Oxide scale and rust formed during forging and heating treatment of all titanium alloys α The shell is brittle and induces cracks in subsequent forging or final forging or tool wear in subsequent machining. Therefore, it is best to remove rust and rust between continuous forging α The shell layer, and the rust and rust must be removed before the forging is delivered to the user α Shell.

　　The cleaning technology of titanium alloy forgings has two aspects: one is the removal of oxide scale; The second is α Removal of shell. The rust can be removed by mechanical methods, such as sand blasting; Or use chemical methods, such as melting salt derusting method. The choice of rust removal method depends on the size, complexity and cost of parts.

　　Sand blasting is an effective method to remove rust scale. It can remove 0.13 ~ 0.76mm thick rust scale. 100 ~ 150 mesh zirconium sand or steel sand can be used, and the air pressure can reach 275pa. Although sand blasting can be used for forgings of various sizes, it is mostly used for medium and large titanium alloy forgings. The sand blasting equipment can adopt the roller equipped with abrasive, shot blasting or sand blasting device. Pickling shall be carried out after sand blasting to remove α Shell.

　　Dissolving salt to remove rust is another effective method to remove oxide scale, which is also removed by pickling α Shell. I. flow chart, solution composition and relevant parameters of rust removal and pickling with dissolved salt. The racks used for dissolving salt and derusting are generally wooden, titanium or stainless steel, so as to prevent the electric potential between the workpiece and the rack from generating electric erosion or arc to the workpiece. Dissolved salt derusting is often used for medium and small forgings. In the case of large quantities of forgings, the operating system can be fully automated.

　　Pickling is used to remove rust α Shell, the process is as follows:

　　(1) Overall cleaning with sand blasting or alkali salt.

　　(2) If alkali cleaning is used, it shall be fully cleaned in clean flowing water.

　　(3) Pickling in sand acid hydrofluoric acid aqueous solution for 5 ~ 15min. The solution contains 15% ~ 40% HNO3 and 1% ~ 5% HF, and the operating temperature is 25 ~ 60 ℃. General acid content (especially for α+β and β Alloys) usually take the middle value of the above acid content range (e.g. 30% ~ 35% HNO3, 2% ~ 3% HF, or the ratio of HNO3 to HF is 10:1 to 15:1). However, the chemical solution with HNO3 and HF of about 2:1 can achieve the removal effect of 0.025mm/min, and the hydrogen absorption is the least.

　　When mixed acid is used, the content of titanium in acid solution increases continuously, so that the pickling effect decreases. It is generally considered that the titanium content of 12g / L has reached the maximum limit. If it exceeds this value, the solution shall be discarded. The solution can be treated by filtration or adding other organic chemical additives to prolong the service life of the acid washing solution.

　　(4) Clean forgings thoroughly in clean water.

　　(5) Wash with hot water to accelerate drying. Let it dry after washing.

　　The time required for metal removal and cleaning in pickling is mainly determined by α The shell thickness, the operation conditions of pickling tank, the needs of process and technical conditions and the trend of hydrogen absorption of workpiece are determined by several factors. Pickling provides conditions for excessive hydrogen absorption of titanium alloy, so it must be carefully controlled. The metal removal rate in pickling is generally 0.03 mm / min or more, which is strongly affected by the following factors, such as alloy type, acid concentration, solution temperature and titanium content. The metal removal thickness of each surface is up to 0.25 ~ 0.38mm, which is usually sufficient for removal α Shell. However, sometimes more or less clearance may be required, depending on the type of alloy and the specific conditions of the forging being processed.

　　Hydrogen absorption can reach 10% for every 0.03mm surface metal removed in pickling × 10-6, which depends on the specific pickling solution and concentration temperature conditions in pickling α Alloy ratio（ α+β) The hydrogen absorption trend of the alloy is small, but（ α+β) Alloy ratio β The trend of hydrogen absorption in pickling increases with the decrease of metal removal rate (due to the increase of titanium content in solution) and with the increase of cleaning temperature (higher than 60 ℃) Generally speaking, under a certain solution concentration and temperature, the metal removal rate must exceed the hydrogen diffusion rate. After cleaning, if the hydrogen content exceeds the maximum allowable hydrogen content of 140 ~ 170cm3 / 100g in the forging, it is necessary to increase vacuum dehydrogenation annealing.

　　The parts that do not need pickling shall be painted in advance for protection. However, it should be noted that the hanger holding the parts can only contact the parts coated with paint.