Select silver brazing alloys by base metal, melting range and process: AWS BAg, ISO 17672, GB/T grades, Cd-free options, preforms.
Base metals — Cu-P self-fluxes on copper but is excluded from steel/stainless/nickel (brittle phosphides); Zn/Cd grades are poor on stainless in wet service.
Joint & clearance — 0.05–0.13 mm (0.002–0.005 in); controlled-atmosphere silver 0.038–0.051 mm. Narrow-interval (BAg-8) fills tight repeatable joints; wide-interval (BAg-22/13a/23) tolerates irregular gaps and positional brazing.
Heat source — torch: flux-compatible rod; induction: ring/preform/paste; furnace: paste/preform; vacuum: bare only, never flux; H₂/inert: Li grades.
Form & documents — preplaced rings/preforms turn deposit variance into a dimensional tolerance.
AWS | Ag-Cu-Zn + others | Solidus/Liquidus °C (ISO/EN codes in §5)
2.1 Ag-Cu-Zn BAg-5 45-30-25 665/745 default Cu/brass/steel · BAg-6 50-34-16 690/775 · BAg-9 65-20-15 670/720 · BAg-10 70-20-10 690/740 · BAg-20 30-38-32 675/765 · BAg-35 35-32-33 685/755
2.2 Tin-modified — core of Cd-free BAg-7 56-22-17, 5Sn 618/652 most specified Cd-free grade · BAg-36 45-27-25, 3Sn 640/680 · BAg-28 40-30-28, 2Sn 650/710 · BAg-34 38-32-28, 2Sn 650/720 · BAg-37 25-40-33, 2Sn 680/760 · Ag155 55-21-22, 2Sn 630/660 · Ag134 34-36-27.5, 2.5Sn 630/730
2.3 Ni/Mn-modified (Ni: wetting on W/WC, corrosion; Mn: wider interval, CTE) BAg-24 50-20-28, 2Ni 660/705 most specified Ni grade · BAg-4 40-30-28, 2Ni 670/780 · BAg-22 49-16-23, 4.5Ni 7.5Mn 680/700 carbide · BAg-13a 56-42, 2Ni 770/895 · BAg-13 54-40-5, 1Ni 720/855 · BAg-26 25-38-33, 2Ni 2Mn 705/800 · BAg-23 85Ag 15Mn 960/970
2.4 High-silver / controlled atmosphere BAg-8 72-28 779/779 eutectic, vacuum · BAg-8a 72Ag 0.25-0.5Li 766 · BAg-18 60-30, 10Sn 602/718 · BAg-19 93Ag 0.2Li 760/890 · BAg-21 63-28.5, 6Sn 2.5Ni 690/800
2.5 Silver-bearing Cu-P (self-fluxing on Cu only) BCuP-2 0Ag 710/793 · BCuP-6 2Ag 645/788 · BCuP-3 5Ag 645/815 · BCuP-7 5Ag 645/785 · BCuP-4 6Ag 645/718 · BCuP-5 15Ag CP102 645/802 · BCuP-8 18Ag 643/666
Cd lowers liquidus and widens the working window: metallurgically effective, compliance-heavy. EU: prohibited since Dec 2011 (Reg. 494/2011); RoHS 0.01%. US: OSHA ventilation/respiratory protection indoors unless air testing complies. End uses: water, food, medical and consumer goods commonly exclude Cd.
BAg-1 Ag345 45-15-16, 24Cd 605/620 · BAg-1a Ag350 50-15.5-16.5, 18Cd 620/640 · BAg-2 Ag335 35Ag 19Cd 605/700 · BAg-2a Ag330 30Ag 21Cd 600/690 · BAg-3 Ag351 50-15.5-15.5, 16Cd 3Ni 630/690 · BAg-27 25Ag 13.5Cd 605/745 · BAg-33 Ag326 25Ag 17.5Cd 605/720 · Ag340 40Ag 20Cd 595/630 lowest solidus
Cd→Cd-free conversion: record current qualification → select by temperature budget (BAg-1 has no like-for-like; BAg-7 closest low-temp, BAg-36 closest at 45Ag) → re-select flux (FB3-A ≈566–871 °C) → tighten clearance → trial coupons with sectioning/radiography → update declaration and SDS.
Priority matrix — A stock deep: BAg-7, BAg-5, BAg-24 · B common forms: BAg-36/28/37/6/8 (margin from ring dimension, wire tolerance, paste rheology) · C make-to-order + review: high-numbered and atmosphere grades · D legacy, screened: BAg-1/1a/2/2a/3/27/33 · Substitute: BCuP-6/5/3/7/4/8
BAg-7 — Cd-free + low temperature + broad base-metal coverage in one grade; 34 °C interval is predictable in induction and furnace cycles. Earns: lower peak temperature cuts annealing, distortion and cycle time. Loses: not a vacuum alloy; wrong for large carbide, high-temperature or chloride service.
BAg-5 — the grade most legacy 45% silver drawings mean; Cd-free, gap-forgiving, two-directional (upgrade from BAg-20/35, cost-down from BAg-6/7). Loses: Zn-bearing on wet/chloride stainless; 745 °C too hot for thin parts.
BAg-24 — Ni wets stainless, nickel alloys and WC more reliably with a more corrosion-resistant interface; lowest-melting common Ni grade. Earns: fewer reworks, less porosity around tungsten, lower tool reject rates; sticky once qualified. Loses: costlier than BAg-5.
BAg-8 / BAg-8a — eutectic: sharp freeze front, fills 0.038–0.051 mm, high conductivity, no flux, no residue, no cleaning line. Earns: in vacuum the cost drivers are cycle time, yield and cleaning, not metal per kg. Loses: highest exposure to silver price; Ag-Cu can penetrate OFC grain boundaries.
BAg-36 — 45Ag at ~680 °C: BAg-5 silver content, lower liquidus, same metal cost.
BAg-28 / BAg-37 — volume cost-down grades; needs consistent clearance and no Ni-grade corrosion demand.
BCuP-5 / BCuP-6 — in Cu-to-Cu HVAC&R phosphorus self-fluxes: no flux purchase, application or residue removal, lower cost/kg.
Joint-cost model — per acceptable joint = filler (g) × alloy unit cost + flux/atmosphere + energy & cycle time + labour/automation + inspection + expected rework/leak/scrap − recovered scrap. Higher silver can be cheaper per joint where it removes a cleaning step or lifts first-pass yield. Preforms and metered paste cut placed-mass variance.
Silver price — quote a conversion charge plus an alloy surcharge indexed to a benchmark date.
AWS, ISO 17672, EN 1044, GB/T 10046 and JIS Z 3261 are classification groups, not automatic interchangeables; exact match requires agreement on chemistry, tolerances, impurity limits, solidus/liquidus, form and scope.
BAg-5↔Ag245/AG203↔BAg45CuZn · BAg-6↔Ag250↔BAg50CuZn · BAg-7↔Ag156/AG102↔BAg56CuZnSn · BAg-8↔Ag272/AG401↔BAg72Cu · BAg-8a↔Ag272Li · BAg-9↔Ag265 · BAg-10↔Ag270 · BAg-18↔Ag160↔BAg60CuSn · BAg-20↔Ag230 · BAg-21↔Ag463 · BAg-22↔Ag449/AG502↔BAg49CuZnMnNi · BAg-23↔Ag485↔BAg85Mn · BAg-24↔Ag450↔BAg50CuZnNi · BAg-28↔Ag140↔BAg40CuZnSn · BAg-34↔Ag138 · BAg-36↔Ag145/AG104↔BAg45CuZnSn · BAg-37↔Ag125↔BAg25CuZnSn · BAg-13↔Ag454 · BAg-13a↔Ag456 · BAg-1↔Ag345↔BAg45CuZnCd · BAg-1a↔Ag350 · BAg-2↔Ag335 · BAg-2a↔Ag330 · BAg-3↔Ag351↔BAg50CuZnCdNi · BCuP-5↔CP102 · BCuP-6↔CP105
Two traps: legacy HL numbers are not specifications — one number can mean Cd or Cd-free; an equivalence chart is a substitution proposal — verify solidus/liquidus and Cd/Ni/Mn/Sn limits first.
Cd lowers liquidus, widens the window and gives surface-tension behaviour that travels into narrow, unevenly heated joints. Sn lowers the melting range and improves ferrous wetting but shifts phases toward Cu-Sn/Ag-Cu-Sn, changing flow, oxidation, gap-filling and post-braze corrosion. BAg-7 melts below BAg-5 yet is not a drop-in; conversion means higher peak temperature, new flux, tighter clearance, re-qualification.
Industry HVAC&R: BCuP-6/5/3; BAg-5/7/36 for steel transitions · Electrical: BAg-6/8/7/24/21 · Contacts: BAg-7, BAg-24, BCuP-8 · Automotive: BAg-5/6/7/36 · Carbide: BAg-24, BAg-22, BAg-13a · Aerospace: BAg-8/8a/19 · Food/water: BAg-5/6/7/24 · Vacuum: BAg-8/8a/18 · Jewellery: BAg-7/28/36/37
Forms rod · wire (diameter, cast) · flux-coated rod · flux-cored wire (never vacuum) · ring (OD/ID, gap) · washer/preform (flatness, burr) · strip/foil · paste (rheology, shelf life) · powder
Flux FB3-A ≈566–871 °C · FB3-C longer/hotter cycles · FB4-A difficult oxides. Match the active window to actual peak temperature and dwell, not to solidus. Remove residue — it sustains crevice corrosion on stainless. Never flux a vacuum cycle.
Defects voids → placement, flux, oxide, gap · beading → oxide or burnt flux · erosion → excessive heat or dwell · brittle joint → P on ferrous/nickel · post-braze corrosion → residue, chlorides, Zn filler · carbide cracking → CTE mismatch
Documents CoC/MTR · EN 10204 3.1 vs 3.2 · RoHS with analytical scope · REACH/SVHC · SDS · dimensional inspection · origin · standard-edition declaration. Wording discipline: do not call the filler metal certified for potable water, food contact, medical or automotive use.
Copper to stainless? Cd-free; BAg-7 usually first, BAg-24 where Ni improves interface and corrosion; Cu-P excluded. Is BAg-7 a drop-in for BAg-1? No — different flow, gap tolerance, post-braze behaviour; needs new flux, clearance and inspection. Lowest melting? Cd-bearing BAg-1 ≈605–620 °C (restricted); Cd-free BAg-7 ≈618–652 °C. Can 72Ag cost less to use than 45Ag? Yes where it removes flux cleaning, shortens the cycle or lifts yield — per your line data. Can Cu-P replace silver? On Cu-Cu/Cu-brass often yes; on steel, stainless or nickel no. Are Cd grades still available? For legacy MRO where permitted; EU-banned since Dec 2011. Carbide tips? BAg-24 for small–medium; BAg-22/13a for a wider interval. Vacuum furnace? Bare forms only; BAg-8/8a/18/19. ISO equivalent of BAg-7? Ag 156 — confirm the Sn band.
Base metals · joint type, clearance · heating method, flux permitted? · current alloy and defect history · service environment · form, dimension, quantity · documents · destination market.
Next: grade confirmation · Cd-free conversion trials · joint-cost review · sample lot.
Typical values shown for chemistry and melting range are reference data compiled from published classification and manufacturer technical tables. They are not contractual specifications. Confirm the applicable standard edition, the chemical range and the lot analysis before ordering. Cadmium-bearing grades are supplied only where legally permitted; the buyer is responsible for verifying the regulatory position in the destination market and end use.