In the field of metal material processing and application, heat treatment is a key process that plays a crucial role in improving material performance. Surface treatment is equally indispensable during and after heat treatment. This step aims to remove oxide scale and various contaminants generated on the metal surface, reducing the activity of the exposed metal surface. Surface treatment is especially essential before and during the application of protective layers and various functional coatings to titanium and its alloys. By applying these special coatings, the properties of the metal surface can be effectively improved, such as enhancing its corrosion resistance, oxidation resistance, and wear resistance, thereby extending the service life and range of the material. Titanium Home, as a well-known information platform in the industry, has been closely monitoring and reporting on the development of related process technologies for titanium rods and their alloys, providing timely and accurate information for industry professionals.
Factors Affecting Pickling Conditions of Titanium Rods and Their Alloys
The pickling conditions for titanium rods and their alloys are not static but depend on the type (characteristics) of the oxide layer and existing reactive layers. The types of these oxide layers are influenced by a combination of factors, with high-temperature heating and temperature increases during processing (such as forging, casting, and welding) being the primary factors.
The oxide layer formation on the surface of titanium bars and their alloys varies significantly under different processing temperatures. At lower processing temperatures, or at high heating temperatures below approximately 600°C, only a thin oxide layer forms on the metal surface. This thin oxide layer is relatively easy to remove and has little impact on subsequent processes. However, the situation becomes more complex at high temperatures. At high temperatures, not only does an oxygen-rich diffusion zone form near the oxide layer, but this oxygen-rich diffusion layer also has a significant impact on the material's properties and subsequent processing. It must be completely removed through processes such as pickling to ensure that the material's surface quality meets requirements.
Multiple Methods for Oxide Scale Removal
To effectively remove oxide scale from the surface of titanium bars and their alloys, the industry employs various methods, each with its own applicable scope and characteristics.
Mechanical Methods
Mechanical methods are mainly suitable for removing thick oxide layers and hard surface layers. This method removes oxide scale from the metal surface through physical actions such as friction and impact. Its advantages include relatively simple and direct operation, and it can quickly and effectively remove most of the thick and hard oxide scale. However, mechanical methods also have limitations. For example, the process may cause some mechanical damage to the metal surface, affecting its smoothness and finish. Furthermore, for parts with complex shapes and high precision requirements, mechanical methods may not achieve the desired results.
Molten Salt Bath Method
Removing oxide scale in a molten salt bath is another commonly used method. Titanium rods and their alloys are immersed in a specific molten salt bath. The high temperature and chemical action of the salt bath cause the oxide scale to separate from the metal surface. This method can treat the metal surface more uniformly and is well-suited for parts with complex shapes. Moreover, by rationally selecting the composition and process parameters of the salt bath, the processing can be controlled to a certain extent, reducing damage to the metal substrate. However, the molten salt bath method also has some drawbacks, such as high equipment investment, the need for strict control of temperature and salt bath composition during operation (otherwise, the treatment effect may be affected), and the environmental pollution risk associated with molten salt baths, requiring corresponding environmental protection measures.
Acid Solution Pickling
Acid solution pickling is one of the most commonly used methods for removing oxide scale. By immersing titanium rods and their alloys in a specific acid solution, the chemical reaction between the acid and the oxide scale dissolves it, thus achieving the purpose of removal. The pickling method has advantages such as high processing efficiency, relatively low cost, and flexible operation. For oxide scales of different types and thicknesses, the optimal treatment effect can be achieved by adjusting parameters such as the type, concentration, temperature, and pickling time of the acid solution. For example, oxide layers formed at high temperatures up to 600℃ can mostly be dissolved by general pickling. However, the pickling method also has some issues that need attention. Acid solutions are corrosive; improper operation may cause excessive corrosion to the metal substrate, affecting the material's performance. Furthermore, the pickling process generates waste acid and other pollutants, which need to be properly treated to avoid environmental harm.
Application of Combined Methods
In actual production, several methods are often combined to remove oxide scale, fully utilizing their advantages to achieve better processing results.
For example, mechanical methods can be used first to remove most of the thicker, harder oxide scale, followed by pickling. This method combines the rapid removal capability of mechanical methods with the fine processing capability of pickling. It can quickly reduce the thickness of the oxide scale first, and then pickling further removes residual fine oxide scale and impurities, while causing relatively little damage to the metal surface and achieving a better surface quality.
Another common combination is to first perform a salt bath treatment, followed by pickling. Salt bath treatment can soften the oxide scale to a certain extent, weakening its adhesion to the metal surface, while also providing preliminary cleaning and activation of the metal surface. Then, pickling can more thoroughly remove the oxide scale and improve pickling efficiency, reducing pickling time and acid solution usage.
When encountering oxide layers and diffusion layers formed at higher temperatures, due to their complex structure and properties, special methods are required for treatment. These specialized methods may be improvements and optimizations of the aforementioned conventional methods, or they may be entirely new processes developed for specific situations. For example, they may require specially formulated acid solutions or multi-step processing flows, precisely controlling the process parameters at each step to ensure complete removal of the oxide and diffusion layers while maintaining the quality of the metal surface.
In summary, the surface treatment and pickling process for titanium rods and their alloys is a complex and crucial process. Understanding the factors influencing oxide layer formation, rationally selecting oxide removal methods, and combining multiple methods according to actual conditions are of great significance for ensuring the surface quality of titanium rods and their alloys, improving their performance, and meeting the needs of different application fields. In actual production, it is necessary to continuously explore and optimize process parameters and improve process technology to achieve high-quality processing and application of titanium rods and their alloys.
