Gold alloy with improved hardness

A 3N 18 carat yellow gold-based alloy, comprising in weight percent:

• at least 75% of gold;
• from 0.5% to 2.1% of an aluminium metal capable of forming at least one precipitate with gold;
• from 20% to 25% of at least one first additional metal having an ability to favor a stable face centered cubic (FCC) structure and to increase high temperature solubility of the aluminum metal in the gold;
• 0% to 0.5% of at least one component affecting fluidity and grain size refinement of the alloy;
• and
• at least one aluminium and gold precipitate comprising Al2Au5 forming an intermetallic compound which provides the alloy with more than 250 HV hardness so as to improve structural hardening of the alloy.

A method for obtaining a gold-based alloy with improved hardness, the method comprising:

• (i) heat treating a mixture comprising:
• 0.5% to 2.1% of aluminium;
• at least 75% of gold;
• 20% to 25% of at least one first additional metal having an ability to favor a stable face centered cubic (FCC) structure and to increase high temperature solubility of the aluminum in the gold;
• and
• 0% to 0.5% of at least one component affecting fluidity and grain size refinement,
• to a temperature between 650° C. and 700° C. to form a heat treated mixture;
• then
• (ii) rapidly cooling the heat treated mixture by ambient temperature hardening to form a cooled mixture;
• (iii) tempering the cooled mixture at a temperature of between 200° and 250° C. to form at least one aluminium and gold precipitate comprising Al2Au5, said at least one precipitate being capable of inserting into the FCC structure of the at least one first additional metal and forming an intermetallic compound capable of imparting a desired hardness of more than 250 HV to a resulting gold-based alloy;
• (iv) maintaining the tempering for at least 60 minutes to grow the intermetallic compound in a controlled manner to obtain the resulting gold-based alloy with the desired hardness;
• and
• (v) cooling the resulting gold-based alloy at ambient temperature.