The Study Of The Color And Aging Mechanism Of 14 Karat Color Gold Alloy

Gold alloy is one of the most important jewelry material.Higher quality was inquired to the 14Karat color gold alloy with the developing of jewelry industry.The aim of this research is age-harding mechanism and color mechanism with 14Karat color gold alloy.Based on the Au-Ag-Cu alloy color phase diagram,by adding Zn,the most representative of the current 14 Karat Au-Ag-Cu-Zn color gold alloy was selected.After ageing at2,6,and 10h400℃,the microstructure and hardness of the alloy was investigated by means of optical microscopy,micro hardness testing,X-ray diffraction(XRD).The transformation process was analyzed and the age-hardening mechanism was discussed.As the same time,The chroma parameters L^* a^* b^* values were measured by the means of CM-2600d in artificial sweat test.And also the discoloration of the alloy was reseached and its discoloration mechanism was discussed.The chroma parameters L^* a^* b^* values were measured by the color measurement,with the gold alloy colour contrast interval:sample AC1,AC2,AC3, AC4 were green gold alloy,AC5,AC6,AC7,AC8,AC9,AC10,AC11 were yellow gold alloy,AC12,AC13,AC14 were red gold alloy.At the same time,the color parameters of the alloy a^* b^* values of curve fitting mathematical formula experience.The color parameters of L^* a^* b^* values change and its mechanism of discoloration have been reseached in artificial sweat test.in the early immersion,The color parameters of L^* a^* b^* values were more obvious changed,The L^* value the first increased and then decreased,The a^* value was continuing inreased,b^* value was first reduced and then increased.Because of electrochemical reaction of the immersed sample,in the early immersion,The layer with corrosion of ZnO and Cu₂O were rapid formated on the surface of the alloy,And the color of Cu₂O was red,It caused that The a^* value was inreased.and the b^* value was rapide reduced,More and more Cu₂O layer was generated with the immersion time,The a^* values was continue increased,The b^* value was also increased with ZnO dissolved,The L^* value was also reduced when Cu₂O was changed into CuO.The microstructure was reseached in the process of aging of the alloy.After 700℃2h solution treatment,the microstructure of rolling specimens consisted ofα₀ single phase of face-centered cubic crystal.The matrixα₀ phase underwent differentphase decomposition depending on ageing time and Constituents.At 2 hour aging,the matrixα₀ phase underwent a spinodal decomposition and transformed into theα'₀ modulation structure.The spinodal decomposition might take place by the help of Cu atoms migration with the aid of quenched-in excess vacancies.Early stage of ageing at 400℃,the matrixα₀ phase transformedα'₀ modulation structure. Increasing the ageing time,theα'₀ underwent AuCu I ordered phase,Age-hardening was effect on the alloy,And all theα'₀ underwent AuCu I ordered phase at last.