(2) Precious metal brazing alloy is more resistant to corrosion. It is generally required to be etched with strong alkali, strong acid and strong oxidant to show the microstructure of the brazing material. The parent metal is non-precious metal material, which is not resistant to corrosion and is easily oxidized under the action of strong acid and alkali. In addition, the solder in the weld is as-cast, the structure is unstable, and the base metal is annealed, and the structure is relatively stable. In combination with these characteristics, the selection of the etchant should be able to display the microstructure of the brazing material faster without causing the parent metal to be oxidized and at the same time exhibiting its microstructure. Previous page EV LIGHT Guangzhou Co., Ltd , https://www.evlightpro.com
(3) In the electrolytic erosion method, since the brazing material and the base material at the brazing joint are simultaneously immersed in the electrolyte (etching agent) for electrolysis, the base material is a non-precious metal, the electrode potential is low, and the precious metal of the brazing filler is formed, and itself Consumed, so there is no clear weld metallography, generally not used
(4) When preparing the metallographic sample of the brazing joint of the precious metal brazing material, due to the complexity of the welded joint structure, different metallographic inlay powders or special jigs are required according to the specific conditions of the weldment. For softer alloy polishing, the speed of the polishing disc should be slow, if necessary, without polishing paste, try to make the surface of the weld smooth and smooth before it is eroded.
4 Conclusion
(1) In order to obtain a clear metallographic structure containing precious metal alloy brazing filler metal such as Au, Pd and Ag, the preparation of the metallographic sample should be chemically etched.
(2) In order to avoid excessive erosion (blackening) of non-precious metal base materials, weak etchants should be selected and the erosion time should be strictly controlled.
Preparation of metallographic samples of precious metal solder joints (3)