Gold alloys casting

The grain size, surface roughness, and hardness properties of the gold alloys are not onlyexistence of alloy elements but also due to the applications of thermal and mechanical. Inrecent times, during the production of gold jewellery by casting, the proper annealingtemperature and duration parameters the heat treatment gains more importance. Thereduction of the raw gold alloy to a minimum level, improvement of mechanicalproperty, prediction of the optimum deep-drawability, easy polishing, improved stressproperty, and less crack occurrence during the pressing are well known propertiesobtained from a semi-finish gold alloy after the prediction of proper annealingtemperature and duration. For the preparation of the 22 carat yellow gold alloy, 91.6%Au, 4.6% Cu, 3.6% Ag and 0.2% Zn by weight alloy were used and the specimens weretaken from the semi-finish alloy at the end of the casting process. All melting process wascarried out by EIA trade-mark F9-s coded induction oven in the melting process sectionof Atasay Jewellery Company. The 22 carat yellow gold alloy was poured into the mould,preheated to 500 ºC. This casting process was utilized by blowing flame to the metalsurface and blower unit to prevent the air contact and decrease the viscosity of the liquidsurface of the metal. After casting the 22 carat gold alloy, it is located in 10% H2SO4solution to prevent from oxidation. The cooling process was carried out by water. Tomake the thickness of the alloy to be thinner from 5000 micron to 500 micron, a series ofrolling and annealing process were applied. It was analyzed by optical and electron-microscope. The specimens, allocated for the micro structure analysis, were polished bymetallographic technique and fired with 13% HCl HNO3 solution. The hardness of thespecimens was carried out by Vickers hardness measurement device. Besides this, deepdrawing tests were used for the deep-drawability of the specimens. The optimum 22 caratyellow gold alloy was obtained at the end of annealing temperature of 700ºC andduration time of 20 min among the numerous of annealed specimens at differentannealing temperature and duration. From this alloy the minimum re-crystallized grainsize and maximum deep-drawability were obtained.Key Words : Gold, Casting, Jewellery, AlloyAdviser: Prof.Dr.Ahmet EKERIM Date : 5/6/2006Jury Prof.Dr. Mustafa CIGDEM Page 58Jury Prof.Dr.Aysegul AKDOGAN