Preparation and Properties of Trivalent Chromium/Zirconate Composite Conversion Coating on Al-50%Si Alloy

Al-50%Si alloy is a mainstream electronic packaging material. In order to solve the problem of high corrosion resistance on the surface of Al-50%Si alloy and reduce environmental pollution, a trivalent chromium/zirconium salt composite conversion coating was developed for the package shell without acid-base washing and spraying. The appearance, surface morphology, composition, and corrosion resistance of the conversion coating were characterized and analyzed by visual inspection, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and neutral salt spray test. The results show that the prepared trivalent chromium/zirconium salt composite conversion coating is composed of amorphous particles. After treatment, the content of Zr element on the surface of Al-50%Si alloy increases to 3.63%, Cr element increases to 0.82%, and oxygen content increases to 9.21%; after 168 hours of neutral salt spray test, there is no obvious corrosion on the surface of the conversion coating.