Surface Treatment Process For Titanium Alloy Forgings

Titanium alloy forgings are the core components of titanium alloy products. Their surface quality directly affects the mechanical properties, corrosion resistance, and dimensional accuracy of the products, as well as the operational reliability and service life of equipment. The industry adopts a standardized four-step surface treatment process,such as sandblasting, defect repair, grinding, and coloring.

1. Sandblasting is the first step in the surface treatment of titanium alloy forgings. It mainly removes impurities such as oxide scale, sand adhesion, oil stains, and burrs from the workpiece surface, while forming a uniform rough surface to provide favorable adhesion conditions for subsequent processes and avoid defects such as poor bonding and quality inconsistencies.

2. High temperatures during titanium alloy forging generate a dense oxide layer, which impairs the adhesion of subsequent processes and reduces corrosion resistance, so it must be thoroughly removed. Sandblasting strips surface impurities through the impact and cutting action of high-pressure air-jet abrasives. Given the high chemical activity of titanium alloys, process parameters must be strictly controlled:

• White fused alumina is preferred as the abrasive; sandblasting pressure is controlled within 0.45 MPa;
• Sandblasting duration is 15–30 seconds, only cleaning surface impurities-residual reaction layers are handled by subsequent processes to prevent secondary pollution caused by improper parameter.       

3. After sandblasting, titanium alloy forgings feature a uniform pitted surface, qualified roughness, and enhanced surface activity, which strengthens the bonding strength between subsequent coatings and the substrate, laying a solid foundation for the entire surface treatment process.

1.This process is not forging forming casting, but a specialized procedure to repair micro defects such as blowholes, shrinkage cavities, and depressions left after sandblasting, level the surface, and enhance performance.

2.Titanium alloy has poor molten fluidity, large casting temperature differences, and a fast cooling rate. Even in a protective atmosphere, blowholes easily form inside and outside the forgings, which seriously degrade surface quality and mechanical properties and require targeted repair.

3.Repairs are performed using processes matched to defect types:

• Deep blowholes and shrinkage cavities are eliminated via hot isostatic pressing;
• High-precision forgings are first positioned by X-ray flaw detection, then laser repair welding is applied after grinding to expose the cavities;
• Shallow surface blowholes can be directly repaired by local laser welding to restore surface integrity and continuity.

After defect repair processing, surface defects of the forgings are completely eliminated, flatness is greatly improved, and grain structure is optimized at high temperatures to enhance mechanical properties, providing a flat and uniform base for subsequent grinding.

1.Grinding is the core process for improving the surface precision of titanium alloy forgings. It removes welding marks, micro protrusions, and residual impurities, reduces surface roughness, improves finish, releases surface stress, and enhances wear and corrosion resistance. Due to titanium alloy's high chemical activity, poor thermal conductivity, and tendency to adhere to abrasives, abrasive selection and process parameters must be strictly controlled.

2.Grinding is divided into two stages: rough grinding and fine grinding:

• Rough grinding uses 60–80# ceramic or zirconia corundum abrasive belts to trim obvious surface defects;
• Fine grinding uses 180–320# silicon carbide abrasive belts to refine surface finish. Ultra-high-precision forgings can add a polishing step ; high-end products adopt chemical mechanical polishing to achieve nanoscale surface processing.

3.Superhard abrasives such as diamond and cubic boron nitride are preferred for grinding to avoid chemical reactions with titanium alloys; polishing line speed is controlled at 900–1800 m/min to prevent surface burning and microcracks. After grinding, forgings have qualified finish, no scratches or protrusions, and uniform surface stress, ready for the final coloring process.

Coloring is the final step of surface treatment for titanium alloy forgings, serving both decorative and protective purposes. Through chemical or electrochemical methods, a transparent oxide film of varying thickness is formed on the workpiece surface, displaying colors such as golden yellow, purple, and blue. It also improves corrosion and wear resistance and extends service life.

1.The mainstream industrial method is anodizing, which is simple, eco-friendly, and produces an oxide film with strong adhesion, stain resistance, and corrosion resistance. The forging acts as the anode and stainless steel as the cathode, with constant-voltage oxidation in a specially formulated solution at 15–35 °C; colors can be customized by adjusting voltage and time, with different parameters producing golden yellow, purple, and other effects.

2.Alternative methods include surface nitriding and atmospheric oxidation. Nitriding produces a light golden color and further enhances surface hardness and wear resistance. After coloring, water washing and drying ensure the oxide film is dense and stable, preventing peeling and fading.

Ruihang Group mainly produces titanium products with the complete industry chain,including smelting,forging, straightening,rolling,surface treating,testing process. For any purchasing needs, feel free to contact us at email:Sam.Rui@bjrh-titanium.com