The surface of zirconium rod and hafnium alloy must be clean and bright before joining, heat treatment, electroplating and forming. Generally speaking, no special surface treatment and cleaning are required for corrosion resistance, because zirconium naturally forms a metal oxide protective layer regardless of the surface conditions. Zirconium is difficult to be electroplated by traditional methods, but it can be electroplated by special processes.
1, surface decontamination
Grease, grease, and lubricants produced by machining or other processes can be removed in a number of ways. The widely used cleaning methods include cleaning with alkali or emulsion cleaner in the soaking tank, cleaning with ultrasonic vibration, washing with acetone or trichloroethylene or steam degreasing and cleaning with other cleaners. To lighter filth, can use a few solvents to be like acetone, alcohol, trichloroethylene or trichloroethylene substitute to wipe purify with the hand, also can use electrolytic alkali decontamination method. In the electrolyte system, if voltage and current can be controlled to avoid anodic polarization or spark discharge and pitting corrosion, positive polarity or negative polarity can be used to decontaminate. Surfaces must be cleaned prior to heat treatment and joint to prevent metal contamination and the resulting ductility deterioration.
2. Spray cleaning
Mechanical decontamination methods such as sand blasting, shot peening, and evaporation can remove dirt and lubricants from zirconium and hafnium surfaces. Alumina, silicon carbide, silica and steel particles are ideal materials for mechanical decontamination. The used decontamination medium should be replaced regularly to avoid the increase of workload caused by particle passivation.
Polishing or shot-blasting may result in residual compressive stress and thermal deformation on the surface of materials, especially on the surface of thin plates. Thermal deformation may also occur during subsequent rolling and contour machine runs.
Spray cleaning is not a substitute for pickling. Spray cleaning cannot remove the surface layer contaminated by interstitial elements such as carbon, oxygen and nitrogen. In general, after the spray cleaning and pickling, to ensure the complete removal of surface contamination and cold working layer, to get a smooth, shiny metal surface.
