CuSn12 (EN CC483K) — the high-speed tin bronze

CuSn12 sits at the top of the tin bronze range, with roughly 11–13 % tin in a copper matrix. The high tin content raises hardness and wear resistance well above the CuSn8 and CuSn10 grades, and it does so without the soft lead phase that limits the load capacity of leaded gunmetals. The trade-off is that machinability and dry-running tolerance are poorer than Rg7.

It is the standard choice for machine-tool spindle bearings, worm wheels, piston-pin bushes and press bearings — applications that combine high surface pressure with high sliding speed and reasonably reliable lubrication.

Chemical composition — EN 1982 (castings), weight %

Mechanical properties — EN 1982, by casting route

Table 2 — CuSn12 mechanical minima per EN 1982. DIN 1705 (2.1052) lists broadly similar values; ingot and casting composition limits differ slightly between the two standards.

Key characteristics: high wear resistance, good cavitation resistance, good corrosion resistance including seawater, and the ability to sustain high surface pressures combined with shock loading. Hot and cold formability are both poor, so CuSn12 is used almost exclusively in cast and machined form.

 Rg7 / CuSn7Zn4Pb7 (EN CC493K) — the general-purpose gunmetal

If CuSn12 is the specialist, Rg7 is the workhorse. Known variously as gunmetal, red brass or bearing bronze — and in Germany as Rg7 or G-CuSn7ZnPb — it carries roughly 5–7 % lead as discrete soft particles dispersed through a tin bronze matrix. Those particles do two useful things: they break chips during machining, and they smear under boundary lubrication to give the alloy its well-known dry-running tolerance.

The lead content is also its limitation. Soft lead phases reduce fatigue strength and load capacity relative to CuSn12, so Rg7 is specified for medium rather than maximum loads. It is, however, the grade most often chosen where lubrication cannot be guaranteed.

Chemical composition — weight %

Table 3 — CuSn7Zn4Pb7 composition limits. The DIN 1705 column matches the values quoted in the source data sheet.

Mechanical properties — continuous cast (GC)

Typical applications include cylinder and bearing liners, gears, wear strips, pump impellers, water-pump shaft sleeves, diesel piston inserts, hydraulic press fillers and general sliding elements. Weldability is poor; soldering is acceptable.

 CuZn25Al5 (UNS C86300) — high-tensile manganese bronze

Despite the name, manganese bronze is not a bronze in the metallurgical sense. The dominant alloying element is zinc, at roughly 22–28 %, so the alloy is properly a high-tensile brass strengthened by aluminium, iron and manganese. The name persists because the alloy competes directly with true bronzes in bearing and wear service.

What C86300 offers is compressive strength. Typical continuous-cast tensile strength of 780 MPa and hardness of 210 HB put it well above the tin bronzes, and its compression deformation limit of 380 MPa minimum makes it suitable for heavily loaded, slow-moving bearing surfaces where the oil film is maintained.

Chemical composition — weight %

Table 4 — CuZn25Al5 composition. The controlled range column follows the source data sheet and aligns with JIS H5102 HBsC4; the ASTM column is shown for comparison. Note the tighter nickel limit in the controlled range.

Mechanical and physical properties — continuous cast

Table 5 — CuZn25Al5 mechanical and physical data. ¹ The source data sheet quotes a specific gravity of 8.2; the value of 7.83 g/cm³ is the CDA-published figure for continuous-cast C86300 and is the value recommended for weight and cost calculation. Confirm against the material test certificate.

C86300 is supplied as continuous cast bar and tube, centrifugal cast tube, and sand castings. Foundry behaviour needs care: casting yield is low, drossing is high and solidification shrinkage is high, so melt cleanliness and a properly designed feeding system matter. Soldering, brazing and gas welding are not recommended; coated metal arc welding is rated good.

CuAl10Ni5Fe4 (UNS C63000) — nickel aluminium bronze

Nickel aluminium bronze is the alloy to reach for when a bearing or wear part has to survive load and seawater and elevated temperature at the same time. Around 10 % aluminium forms a tenacious alumina film that resists erosion, cavitation and impingement attack; nickel and iron add strength and toughness.

Chemical composition — ASTM B150 C63000, weight %

Mechanical properties — ASTM B150 / AMS 4640, HR50 condition

Table 6 — Section-dependent minima. Hardness is typically 201–248 HB up to 50.8 mm section and 187–241 HB from 50.8 to 127 mm.

Designation cross-reference

Cross-referencing copper alloys between standards is an exercise in approximation. Composition windows overlap but rarely coincide, and the casting or working route is frequently different. The table below is intended for identification and sourcing, not as a statement that one designation may be substituted for another in a qualified design.

Table 7 — Identification cross-reference for commercial supply. “Comparable” indicates similar but not identical composition. EN 12163, EN 12165, EN 12167 and EN 12420 cover wrought forms of the aluminium bronze grades; EN 1982 covers castings.