Metallurgical aspects and corrosion behavior of yellow low-gold alloys

Three copper-free type III yellow low-gold alloys (Ag-Au-In-Pd-Zn) were investigated. Microstructural analysis was performed with x-ray diffraction, light microscopy, and an electron x-ray micro-analysis. The electrochemical behavior of the alloys was tested with standard potentiodynamic techniques in 0.9% saline solution and an artificial saliva and compared with that of a traditional high-gold alloy. The three alloys turned out to be two-phase mixtures of a fcc (matrix) and a bcc (island) phase. The yellow color, present in spite of the low-gold content, was caused by the disordered Pd-In, island-type structure. An additional third structure was seen after etching. However, no distinct phase could be correlated with it. The corrosion behavior for the experimental alloys, based on cyclic polarization, can be considered acceptable in both electrolytes used, but is inferior to that of the control alloy.