2003 Volume 44 Issue 4 Pages 504-510
Microstructures in coated magnesium alloy with high purity magnesium fabricated by applying a vacuum deposition technique were investigated. Moreover, relationships between microstructures in coated and un-coated magnesium alloys and corrosion behaviors were interpreted by in-situ laser microscopic observations during salt immersion tests. Magnesium with 3N-grade and AZ31 magnesium alloy were used for an evaporation source and a substrate for deposition. Temperature of the substrates was changed resulting in change in temperature profile in a furnace in order to optimize deposition coating conditions for obtaining homogeneous microstructures and thickness in deposited layer. The coated specimen revealed superior corrosion resistance to those on 3N–Mg, AZ31 and AZ91E alloys, and comparable to that on 6N–Mg in salt immersion tests using 3% NaCl solution at 300 K for 587 ks. In-situ observations showed that inhomogeneity in microstructures, such as second phases and grain boundary segregations, deteriorate corrosion resistance in magnesium alloys. Therefore, pure magnesium coated layer without inhomogeneity in metallographic and electrochemical meanings can improve the corrosion resistance on magnesium alloys.