Bronze does not have one fixed chemical formula. For anyone asking what bronze is made of, it is a family of copper-based alloys, not a single chemical compound with a constant atomic ratio. Traditional tin bronze is often summarized as copper and tin—sometimes about 88% copper and 12% tin—but that figure cannot represent every industrial bronze. Leaded bronze, aluminum bronze and manganese bronze have very different compositions and uses. For a bushing or bearing project, the complete grade matters more than a general percentage.
What Is the Chemical Formula for Bronze?
A formula such as H₂O describes a compound with elements bonded in a fixed ratio. Bronze is produced by mixing copper with controlled amounts of tin, aluminum, lead, zinc, nickel or other elements. The percentages vary by alloy grade, so there is no universal formula of bronze or formula for bronze.
Cu-Sn is useful shorthand for the copper-tin alloy system, but it is not a molecular formula for every bronze product. Even within tin bronze, different grades contain different amounts of tin and may also include lead or zinc. A specification such as UNS C90700 or C93200 is therefore more useful than writing only “CuSn” or “bronze.”
Bronze Composition Percentage: Why the Ratio Varies
The familiar 88% copper and 12% tin answer describes one possible high-tin bronze composition. It is a helpful introduction, not a universal manufacturing recipe. Industrial bronze alloy compositions are designed around different combinations of wear resistance, strength, machinability, corrosion resistance and casting behavior.
| Alloy and grade | Main composition by weight | Typical direction |
|---|---|---|
| Tin bronze C90700 | Cu 88–90%; Sn 10–12% | Heavy-load, relatively low-speed bearings, gears and wear parts |
| Leaded tin bronze C93200 / SAE 660 | Cu 81–85%; Sn 6.3–7.5%; Pb 6–8%; Zn 1–4% | General bushings, thrust washers and sliding components |
| Aluminum bronze C95400 | Cu 83% minimum; Al 10–11.5%; Fe 3–5%; Ni 1.5% maximum | High-strength bushings, gears and wear parts |
| Manganese bronze C86300 | Cu 60–66%; Zn 22–28%; Al 5–7.5%; Fe 2–4%; Mn 2.5–5% | High-load, low-speed bushings and heavy-duty components |
These examples also show why commercial names can be misleading. C86300 is commonly called manganese bronze, although its composition is based largely on copper and zinc rather than the traditional copper-tin system. Buyers should check the full designation, applicable standard and casting condition before treating two materials as equivalents.
How Alloying Elements Affect Bronze Bushings
Each element changes the balance of properties rather than adding one isolated benefit.
- Tin generally increases hardness, strength and wear resistance, but higher content can reduce ductility and make machining more demanding.
- Lead improves machinability, conformability and resistance to seizure. It can also reduce strength, and lead restrictions may apply.
- Aluminum supports high strength, hardness and corrosion resistance. The resulting alloy may require more demanding casting and machining control.
- Nickel and iron can improve strength and performance in selected aluminum bronze grades.
- Zinc affects strength, castability, cost and material classification in several commercial bronzes.
More alloying content is not automatically better. Load, speed, lubrication, shaft hardness, clearance, temperature and environment must be considered together.
Why “Bronze” Is Not Enough on a Bushing Drawing
A drawing that states only “bronze” leaves several important decisions unresolved. C93200 may suit a lubricated bearing that needs machinability and anti-seizure behavior, while C95400 may be considered for higher strength or impact. Neither grade is a direct substitute for the other.
For an accurate review, specify the alloy designation and standard, casting condition, required composition limits, mechanical properties or hardness, finished dimensions, tolerances and inspection documents. If the grade has not been selected, provide the load, movement, lubrication, shaft material, temperature and working environment. These details allow the material and manufacturing route to be evaluated together.
How JEDBUSHING Verifies Bronze Composition
JEDBUSHING manufactures custom bronze bushings and machined copper-alloy parts from drawings or confirmed samples. Before melting, the required grade is checked against the order and production documents. Metallic raw materials are prepared for the specified composition, and the molten batch is sampled and tested with spark optical emission spectrometers before release for casting.
Each batch is connected to a furnace number and production record, and furnace samples are retained for three years to support traceability. Depending on the purchase requirements, material certificates, composition records, hardness results and dimensional inspection reports can be discussed. This control is important because a finished part can look like bronze while still failing to meet the required grade. Learn more about JEDBUSHING’s copper-alloy melting and composition control.
Need a Custom Bronze Bushing?
JEDBUSHING produces tin bronze bushings, leaded bronze bushings, aluminum bronze bushings and other custom copper-alloy bushings, rings, wear plates and special-shaped parts. Casting, CNC machining, oil-groove machining and dimensional inspection can be arranged according to the drawing and order requirements.
Send the part drawing, required material, quantity and working conditions. If the drawing says only “bronze,” our team can review the application information and discuss a suitable material direction before quotation. Final material requirements should be confirmed before production.
FAQs About Bronze Composition
Can an old bronze bushing be identified by its color?
Not reliably. Different bronze and brass grades can look similar, while oxidation, oil and service wear can change the surface. Check original documents or use appropriate material testing before confirming a replacement grade.
Are similar bronze designations from different standards interchangeable?
Not automatically. UNS, EN, DIN and other systems may use compositions or product conditions that appear similar but are not identical. Compare the complete standard, chemical limits, mechanical requirements and casting form.
Can a replacement bushing be made when the original grade is unknown?
The project can be reviewed from the sample, dimensions, mating parts and operating conditions. Material testing may help identify the alloy family, but the final grade and acceptance requirements should be approved before production.
Does the casting method matter if the chemical composition is correct?
Yes. Centrifugal, continuous, permanent-mold and sand casting can produce different structures, soundness and mechanical properties. The drawing should identify the required specification and casting condition when these factors are critical.
