Cadmium‑Free Silver Brazing Filler Metals for Tungum to Stainless Steel Joints Update to legacy BS 1845 AG1 / AG2 filler metals

Tungum Technical Bulletin 1

Background

Historically, silver brazing alloys specified under BS 1845 such as Grade AG1 and AG2 were widely used for joining Tungum tubing to stainless steel fittings in hydraulic and instrumentation systems. These alloys contained cadmium (Cd), which improved fluidity and reduced brazing temperature. Due to health and environmental concerns associated with cadmium fumes during brazing, modern standards and industry practices have moved toward cadmium‑free silver brazing alloys.

Modern Standards

BS 1845 has been superseded by international brazing filler metal standards including EN 1044 and ISO 17672. These standards classify cadmium‑free silver brazing alloys primarily in the Ag‑Cu‑Zn‑Sn system, which provides excellent wetting and mechanical performance while eliminating cadmium.

Recommended Cadmium‑Free Filler Metal

The preferred modern filler metal for brazing Tungum to stainless steel fittings is:

ISO 17672: Ag156 | EN 1044: AG102 | AWS A5.8: BAg‑7

Typical composition (wt%):

• Silver (Ag): 56%

• Copper (Cu): 22%

• Zinc (Zn): 17%

• Tin (Sn): 5%

Melting range: approximately 620–655 °C.

Advantages of Ag156 (BAg‑7)

• Excellent wetting of both copper alloys and stainless steel

• High joint strength and fatigue resistance

• Good corrosion performance in marine and hydraulic environments • Comparable brazing temperature and flow characteristics to legacy AG1/AG2 alloys

• Eliminates cadmium exposure during brazing

Typical Brazing Practice

Recommended joint clearance: 0.05–0.15 mm (0.002–0.006 in)

Flux: Fluoride‑borate silver brazing flux suitable for stainless steel

Brazing temperature: approximately 650–750 °C

Heating technique: Heat the fitting first and allow the filler metal to flow into the joint by capillary action.