When titanium alloy castings are processed by hot isostatic pressing, the internal pores can be bridged for the first surface pores. And generally, it will not affect the dimensional stability of cast titanium alloy rods, but the surface pores and the subsurface pores connected to the surface must be removed by grinding, repair welding, and polishing. Pores are one of the common defects in titanium alloy rod castings. The size of a single pore is generally no more than 2-3mm, and the small one can reach the micron or sub-micron level that is difficult to see with the naked eye. Pores are one of the sources of cracks in castings. After reducing the fracture and sandblasting of the combined gold castings, the titanium alloy castings must be pickled before the surface quality inspection. Before delivery, it is also best to carry out pickling so that the surface of the casting is clean and bright, which is convenient for judging the appearance quality and level of the casting. Corrosive pickling can be used to adjust the dimensional accuracy of the casting wall thickness. The corrosion rate of the new bath is generally o. oo 5-0.0077mm/min, the corrosion cutting ability of titanium castings can be up to 0.2-0.4mm. Therefore, in the time-corrosive pickling process, attention must be paid to the problem of hydrogen permeation to avoid hydrogen embrittlement fracture of titanium alloy castings in use. Therefore, the precision titanium alloy castings that have undergone corrosive pickling generally need to be vacuum-annealed later.
Hydrofluoric acid is the main component of the pickling solution, and it is one of the few chemicals that can effectively corrode titanium. The addition of nitric acid to the hydrofluoric acid pickling solution promotes the uniformity and stability of this chemical process. The pickling operation process is as follows: the titanium castings put into the plastic net basket are lifted by a lift, and then immersed in the pickling tank for pickling. The pickling time is about 3-5 minutes, and the humidity of the pickling tank should be controlled at 20-25°C. After the pickling is completed, the casting must be cleaned in water and then dried in a stream of hot air to maintain a uniform and shiny surface of the casting. In industrial production, plastic rollers can be used instead of net baskets to load castings, and they can be immersed in trough towels for pickling. The slow rotation of the ten rollers drives the castings to continuously agitate during the pickling process to prevent the gas generated by the reaction from forming bubbles and adhering to the surface of the castings so that the pickling process of the castings can be carried out evenly and efficiently.
