In high-end manufacturing fields such as aerospace and medical devices, titanium bars and titanium alloy bars occupy an irreplaceable position due to their excellent physical and chemical properties. However, compared to common metals like aluminum and copper alloys, the extrusion process of titanium materials is more complex, with uneven metal flow being the core issue that causes cracks and surface defects in products. Today, let's take a deep dive into the key factors affecting metal flow during titanium extrusion and see how to make titanium materials 'flow obediently'!
Characteristics of titanium materials: inherently 'troublesome.' Titanium bars and titanium alloy billets have extremely low thermal conductivity, meaning that during hot extrusion, there is a significant temperature difference between the surface and the interior of the billet-when the extrusion cylinder reaches 400°C, the temperature difference can be as high as 200–250°C. This temperature difference, combined with titanium's tendency to absorb gas, leads to significant differences in strength and plasticity between the surface and the center, directly causing uneven deformation during extrusion. The surface experiences additional tensile stress, ultimately resulting in surface cracks and fissures.
More importantly, the heating temperature of the billet determines the phase state of the titanium alloy, and metals behave very differently in different phase zones. During extrusion in the α or α+β phase regions, metal flow is relatively uniform, but even so, achieving high surface quality remains challenging. In contrast, extrusion at β phase temperatures further exacerbates uneven flow. Additionally, titanium at temperatures above 980°C can form low-melting eutectics with iron-based and nickel-based alloy dies, leading to severe die wear. This means that titanium alloy extrusion must rely on lubricants; otherwise, it cannot proceed smoothly.
Extrusion process: the 'key lever' for external control. Extrusion method: choosing the right method avoids detours; backward extrusion is more uniform than forward extrusion. Extrusion speed: slow work yields fine results; controlling the extrusion speed and giving the metal sufficient deformation time is crucial for uniform flow. Extrusion temperature: higher is not always better; temperature control requires technical skill.
Metal properties and dies: details determine success or failure. Beyond the material itself and process parameters, factors like the metal's inherent strength and die design quietly influence the uniformity of metal flow. Metal strength: a 'hard bone' can actually be more obedient. Die angle design: if the angle is wrong, efforts are wasted. Deformation degree: too much or too little is detrimental; just the right amount is best. Therefore, precise control of deformation is a vital prerequisite for ensuring uniform titanium material flow.
