Trimetal brazing alloys combine the tensile properties of copper with the versatility of silver alloys and are an effective and reliable choice for carbide-to-steel brazing, such as in toolmaking. A trimetal shim is a three-layer design with two outer strips of brazing filler metal clad onto a copper middle in a 1-2-1 ratio.
The copper core makes the trimetal unique among alloys. Copper withstands high temperatures, resists corrosion, and is excellent for larger carbide applications that are prone to cracking or distortion due to differences in thermal expansion rates of base metals. The outer “jacket” consists of a combination of common filler metals such as:
- Silver (Ag) - Silver, the standard for non-ferrous and ferrous applications, provides versatility, high strength, and low melting points
- Nickel (Ni) and Manganese (Mn) - Nickel and Manganese aids in carbide wetting, corrosion protection, and strengthens the bond
- Cadmium* (Cd)- affords higher mechanical strength and a harder, more wear-resistant joint; can also be used at lower working temperatures
- Zinc (Zn) - used for its corrosion protection
Trimetal alloys are excellent for applications that require a filler metal to handle high stress and impact, like in the joining of carbide and steel for tooling tips.
| Product | AWS | AMS | Composition | Solidus | Liquidus |
|---|---|---|---|---|---|
| TRI40Ni2 | BAg-4 | - | AG 41.6% CU 30% NI 2% ZN 28% | 1240 F | 1435 F |
| TRI49Ni4 | BAg-22 | - | AG 50% CU 16% MN 7.5% NI 4.5% ZN 23% | 1260 F | 1290 F |
| TRI50Ni3 | BAg-3 | 4771 | AG 52% CD 16% CU 15% NI 3% ZN 15% | 1170 F | 1270 F |
| TRI50Ni2 | BAg-24 | 4788 | AG 52% CU 20% NI 2% ZN 28% | 1220 F | 1305 F |