In the process of galvanizing iron parts, in addition to the electrodeposition of zinc, there are often side reactions of hydrogen ion reduction and hydrogen evolution.
After hydrogen reduction, part of it becomes gas and escapes, and part of it penetrates into the lattice of the coating and matrix metal in the form of hydrogen atoms, causing lattice distortion, increasing internal stress of parts, and embrittlement of the coating and matrix, which is called hydrogen embrittlement.
Hydrogen embrittlement does great harm to the mechanical properties of materials. If it is not removed, it will affect the service life of parts and even cause damage accidents of machines. Therefore, some steels or parts used under special conditions must undergo dehydrogenation treatment. For example, galvanized parts used in aircraft must undergo dehydrogenation treatment. Hydrogen removal is also required for galvanizing on elastic parts and high-strength steel.
The hydrogen removal adopts heating treatment to drive the hydrogen out of the parts. The dehydrogenation effect is related to the dehydrogenation temperature and holding time. The higher the temperature is, the more thorough the dehydrogenation will be. However, the heating temperature should not be too high. If it exceeds 250 ℃, the crystalline structure of zinc is deformed and brittle, and the corrosion resistance is significantly reduced. Generally, L90 ℃ ~230 ℃, 2h~3h. The hydrogen removal temperature of carburized parts and tin weldments is 140 ℃ ~l60 ℃, and the heat preservation is 3H.
In any electroplating solution, due to the dissociation of water molecules, there is always a certain number of hydrogen ions more or less. Therefore, in the process of electroplating, the precipitation of metal at the cathode (main reaction) is accompanied by the precipitation of hydrogen (side reaction).
The influence of hydrogen evolution is multifaceted, the most important of which is hydrogen embrittlement. Hydrogen embrittlement is one of the most serious quality hazards in surface treatment. Parts with serious hydrogen evolution may break during use, causing serious accidents. Surface treatment technicians must master the technology to avoid and eliminate hydrogen embrittlement, so as to minimize the impact of hydrogen embrittlement.
