Precious Metal B628
GB B628
ASTM B628 covers the 72Ag-28Cu eutectic composition, which combines a low, sharply defined melting point with good conductivity and hardness.
Reference datasheet — B628 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the O condition
B628 tempers and conditions
B628 is supplied in 9 conditions, soft to hard. O is the default FabDigit quotes; the values on this page are for it.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ODefault Annealed | Choose for maximum ductility: deep-drawn contact rivets, stamped bimetal contacts and braze preform forming. | 130 | 280 | 25 | 62 HB | 87 % IACS |
Quarter hard | Use where slightly better stiffness and cut-edge quality are needed but forming is still severe. | 250 | 330 | 18 | 81 HB | 86 % IACS |
Half hard | Balanced temper for stamped contact blanks that still need moderate bending. | 320 | 390 | 12 | 95 HB | 85.5 % IACS |
Full hard | Most common hard temper for sliding contacts, slip rings and commutator segments requiring wear resistance. | 420 | 460 | 6 | 114 HB | 85 % IACS |
Extra hard | Pick when higher yield strength is required and only gentle forming radii are involved. | 480 | 510 | 4 | 128 HB | 84.5 % IACS |
Spring hard | Standard hard temper for flat springs, brush strips and wear-loaded contact faces. | 530 | 600 | 3 | 142 HB | 80 % IACS |
Extra spring hard | For thin strip and fine wire where stiffness and dimensional stability outrank any forming ability. | 620 | 680 | 2 | 156 HB | 78 % IACS |
Strain hardened, quarter hard | Contact springs and reed blades needing high elastic limit together with silver-class conductivity. | 640 | 660 | 2 | 170 HB | 83 % IACS |
Strain hardened, half hard | Highest strength temper for fine drawn wire and very thin spring strip; essentially unformable. | 690 | 710 | 1.5 | 180 HB | 83 % IACS |
What is B628?
ASTM B628 covers the 72Ag-28Cu eutectic composition, which combines a low, sharply defined melting point with good conductivity and hardness. It is used both as a brazing filler and as an electrical contact material, supplied as strip, wire and clad stock in tempers from O through H14; typical values are 280 MPa tensile, 130 MPa yield, 25 % elongation, 62 HB (30 HRB), 87 % IACS, 360 W/m·K and service to about 300 °C. The alloy tarnishes in sulphur-bearing air and cannot be anodized. Where higher elongation and a fully standardised rivet stock are wanted, ASTM B617 (90Ag-10Cu) is the nearest alternative. B628 has a density of 10 g/cm³ (0.361 lb/in³), lighter than 65% of precious metal grades. It melts at 779°C (1,434 °F). B628 has a yield strength of 130 MPa (18.9 ksi) and a tensile strength of 280 MPa (40.6 ksi) — weaker than 72% of precious metal grades. Elongation at break is 25% and the elastic modulus is 92 GPa (13.3 Msi).
What is B628 used for?
- braze-clad contact tips
- vacuum brazing of contact assemblies
- relay contact overlays
Advantages
- Conducts heat well — 360 W/m·K (208 BTU/hr·ft·°F), better than 94% of precious metal grades
- High electrical conductivity — 87 % IACS, better than 93% of precious metal grades
- Easy to machine — 55/100, better than 86% of precious metal grades
B628 properties
Typical room-temperature values for B628-O; bars are the position among precious metal grades.
Physical3
B628 has a density of 10 g/cm³ (0.361 lb/in³), lighter than 65% of precious metal grades. It melts at 779°C (1,434 °F).
Mechanical14
B628 has a yield strength of 130 MPa (18.9 ksi) and a tensile strength of 280 MPa (40.6 ksi) — weaker than 72% of precious metal grades. Elongation at break is 25% and the elastic modulus is 92 GPa (13.3 Msi).
Thermal6
B628 is rated for continuous service to 300°C (572 °F). It conducts heat at 360 W/m·K (208 BTU/hr·ft·°F), better than 94% of precious metal grades. Thermal expansion is 18.5 µm/m·K (10.3 µin/in·°F).
Electrical3
B628 conducts electricity at 87 % IACS, better than 93% of precious metal grades.
Chemical & Environmental3
Corrosion resistance is very good (72/100), worse than 66% of precious metal grades.
Sustainability4
Producing a kilogram of B628 takes about 1,100 MJ of energy and emits 105 kg of CO₂ — less than 71% of precious metal grades. Typical recycled content is 60%.
Manufacturability8
B628's machinability is good (55/100, better than 86% of precious metal grades); weldability good (55/100); formability excellent (90/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the precious metal family
Yield strength against density for every precious metal grade FabDigit runs. B628 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with B628
Is B628 easy to machine?
Machines like soft copper — gummy in the annealed state; use sharp positive-rake carbide, high speed, light feed and oil mist, and collect all chips for silver recovery.
Can B628 be welded?
Rarely fusion welded; contacts are attached by resistance welding, laser welding or by using the alloy itself as the braze at 780–850 °C in reducing atmosphere or with white flux.
Can B628 be formed, bent or molded?
Annealed strip stamps, coins and deep-draws readily; interanneal at 600–650 °C after roughly 50–60 % cold reduction to restore ductility.
B628 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Ageutectic silver content | 71.85 – 72.15 | 72 |
| Other (total impurities)Pb, Bi, Fe, O and similar tramp elements held low to protect ductility and arc behaviour | ≤ 0.15 | — |
| Cu | balance | — |
What surface finishes work on B628?
Polishes to a mirror; not anodizable — protect against sulfide tarnish with hard-gold flash, rhodium or an anti-tarnish lacquer for storage.
Equivalent designations
Standards and trade names that resolve to Precious Metal B628 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Also called
- 72Ag-28Cu Eutectic
How much does B628 cost?
B628 is a high-cost precious metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
B628 — frequently asked
What is B628 used for?
B628 is typically used for braze-clad contact tips, vacuum brazing of contact assemblies and relay contact overlays. In short: eutectic Ag-Cu braze and contact; lowest-melting Ag-Cu composition; 87 % IACS with 62 HB.
What is the yield strength of B628?
B628 has a typical yield strength of 130 MPa (18.9 ksi) and a tensile strength of 280 MPa (40.6 ksi) — weaker than 72% of precious metal grades. Strength varies by condition: see the 9 listed tempers.
Is B628 easy to machine?
Reasonably — machinability is rated good (55/100, better than 86% of precious metal grades). Machines like soft copper — gummy in the annealed state; use sharp positive-rake carbide, high speed, light feed and oil mist, and collect all chips for silver recovery.
Can B628 be welded?
Yes — weldability is rated good (55/100). Rarely fusion welded; contacts are attached by resistance welding, laser welding or by using the alloy itself as the braze at 780–850 °C in reducing atmosphere or with white flux.
What surface finishes work on B628?
Polishes to a mirror; not anodizable — protect against sulfide tarnish with hard-gold flash, rhodium or an anti-tarnish lacquer for storage.
Can B628 be formed, bent or molded?
Annealed strip stamps, coins and deep-draws readily; interanneal at 600–650 °C after roughly 50–60 % cold reduction to restore ductility.
What is the maximum service temperature of B628?
B628 is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between B628-O and B628-H14?
O is the default condition — choose for maximum ductility: deep-drawn contact rivets, stamped bimetal contacts and braze preform forming. H14: highest strength temper for fine drawn wire and very thin spring strip; essentially unformable. Yield strength is 130 MPa in O versus 690 MPa in H14.
How much does B628 cost?
B628 is a high-cost precious metal ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM B628 Standard Specification for Silver-Copper Eutectic Electrical Contact Alloy — ASTM International (2021)
- AWS A5.8/A5.8M Filler Metals for Brazing (BAg-8) — American Welding Society (2019)
- ASM Handbook Vol. 2: Properties and Selection — Nonferrous Alloys and Special-Purpose Materials (precious metals & electrical contact materials) — ASM International (1990)
- ASM Handbook Vol. 3: Alloy Phase Diagrams (Ag-Cu system) — ASM International (1992)
- Silver-copper braze and contact alloy datasheets — Lucas-Milhaupt / Umicore / Materion (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.