Titanium alloys are mostly required to be surface treated during heat treatment and after heat treatment in order to remove oxide scale and various contaminants on the metal surface, reduce the activity of the bare metal surface, and coat the protective layer and various functions of titanium and its alloys. The surface treatment is also carried out before and during the coating process, and the coating is applied to improve the properties of the metal surface, for example, to prevent corrosion, oxidation and abrasion.
The pickling conditions of titanium and its alloys are determined by the type and characteristics of the oxide layer and the existing reaction layer, and the type of this layer is affected by the high temperature heating process and the temperature increase of the processing process (for example, forging, casting, welding, etc.). . Only a thin oxide layer is formed at a lower processing temperature or a heating temperature of about 600X: or less, and an oxygen-rich diffusion region is formed in the vicinity of an oxide layer under high temperature conditions, and must also be eluted by acid. In addition to this oxygen-rich diffusion layer. Various methods for removing scale can be employed: a mechanical method for removing a thick oxide layer and a hard surface layer, a scale for removing the scale in a molten salt bath, and an acid stripping and descaling in an acid solution.
In many cases, a combination of several methods may be employed, for example, mechanically removing the scale and then pickling, or first removing the scale by a salt bath followed by pickling. In the case of an oxide layer and a diffusion layer formed at a relatively high temperature, a special method is employed, but an oxide layer formed by heating at a high temperature to 600X: is mostly dissolved by a general pickling.