Properties of ATI 425® Alloy Tubing for Use in Aircraft Hydraulic Systems

New designs, and upgrades of legacy aircraft, are causing the aircraft OEM’s to incorporate 5,000+psi hydraulic systems into their latest models.  The use of the traditional alloy Ti 3Al-2.5V in these designs necessitates a heavier gauge wall than is required for 3,000 psi systems and can result in increased airframe weight.  Thus far, attempts to qualify higher strength tubing alloys such as Ti 6Al-4V Super ELI (SE) have been unsuccessful.  ATI 425^® Alloy (4Al-2.5V-1.5Fe-0.25O) is a cold workable titanium alloy demonstrating strength that is similar to Ti 6Al-4V and much higher than Ti 3Al-2.5V.  The cold workability of ATI 425^® Alloy allows the production of tubing without the concomitant reduction in oxygen required to make tubing out of Ti 6Al-4V.  Initial research showed that ATI 425^® Alloy exhibited improved fatigue properties over alloys such as Ti 6Al-4V SE and Ti 3Al-2.5V in sheet form.  In tubing form, these enhanced properties may support the use of ATI 425^® Alloy in a 5,000psi hydraulic system without an increased wall thickness and corresponding weight penalty.  This presentation focuses on the tensile, bend, flare, flatten, fatigue and burst properties of ATI 425^® Alloy tubing.  Properties are compared to Ti 3Al-2.5V.