UNS C51000 bronze

Identity and purchasing scope

Concast lists 15% IACS at 20°C for C51000 containing 5% tin and 0.2% phosphorus. KME gives 10 MS/m (about 17% IACS) as typical at 20°C in the annealed condition. Keep the composition and temper bases with these figures and agree the conductivity test for the delivered stock. Concast physical-property footnote, KME typical annealed values

UNS C51000 is commonly identified as phosphor bronze 5% A. Concast's ASTM B139/B139M-12(2017)-based sheet lists Sn 4.20–5.80%, P 0.03–0.35%, Pb maximum 0.05%, Zn maximum 0.30%, Fe maximum 0.10%, copper remainder, with copper plus named elements at least 99.5%. “5% tin” is nominal shorthand rather than an exact composition requirement. Concast C51000 chemistry, p. 1

KME cross-references CuSn5, CW451K and C51000 for its rolled material. Use such references to locate candidate products, then confirm the required standard, form and delivered condition. A cross-reference does not establish that every heat or product meets all requirements of a particular purchase specification. KME CuSn5 sheet

Temper controls the strength/forming compromise

KME's EN 1652 rolled-product table lists these tensile intervals:

Its table separately distinguishes standard and bending-optimized properties and gives bend guidance for strip thickness ≤0.50 mm. Preserve those qualifiers rather than treating a radius or elongation entry as universal. KME mechanical and bend table

Select the delivered condition around the actual forming sequence and required finished force. Establish bend direction, radii, springback, burr direction and residual set in representative parts. Do not translate an R-condition to an H-condition using only a similar strength number. The applicable standard, product form and supplier agreement determine acceptance.

For mechanical design, keep tensile strength, proof/yield strength, hardness and elongation separate. A hardness check can support a defined acceptance plan; it does not automatically establish all mechanical properties or a finished spring's load-deflection curve. Define the completed part's allowable deflection, load, permanent set and dimensional requirements.

Fatigue and stress relaxation answer different questions

Wieland's B15 CuSn5/C51000 sheet describes fatigue strength in terms of 10⁷ cycles under symmetrical alternating bending, dependent on temper, and gives an approximate relationship to tensile strength. This is a bounded material description, not an infinite-life limit or an arbitrary spring's fatigue qualification. Wieland B15 fatigue definition, p. 2

For a cyclic component, establish stress amplitude, mean stress, geometry, finish, environment, temperature and target life. Evaluate the actual feature, including bends, edges and attachment regions. A catalog tensile minimum cannot determine fatigue life without an appropriate design basis. Do not turn a symmetric bending result into a contact-force or vibration guarantee for a different load history.

The same Wieland sheet presents thermal stress relaxation measured on stress-relief-annealed specimens parallel to rolling direction. It states that relaxation depends on applied stress and is increased to some extent by cold deformation. Wieland relaxation conditions

Keep this time-at-temperature behavior separate from cyclic failure. For a contact spring, define required retained force after the intended dwell, thermal cycles and assembly deflection. Test representative formed and finished parts when their processing differs from the supplier's specimen condition. A favorable short test or room-temperature spring force does not establish long-term contact performance.

Conductivity: retain composition and condition

Concast lists 15% IACS at 20°C, explicitly measured on an alloy containing 5% tin and 0.2% phosphorus, and warns that conductivity varies with composition. Concast physical-property footnote, p. 4

KME instead gives 10 MS/m, approximately 17% IACS, as typical annealed values at 20°C. Neither entry should be silently converted into a guaranteed minimum for every delivered C51000 temper. KME physical-property conditions

As an original calculation using KME's rounded conductivity, a uniform conductor 100 mm long with 1 mm² cross-section has R = L/(σA) = 0.1/(10 × 10⁶ × 10⁻⁶) = 0.01 Ω, or 10 mΩ, at the assumed material condition and temperature. This excludes contacts, plating and temperature rise. It is a bulk-resistance illustration, not a current rating or predicted assembled connector resistance.

Fabrication, joining and release

Concast rates C51000 cold-working capacity excellent, hot-forming capacity poor, and machining at 20; its soldering and brazing ratings are excellent. These are comparative fabrication descriptions, not process parameters or joint-strength guarantees. Concast fabrication table, p. 4

Qualify machining, stamping and deburring on the actual stock condition. Define edge quality and surface damage limits at highly stressed features. For joining, specify cleaning, filler/interlayer where applicable, thermal history and inspection. Determine whether heating alters the condition or force of nearby spring regions. Parent-stock properties do not establish finished-joint capacity.

Define corrosion exposure by substance, concentration, temperature, duration and contact conditions; “bronze” is not a blanket compatibility approval. For plated contacts, qualify the coating and substrate together. Retain grade, supplier/lot, form, temper, drawing revision and required inspection or test results. Review substitutions against mechanical, electrical and processing requirements together.

Sources reviewed November 1, 2026. Wieland's PDF prints 06.21. The cited KME and Concast PDFs provide no explicit printed publication/revision date; their filenames and website upload paths are not assigned as dates. Concast identifies its specific ASTM B139/B139M-12(2017) table basis; select the contract-required edition for actual procurement.

Related reference

Grades, conditions and material selection