To define the optimum heat treatment temperature and time of the developed three types of low karat gold alloys, hardness test, DTA and x-ray diffraction methods were used.
The results were as follows.
· The optimum temperature of heat treatment was at 400C in K- I , K-H and K- Hl alloys.
· The proper time of age-hardening was 10 minute in K- I alloy, and 10-30 minutes in K-Ⅱ and K-Ⅲ alloys.
· The stable phases of three types of low karat gold alloys were Ag-rich a 1 phase, Cu-rich a 2 phase and AuCu I phase in case of K- I alloy, and a 1 phase and AuCu I phase were coexisted in K-11 and K- III alloy.
· The cause of the decrease of hardness by overageing was the a 1 phase and AuCu I phase, which were precipitated in the grain boundary.
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