Aluminum Bronze for Bearings and Bushings

Aluminium bronze is what gets specified once a tin bronze lining is no longer enough: loads two to three times higher, temperatures that soften ordinary bronzes, impact and edge loading, and seawater. The aluminium builds a hard, strong copper matrix, and the nickel-bearing grades add heat-treatable strength on top of it. The price is a hard, galling-prone surface that demands the right shaft pairing, and a family whose property spread is wide enough that the grade name alone does not define the material.

the low-aluminium and silicon-bearing wrought grades, the iron-bearing wrought and cast grades, the nickel aluminium bronzes, and the heat-treatable high-strength grades. Sources: CDA alloy database, ASTM B148/B150/B271/B505, EN 1982, EN 12163/12167/12420, GB/T 1176, GB/T 5231.

Grades in this family

Twenty grades are compared here. Sixteen of them carry aluminium as the principal alloying addition; the remainder are included because supplier catalogues routinely group them under the same heading, and because they are frequently offered as substitutes. Both cases are flagged in the table rather than quietly omitted, since a substitution made on a catalogue heading rather than on a composition sheet is how wrong material reaches a bearing.

Four sub-families, and what separates them

The family is most easily read as four bands defined by what has been added to the copper-aluminium base. Understanding the band tells you the property direction before any number is consulted.

Low-aluminium and silicon-bearing (C60600, C60800, C64200)

Below roughly 8 % aluminium the structure is a single phase, which keeps the alloys ductile and cold-formable but modest in strength. Two of these grades exist for reasons other than load: C60800 carries arsenic to suppress selective corrosion in water service, and C64200 carries silicon, which improves machinability while retaining the aluminium oxide film that gives the family its corrosion behaviour. Where a part must both resist a marine atmosphere and be produced in volume from bar, C64200 is the grade that resolves the conflict.

Iron-bearing, wrought and cast (C61300, C61400, C61900, C62300, C62400, CuAl10Fe3, CuAl9Mn2)

Iron is the workhorse addition. It refines the grain, forms hard iron-rich particles that raise hardness and abrasion resistance, and pushes the aluminium level at which a second phase appears. This is the band that does the general engineering work of the family: valve and pump parts, worm wheels, bushings, wear plates and structural hardware. Its limit is not strength but corrosion under flow: the iron-bearing grades resist seawater less well than the nickel-bearing ones, and where the service involves velocity, entrainment of solids or cavitation, the next band up is the appropriate move.

Nickel aluminium bronze (C63000, CuAl10Ni5Fe4, C63200, C95400, C95500, C95800, CuAl9Fe4Ni4, CuAl9Ni3Fe2)

Nickel changes the character of the alloy. It stabilises a fine, complex microstructure, improves the tenacity of the surface oxide, and raises strength without the loss of ductility that a straight increase in aluminium would bring. Nickel also makes several of these grades heat-treatable, which separates them from the iron-bearing band. The distinguishing behaviour is under flow: resistance to impingement attack, cavitation erosion and crevice corrosion in seawater is the reason this band exists, and it is the reason stern-tube bushes, pump shafts, propellers and seawater valve trim are specified here.

Heat-treatable, high strength (C63020, CuAl11Fe6Ni6)

The final band raises aluminium to 10-12 % with nickel and iron both around 5-7 %. In a controlled quench-and-temper condition these grades deliver the highest strength and hardness in the family. They are also the least forgiving: ductility falls to single digits, notches become crack sources, and machining cost rises. They are specified sparingly, where a calculation has already shown that the standard grades are not sufficient.

Composition

Single values are maxima, except where a minimum is marked. Ranges reflect the published limits of the standard cited for each grade; individual standards differ slightly, and a drawing that names a standard takes precedence over this table. C65100 is listed for the reason given in Table 1 and carries no aluminium.

Mechanical properties

The properties below are grouped by product form and condition, because in this family the form and the heat treatment move the numbers by more than the grade does. Read the “basis” column before comparing two rows: a published minimum for continuous cast product and a typical value for wrought bar are not the same kind of number, and placing them side by side without that distinction is the most common error in material comparison tables.

Values marked “minimum” are standard minimum requirements for the condition shown; routine production usually sits above them. Values marked “typical” are published representative figures and are not the values to be expected from a specific lot. Yield strength is quoted at 0.2 % offset for wrought product and at 0.5 % extension under load for cast product, which is one of the reasons the two sets of numbers should not be compared directly.

Three patterns hold across the table. Tensile strength rises from about 400 MPa in the low-aluminium band to 750-910 MPa in the heat-treatable band, while elongation falls from 35-55 % to 5-8 %. Nickel, not aluminium, is what buys corrosion performance, so grades with comparable strength and different nickel content are not substitute materials. And the iron-bearing cast grades reach their properties as cast, whereas the nickel-bearing grades have a second, higher band available through heat treatment.

European designations and their minima

European purchasing documents describe these alloys by short designation, not by UNS number, so a comparison table that stops at the C-number is incomplete for anyone buying or selling inside the European market. The table below gives the EN short designation, the corresponding EN material number where one is assigned, and the published minimum properties. The numbers are useful for a second reason: they show how much the casting route matters within one designation.

Cross-references marked “related” are comparable, not identical. Two cases deserve particular care. First, the cast designation CC333G is CuAl10Fe5Ni5-C, the nickel-bearing cast grade; it is not the counterpart of the iron-bearing CuAl10Fe3, which maps to CC331G. Second, CuAl10Ni5Fe4 as a Chinese wrought designation (QAl10-4-4) and as an EN designation (CW307G) describe closely similar chemistry but come from different standard systems, and their contractual property requirements are stated differently. Confirm against the standard named on the drawing before substituting one for the other.

Casting route and heat treatment

Two process decisions move the properties of a finished aluminium bronze bush by more than the choice between neighbouring grades. Both should therefore appear on the drawing, and neither always does.

The casting route

Continuous and centrifugal casting solidify the metal against a cooled mould or a spinning wall, giving a finer structure with less porosity than a sand mould, and the published minimum properties differ accordingly. For C95400 the continuous cast minimum tensile strength is 586 MPa against 517 MPa for sand cast product; for C95800 the same comparison across the sand to centrifugal range spans 586-655 MPa. The spread can reach 10-40 % on tensile strength depending on the grade, larger in the tin bronzes than in the aluminium bronzes. A drawing that names only the alloy therefore leaves an important part of the material undefined. Name the alloy and the casting route, or state the property requirement and let the foundry choose the route that reaches it.

Heat treatment

C95500, C63020 and the CuAl10Ni5Fe4 and CuAl11Fe6Ni6 families are heat-treatable: a solution treatment near 900 °C, followed by a controlled quench and a temper, rearranges the phases and lifts yield strength well above the as-cast figure. Three practical consequences follow, and they apply to the works order, not to the design office:

• Higher allowable stress. Heat-treated nickel aluminium bronze supports bush designs that would run an as-cast iron-bearing grade over its yield limit.
• Distortion control. Heavy castings move during the quench. Leave machining allowance for final dimensioning after heat treatment rather than before it.
• Weld repair policy. A welded repair to a heat-treated part requires re-heat treatment or a documented alternative. Decide the policy before the weld, not after it, because the decision changes the repair route and the delivery date.

Heat treatment is not a default. The as-cast iron-bearing grades already outperform most tin bronzes, and where the calculated stress sits comfortably inside the as-cast yield limit there is nothing to gain from the additional process step and its distortion risk.

Seawater, cavitation and temperature

The nickel aluminium bronzes are the marine grades, and the reason is not static corrosion rates but behaviour under flow. Nickel stabilises a tenacious, self-repairing surface oxide that resists impingement attack, cavitation erosion and crevice corrosion. Under static immersion the difference between an iron-bearing and a nickel-bearing grade is modest; under a pump impeller, a propeller wake or a silt-laden stern tube, it becomes the deciding factor.

• Stern tubes, rudder bearings and pump shafts. C95800, CuAl9Fe4Ni4 and C63200 are used for the bushings in these positions, and also for the housings around a nickel aluminium bronze shaft, so that the two parts are galvanically compatible.
• Cavitation and silt erosion, not static corrosion, set the life of marine sliding parts. A duty cycle with frequent stops, starts and part-load running generates more cavitation damage than a steady high-speed one. Assess the duty, not just the environment.
• Freshwater and process water. C60800 and C64200 are the water-side grades, the first for corrosion duty in tube and the second where a machined part is also needed. Neither is a heavy-load bearing material.

The galling question: shaft pairing

Aluminium bronze is hard, and against a similar hard surface under boundary lubrication it is prone to galling: asperity junctions form and tear rather than smear. This is the property that most often decides whether an otherwise correctly selected alloy works. Three rules follow from it.

• Pair with a hard, smooth steel shaft. A journal hardness of about 45-55 HRC and a ground finish in the region of Ra 0.2-0.4 µm is the customary pairing. A rougher or softer shaft accelerates both its own wear and the bushing’s.
• Never pair aluminium bronze against itself unless an anti-galling measure has been validated for the duty: a coating, an extreme-pressure grease, or an interposed lining.
• Embeddability is low. In dirty or abrasive service the alloy cannot bury contamination in a soft phase, so particles score the running surface. Clean lubrication or filtration is part of the specification, and where neither can be relied upon a leaded tin bronze or a graphite-plugged design survives better at lower load.

Where lubrication reliability is the problem rather than load, the practical answer is to keep the aluminium bronze base and change the lubrication mechanism: a graphite-plugged bushing carries the same matrix strength while supplying solid lubricant to the contact. That approach is treated in solid lubricant systems.

Load, speed and PV

Reference values, not design allowables. Catalogue PV figures for this family differ between suppliers by a factor of two or more, partly because some are quoted for oil or grease lubrication and others for dry running. Convert units before comparing: 1 N/mm²·m/min equals 0.0167 MPa·m/s. Halve the catalogue figure for a first-pass design, then derate further for elevated temperature, a soft or rough journal, contaminated lubrication, and oscillating rather than continuous motion.

Machining

Aluminium bronze machines in the general range of a medium-strength steel rather than of a free-cutting brass, and the published ratings reference free-cutting brass at 100: the iron-bearing grades sit around 30-60, with C64200 at the top of the family and C63020 at the bottom. Two consequences matter operationally.

• The ratings are comparative, not absolute. A rating in the 30s does not describe a difficult material in the sense that a superalloy is difficult. It describes an alloy that needs positive rake, sharp and correctly ground edges, no dwell in the cut, and a rigid setup.
• Work hardening and heat are the real constraints. Repeated passes over a work-hardened surface, or a rubbing tool, will consume edges quickly. A generous approach to depth of cut with flood coolant is more productive than light passes.

Two further points apply to finished bushings. Aluminium bronze responds to fine boring and roller burnishing, but a cutting process that leaves a smeared or torn surface will gall against the journal from the first revolution. And because the family is notch-sensitive at the higher-strength end, oil grooves and oil holes need radiused bottoms and generous edge breaks; a sharp-bottomed groove in a hard, low-ductility bronze is a fatigue crack waiting for a load cycle.

Selection guidance

Two notes that change the numbers

Related material pages

FAQ

What is the difference between C95400 and C95500?

Chemistry and heat-treatability. C95500 adds nickel at the cost of copper content and is supplied heat-treatable: solution treatment with a controlled quench and temper raises yield strength well above the as-cast figure. C95400 carries nickel only as a residual and is used as-cast, or in a heat-treated condition where a moderate further gain is needed.

Is C95800 a bearing material or a propeller material?

Both, in different roles. Its recognition comes from marine castings such as propellers, pump bodies and valve trim, but as a sliding material it serves stern-tube and pump-shaft bushings where seawater resistance and galvanic compatibility with a nickel aluminium bronze shaft matter. For pure load capacity, compare it against a heat-treated nickel aluminium bronze.

What is C63020 and when is it specified?

C63020 is the higher-alloy nickel aluminium bronze with roughly 10-11 % aluminium, 4.2-6.0 % nickel and 4.0-5.5 % iron, supplied in a heat-treated condition. It reaches the highest tensile strength and hardness in this family and is specified where the calculated stress or the wear duty is beyond what the standard grades hold in the as-cast condition. The trade-off is low ductility, notch sensitivity and the highest machining cost in the family.

Why do aluminum bronze bushings gall?

The hardness and the tenacious oxide film that give the family its strength and corrosion resistance also reduce its ability to smear and self-repair at asperity contacts. Against a hard counterface with a similar oxide under boundary lubrication, junctions form and tear. Mitigations are hardened and ground shafts, extreme-pressure greases, or a graphite-plugged variant of the same base alloy.

What separates C60800, C61300, C61400 and C62300?

Aluminium content and iron. C60800 is a 5-6.5 % aluminium grade with an arsenic addition for water service and is not intended as a bearing material. C61300 and C61400 carry 6-8 % aluminium with 1.5-3.5 % iron and sit in the middle of the family. C62300 raises aluminium to 8.5-10 % with 2-4 % iron and is the general-purpose bearing and valve grade.

Is C60600 still available?

C60600 is an inactive UNS designation, withdrawn in 1992. It is still found in older drawings and in catalogue reprints. Where it appears on a new order, C60800 or C61400 are the practical replacements, and the choice depends on whether the service is water-side corrosion or a bearing function.

Does the casting route change the properties of an aluminum bronze?

Yes, materially. Within one grade, continuous or centrifugal casting produces higher published minima than sand casting, because the faster solidification gives a finer structure with less porosity. The spread can reach 10-40 % on tensile strength depending on the grade, so a drawing should name the alloy and the casting route, or state the property requirement directly.

Does aluminum bronze need heat treatment?

Not by default. The as-cast iron-bearing grades already outperform most tin bronzes. Heat treatment is specified for the nickel-bearing grades when the calculated stresses approach the as-cast yield limit, or when the wear surface must run harder. Two consequences follow for the works order: leave machining allowance for movement during the quench, and settle the weld-repair policy before the weld rather than after it.