal Structure and Phase Transformation Characteristics

• Phase transformation of pure titanium: At room temperature, it is α-Ti with poor low-temperature plasticity and uneven flow; above 882°C, it transforms into β-Ti with improved plasticity and more uniform flow.

 

• Influence of alloying elements: α-stabilizing elements such as Al and Sn increase the phase transformation temperature; β-stabilizing elements (Mo and V )decrease the phase transformation temperature. Precise temperature control according to composition is required to match the optimal flow

2. Chemical Composition and Impurity Content

• Influence of main components: Alter the high-temperature deformation resistance and plasticity; deviations in composition from the design range easily lead to uneven flow.

 

• Influence of impurities: O, N, and C increase resistance and reduce plasticity.it likely make cracking ; a small amount of Fe is beneficial to plasticity, but excessive Fe forms brittle phases that hinder flow. Need the strict impurity control.

3. Thermophysical Properties

• Low thermal conductivity: Deformation heat is difficult to dissipate, prone to local high temperatures, resulting in soft centers with fast flow and hard edges with slow flow, forming a flow velocity difference.

 

• Small linear expansion coefficient: Low volume contraction/expansion, but improper temperature control will generate thermal stress, shifting the flow direction and affecting dimensional accuracy.

 

 

1. Extrusion Temperature

The core is to adjust the material's phase structure by controlling the temperature range, balancing plasticity and performance.

• Low temperature (below the phase transformation point): Poor plasticity, easy cracking, and uneven metal flow, which should be avoided as much as possible.

 

• Medium temperature (close to the phase transformation point): α+β dual-phase region, requiring precise temperature control; otherwise, internal stress is likely to occur.

 

• High temperature (above the phase transformation point): Good plasticity and uniform flow, but excessively high temperature will cause grain growth and reduced strength.

 

• Example: Ti-6Al-4V alloy is commonly used at 920-980°C (α+β phase region) to balance plasticity and grain stability.

2. Extrusion Speed

Regulate the flow stability by controlling the deformation time and heat.

• Low speed: Uniform flow and good surface quality, but low production efficiency and easy mold adhesion.

 

• High speed: Rapid local temperature rise and accelerated flow, but prone to "advance flow", leading to dimensional deviation or cracks.

 

• Key point: Titanium materials have low thermal conductivity, so strict speed control is necessary. The common speed for pure titanium is 5-15mm/s, and for Ti-6Al-4V alloy is 3-10mm/s; exceeding 20mm/s is easy to defects.

3. Extrusion Ratio

Reflects the degree of material deformation, affecting flow uniformity and density.

• Small extrusion ratio (<10): Small deformation, flow concentrated in the center, and easy "subsurface porosity" at the edges.

 

• Large extrusion ratio (>10): Sufficient deformation, uniform flow, and high density, but large deformation resistance and easy mold wear.

 

• Example: 8-15 for thin-walled profiles and 15-25 for solid titanium rods, adapting to different product requirements.

4. Lubrication Conditions

Core function: Reduce friction between the mold and the material, facilitate uniform metal flow, and reduce mold wear and energy consumption.

• Key requirement: Titanium material extrusion temperature is high, and conventional lubricants are easy to failure; high-temperature resistant lubricants must be used.

 

• Preferred solution: Glass lubricants can form an isolation film, reducing the friction coefficient from 0.3-0.5 to 0.1-0.2, and also provide heat insulation and damage reduction.

 

• Risk warning: Insufficient lubrication or material failure will lead to "stagnant flow zones", causing product surface scratches and internal cracks.

 

Our Ruihang Group strictly select the raw materials to melt and refine the titanium ingots, supplying the high-quality titanium bars,plates and other titanium products after the plastic processing of titanium materials. For more details,please contact us via the Email: Sam.Rui@bjrh-titanium.com