Grade 5 alloy is a medium-strength α-β type two-phase titanium alloy containing 6% α-stabilizing element Al and 4% β-stabilizing element V. This alloy possesses excellent comprehensive properties and is widely used in the aerospace industry. The alloy can operate at temperatures up to 400℃ for extended periods. In the aerospace industry, it is mainly used to manufacture engine fan and compressor discs and blades, as well as important load-bearing components such as beams, joints, and bulkheads in aircraft structures.
The main semi-finished products of Grade 5 titanium alloy are bars, forgings, thick plates, thin plates, profiles, and wires. The alloy is primarily used in the annealed state, but can also be strengthened to some extent through solution aging treatment; however, the hardened cross-section generally does not exceed 25mm. This alloy has good process plasticity and superplasticity, making it suitable for various pressure forming processes. The alloy can also be welded and machined using various methods.
Ingots should be melted in a vacuum consumable electrode arc furnace at least twice. Materials for engine rotor parts should be melted three times. The alloying element V is added as an Al-V master alloy. Tungsten inert gas (TIG) welding is strictly prohibited for consumable electrodes; argon-shielded plasma welding is required.
When annealing semi-finished products or parts, the holding time depends on the cross-sectional thickness. For cross-sectional thicknesses less than or equal to 10 mm, the holding time should not exceed 30 min; for 11-50 mm, it should be 30-60 min; and for greater than 50 mm, it should be 1-2 h. Various types of electric furnaces are used for heat treatment of parts, and the furnace chamber must be thoroughly cleaned before treatment. When using gas or oil furnaces, the furnace atmosphere must be strictly controlled to maintain a slightly oxidizing atmosphere, and care must be taken to prevent the combustion nozzle from directly spraying onto the parts. Before vacuum annealing, the oxide scale and oxygen-rich layer on the surface of the parts should be removed, and the oil should be carefully removed before entering the furnace. For parts with complex shapes, clamps must be used for fixation during vacuum annealing to reduce deformation. Parts entering the furnace should ideally be filled with pre-degassed, oxide-free titanium dioxide shavings to prevent oxidation.
Surface treatment processes include shot peening to improve the fatigue strength of titanium alloy parts. Shot peening typically uses steel shot with a diameter of 2-5 mm, generating a surface compressive stress of approximately 785 MPa and a surface strengthening depth of about 200 μm. Shot peening significantly improves the fatigue strength of Ti-6Al-4V titanium alloy. To improve the wear resistance of Grade 5 titanium alloy, refractory particles such as tungsten carbide and chromium carbide are applied to easily worn parts, such as the damping platform sides of fan blades, using plasma or explosive spraying methods. This method can also be used to repair worn parts of titanium alloy components. To prevent scratches and adhesion of titanium alloy parts during operation, parts with frictional contact and threaded connections should undergo anodizing, chrome plating, electroless nickel plating, or nitriding treatments.
