I have taken interest in an alloy of 97% silver and 3% copper as its properties are very close to fine silver, the difference is that it’s hardness is only that of Annealed copper, or only 3/4 the hardness of sterling, around 50 Bhn. HoweverTheory and Practice of Goldsmithing mentions the alloy may be Hardened to over 100 Bhn Which is the Annealed hardness of some 18K yellow golds. Much, much harder.
How do I age harden this alloy? What temperature must I heat it to and for how long? Do I need a kiln to do so and if so, which one? How much can i expect to pay for this kiln?
This is where the ability of Argentium silver alloys to be hardened by a simple, low temperature heat treatment at about 570oF (300oC) really becomes an advantage—giving the opportunity to increase the hardness of an as-cast item to improve its wear characteristics, while retaining sufficient ductility to allow some final forming or setting processes.
at the bottom of the Rio Grande blog post there are two blue links to publications…the one by Cynthia Eid is a free pdf download. it has instructions for heat treating Argentium…one method uses a kitchen countertop toaster oven.
Here is another great link for heat treating metals.
it notes:
"Sterling Silver. It is recommended to solution treat sterling silver at 750°C to 760°C/1,382°F to 1,400°F for 30 minutes, quench immediately, and age for one hour at 300°C/572°F. The hardness of the sterling alloy can be effectively doubled with this process, from HV 60 in the fully annealed state to HV 120.
The only problem posed by this process is that the solution treatment temperature is above normal soldering temperatures for sterling, so only articles with no solder can be treated. Soldering after hardening sterling will over-age the material dramatically to the point of nullifying the hardening effort"
You can get around that by annealling all components first, solder it all together and then when you are complete before finishing, age harden in the kiln at the lower temperature.