Bronze is made of copper and tin. This copper-tin base is what separates it from brass, which uses zinc as the secondary metal. A standard reference composition is 88% copper and 12% tin, and that tin content is why bronze resists wear and saltwater corrosion better than pure copper.
What Bronze Is Actually Made Of
Bronze's two-metal foundation is copper and tin, a combination that appears consistently in supplier references and material guides. Industry references usually describe bronze as primarily a copper-tin alloy; the Baosheng brass-vs-bronze guide, for example, gives a typical composition of 88% copper and 12% tin. That 88-12 split is not arbitrary: the same guide places January 2026 LME prices at about $13.34 per kilogram for copper and $53.46 per kilogram for tin, which explains why bronze typically costs 40–60 percent more than brass. The expensive ingredient is tin, and what you pay for with that premium is a structural change in how the alloy behaves. In saltwater, high-zinc alloys are prone to dezincification, and the guide notes that over 30% of marine hardware failures still trace back to that failure mode. Bronze's copper-tin matrix avoids that problem, which is why the two metals are not just a random recipe but a deliberate performance choice for components that face friction and corrosion.
The most common confusion about bronze is that it contains zinc, but that is the defining characteristic of brass. Knowledge-base comparisons of the two alloys put it plainly: brass is a copper-zinc alloy, while bronze is primarily a copper-tin alloy. This distinction matters far beyond a trivia question. When a supplier lists a red metal as 'bronze,' you are getting a material built for wear and corrosion resistance; when it lists 'brass,' you are getting a copper-zinc material that machines more easily and costs less. A manufacturing guide published in August 2025 reinforces the point, noting that bronze offers superior wear and corrosion resistance, greater hardness, and higher strength, while brass is ideal for parts that need excellent machinability and a bright gold finish. That is why valves and decorative hardware are often brass, while bearings and marine fittings are bronze. Keeping the two straight is not pedantic—it is the difference between specifying the right material and discovering months later that a component failed because it was cast from the wrong alloy.
Once you know the base pair, the natural next question is why tin, of all elements, is the one that gets added to copper. After all, copper alone is ductile and conductive; adding a small percentage of tin changes that behavior in ways that make the alloy useful for heavy-duty parts. The answer lies in how tin interacts with the copper crystal structure, and that mechanism is where the performance difference actually comes from. Understanding that mechanism also explains why not all bronzes feel the same, and why alloy families exist rather than a single recipe.
The Tin Effect on Bronze Performance
Tin changes copper by disrupting the soft, ductile crystal lattice of pure copper and replacing it with a tougher, harder structure. Source materials on CNC machining and application guides describe bronze as the best anti-friction, wear-resistant option among the red metals, with alloy C93200 often cited as a standard example. The mechanism is straightforward: tin atoms are larger and introduce distortions that make it harder for dislocations to move through the metal, which translates to higher strength and better resistance to surface wear. At the same time, the copper-tin matrix forms protective oxide layers that stand up to saltwater and chemical exposure far better than either pure copper or copper-zinc alloys. That is why marine hardware and bearings are almost always bronze rather than brass. Industry references from machining guides make the contrast explicit: selecting the wrong red metal for a CNC part is not a minor design error—it can cause catastrophic component failure, such as electrical connectors overheating or marine fittings seizing due to saltwater corrosion. The tin addition is what pushes copper from a workhorse conductor into a structural alloy.
Not all bronzes are the same, though: the tin percentage is only one variable, and commercial alloys add phosphorus, lead, or other elements to fine-tune properties for specific jobs. The Fraser Alloys table, which appears in industry reference material, lists several ASTM bronze specifications and shows how composition shifts performance. For example, C90700 is described as a phosphor bronze with good machinability, high strength, and good corrosion resistance, suitable for heavy-duty gears and bearings with medium to high loads. C83600, a leaded gunmetal, offers excellent machinability, medium strength, good pressure tightness, and is not subject to dezincification. C84400 is similarly easy to machine and is widely used in the pump industry for bowl and lineshaft bearings. The differences are not academic: increasing tin content generally makes bronze harder and more corrosion-resistant but also more brittle and harder to machine. Adding lead improves machinability but reduces strength slightly. So when you specify 'bronze' on a drawing, you are specifying a family of alloys, not a single metal, and the right choice depends on whether you need wear resistance, machinability, pressure tightness, or all three.
Because tin is the expensive driver, the cause-and-effect chain is direct: higher tin content buys more hardness and corrosion resistance but adds cost and machining difficulty. The Baosheng guide's cost data shows tin at roughly $53.46 per kilogram against copper at $13.34, which is why 12% tin in an 88-12 bronze adds real money to every bar. That is why manufacturers do not use the maximum tin content for everything; they match the tin level to the service condition. A bearing that sees high loads and saltwater gets a higher-tin bronze, while a decorative part might use a lower-cost alloy with less tin or even a brass substitute. The result is that 'bronze' is an engineering decision, not a fixed material.
Bronze in the Real World: Where the Tin Matters
Real-world applications are where the tin content earns its keep. In CNC machining, bronze is the default for bearings, bushings, and heavy-duty gears because its wear resistance and anti-friction properties keep parts alive under constant sliding contact. A 2026 machining guide on brass versus bronze explains that the choice is not about naming a 'better' metal; it is about matching the alloy to what the part will actually do. Bronze's superior wear resistance and durability make it the right call for load-bearing and corrosion-prone components, while brass shines in high-volume parts with tight tolerances and fine cosmetic finishes. The guide also points out that tool wear, cycle time, surface finish, scrap risk, and cost per part all change when you switch from brass to bronze. In a bearing housing, the bronze part may cost more upfront, but it avoids premature failure that would shut down a production line. That trade-off is exactly why engineers spend time on composition rather than just picking the cheapest bar.
The cost comparison between bronze and brass is stark, and the Baosheng guide quantifies it with 2026 LME data. Bronze is typically 40–60% more expensive than brass because tin costs several times as much as zinc. In January 2026, tin was about $53.46 per kilogram and zinc only $3.31, so every percentage point of tin in bronze adds cost. But that premium buys a property you cannot easily retrofit: resistance to dezincification. The guide's own numbers show that over 30% of marine hardware failures still trace back to high-zinc alloys in saltwater—so the right bronze can outlast a cheaper brass part where it matters most. For a machinist choosing stock material for a bearing housing, the decision is not about the sticker price alone; it is about what the part has to survive. If the housing sits in a wet or high-friction environment, the tin-based alloy is the lower-cost choice over the life of the assembly.
A practical selection tip: before you decide between brass and bronze, define the service environment and the failure mode you are trying to avoid. If the part lives in a high-wear bearing or a saltwater fitting, choose a bronze alloy with enough tin to handle the load—such as a phosphor bronze like C90700 for gears. If the part is a valve body or a decorative component that needs easy machining and does not face corrosive stress, brass will cost less and cut faster. Industry references on material selection consistently steer you toward matching properties to the environment, not to the color of the metal. When in doubt, ask your supplier for a comparison of candidate alloys in the same bearing or gear duty.
Buying Bronze: Find Your Alloy at Online Metals
Once you know which bronze alloy you need, sourcing becomes the next step, and Online Metals is one supplier that carries bronze as a distinct product category. The Online Metals site lists bronze among its selectable materials, alongside aluminum, brass, copper, and carbon steel, and its reference section includes guides on working with metal and understanding materials. Their customer service line, (888) 527-3331, is reachable for questions about stock, and the company ships metals, plastics, and raw materials directly. For a machinist or engineer, that means you can order a specific alloy without waiting on a traditional metal service center. The category listing itself is a confirmation that bronze is treated as a standard stocked material, not a specialty item, which makes it easier to compare suppliers and get consistent specs.
Choosing the right bronze at the point of sale means looking at the alloy designation, not just the word 'bronze.' The Fraser Alloys table used in industry references is a good model: alloy C83600, with its excellent machinability and pressure tightness, suits pump bearings; C90700, with high strength and good corrosion resistance, works for heavy-duty gears; C86300, a manganese bronze, offers exceptional strength and good wearing properties but only fair machinability. Online Metals carries multiple bronze alloys and lets you search by standard or specification, which is exactly what you need when a drawing calls out a specific ASTM grade. Ask for the material test report or mill certificate if your application is safety-critical, and confirm the tin content if you are paying a premium for corrosion resistance. That level of detail turns a simple purchase into a spec-controlled decision.
The verdict is straightforward: bronze is copper plus tin, and that tin addition is the reason it wins in bearings, gears, and saltwater environments. When you compare bronze and brass, the difference is not aesthetic—it is a trade-off between cost and durability. Bronze costs more because tin costs more, but it resists dezincification and wears longer. For any component that faces friction, pressure, or corrosive moisture, the tin-based alloy is the defensible engineering choice. Brass remains the sensible option for easy machining and low cost in benign environments. Choose by specifying the alloy, not just the name, and you will get the performance your drawing promised.
