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Cast aluminum bronze is made by melting a controlled copper-aluminum-iron charge, filling a properly designed mold, and verifying the finished casting. A practical reference alloy is UNS C95400, commonly called 9C, with a nominal composition of approximately 85% copper, 11% aluminum, and 4% iron.
This is not an easy beginner foundry project. C95400 melts above 1,000°C (1,830°F), and water contacting molten metal can cause a violent steam explosion. The procedure below is therefore a process overview for a trained foundry operator working under a documented molten-metal safety procedure—not a substitute for foundry training, engineering controls, or a qualified metallurgist.
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Bronze is a family of copper-based alloys, not one fixed recipe. Aluminum bronze, silicon bronze, tin bronze, manganese bronze, and nickel aluminum bronze have different compositions, melting behavior, oxidation risks, and casting procedures.
This guide uses UNS C95400, a widely specified cast aluminum bronze often called 9C. The current Copper Development Association data for C95400 lists these composition limits:
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| Element | C95400 limit or balance |
|---|---|
| Aluminum | 10.0–11.5% |
| Iron | 3.0–5.0% |
| Manganese | 0.50% maximum |
| Nickel | 1.5% maximum |
| Copper | At least 83.0% |
A nominal working composition is approximately 85% copper, 11% aluminum, and 4% iron. That ratio is useful for understanding the alloy, but it is not proof that a casting meets C95400. Aluminum oxidation, dross losses, scrap contamination, and alloying-element recovery can all change the final chemistry.
For a safety-critical, pressure-containing, or specification-controlled part, use certified ingot or master alloy and verify the melt with spectrographic analysis. Do not identify the alloy by color, appearance, or the labels on unidentified scrap.
Before starting: equipment and safety requirements
Molten aluminum bronze requires equipment designed for copper-base alloys. A furnace suitable for aluminum is not automatically suitable for C95400. The alloy’s published solidus is approximately 1,027°C (1,880°F) and its liquidus approximately 1,038°C (1,900°F); the furnace must also provide sufficient controlled temperature for melting, transfer, and filling.
Use a crucible rated for copper alloys and compatible with the furnace, atmosphere, fluxes, and maximum temperature. Clay-graphite and silicon-carbide crucibles are commonly used for copper-base alloys, but selection should follow the crucible manufacturer’s guidance. The technical guidance from Foseco on matching a crucible to its application explains why metal, furnace type, temperature, atmosphere, and treatment materials all matter.
Control the work area with appropriate ventilation, guarding, lifting equipment, dry floors, a clear pouring path, emergency planning, and trained personnel. Foundry hazards include molten-metal splash, radiant heat, metal fumes, gases, vapors, silica, and explosive steam releases. CDC foundry safety material discusses these hazards, while OSHA’s eye and face protection standard covers protection against molten-metal hazards.
PPE must be selected by a workplace hazard assessment. Ordinary cotton clothing is not automatically sufficient primary protection against molten-metal splash; OSHA enforcement records document this point for foundry work. Clothing and footwear must not leave gaps through which molten metal can enter.
Critical warning: Never charge wet scrap, use damp tools, pour into a wet mold, or work near standing water. Moisture can flash to steam and eject molten metal. The UK Health and Safety Executive specifically warns that water contamination of molten metal can cause explosions; its molten-metals safety guidance recommends covered storage, drying where necessary, and visual inspection of scrap.
How to make cast aluminum bronze in 11 steps
1. Choose the alloy before choosing the recipe
Decide whether the required material is actually C95400. Do not use “bronze” as a recipe name. If the part requires a different aluminum bronze or a tin, silicon, or nickel bronze, its charge and process may need to change.
For sand castings, ASTM B148 is the relevant standard family for aluminum-bronze sand castings and includes C95400 among standardized copper-base casting alloys. The ASTM page currently displays ASTM B148-97(2009), with a historical last-update date of May 5, 2014. Do not describe that displayed edition as the newest ASTM edition without checking ASTM’s current subscription database.
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2. Calculate and weigh a nominal charge
For a nominal 1,000-gram charge using the simplified 85/11/4 target, the arithmetic is:
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| Material or element | Nominal mass |
|---|---|
| Copper | 850 g |
| Aluminum | 110 g |
| Iron | 40 g |
This is a starting calculation, not a guaranteed final analysis. A real foundry charge must account for the composition of each certified input, expected recovery, melting loss, dross, returns, and any required chemistry correction. Keep charge materials clean, dry, and traceable.
Separate crucibles, ladles, skimming tools, and charge storage for incompatible metals where practical. Residual lead, zinc, tin, or another bronze alloy can move the result outside the C95400 limits and change casting behavior. Mixed secondary copper-alloy scrap is a recognized source of uncontrolled composition.
3. Use a furnace and crucible rated for copper alloys
Confirm the furnace can reach and safely hold the required copper-alloy temperature without damaging its lining or controls. Confirm that the crucible is approved for the metal and treatment materials being used.
Inspect the crucible for cracks, erosion, chemical attack, and other damage. Inspect lifting tongs, ladles, skimmers, thermocouple protection tubes, and pouring equipment before heating. Preheat equipment according to the manufacturer’s procedure; preheating is not permission to use equipment that is damp, damaged, or not rated for the application.
4. Prepare a mold designed for shrinkage and feeding
C95400 has high solidification shrinkage, high drossing, medium fluidity, and medium gassing. The CDA data lists a patternmaker’s shrinkage allowance of 3/16 inch per foot. The mold therefore needs suitable allowances for shrinkage and machining, plus a gating and feeding system designed for the casting’s geometry.
Plan the sprue, pouring basin, runners, gates, risers, vents, cores, and parting line together. The goal is controlled filling and directional solidification: metal should reach the last-freezing regions from an effective feeder rather than leaving an isolated shrinkage cavity.
Gates should fill the cavity with as little turbulence as practical. Turbulence can fold the aluminum-rich surface oxide into the liquid, producing oxide-film defects that act like internal cracks and may contribute to porosity. For complex, expensive, or pressure-containing parts, casting simulation is preferable to guessing. The Inoxyda aluminum-bronze engineering guide describes how flow and solidification modeling can help identify misruns, oxide formation, mold erosion, and feeding problems before production.
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5. Dry the mold, charge, tools, and ladle
Everything that could contact molten metal must be dry, including:
- Scrap, ingot, and master alloy
- Crucible, ladle, tongs, and skimming tools
- Thermocouple probes and immersion equipment
- Molds, cores, sleeves, and refractory coatings
- Fluxes, covers, degassing equipment, and containers
Surface appearance is not enough. Porous refractory, corrosion pits, enclosed spaces, and closed containers can retain water. Store scrap under cover and dry it using a documented procedure. Reject sealed, hollow, oily, painted, or unknown items unless they have been safely processed for melting.
6. Charge copper and iron first
Charge known, clean copper and the iron-bearing addition before aluminum. Copper establishes the liquid bath, and iron can dissolve while the bath is at copper-alloy melting temperature rather than being added to a surface dominated by aluminum oxide.
Do not use galvanized steel, painted metal, sealed containers, oily scrap, or unknown hardware as charge material. Unidentified scrap may contain lead, zinc, cadmium, beryllium, or other elements that create hazardous fumes and uncontrolled chemistry. Keep the furnace covered or otherwise managed to limit unnecessary oxidation, and avoid excessive holding time and overheating.
Hydrogen pickup is affected by melt temperature and time. Industrial process documentation notes that melting temperature and duration are minimized to control hydrogen, whose solubility increases as temperature rises. Melt only what the mold and process require, and prepare the mold and pouring team before the metal is ready.
7. Add aluminum only after the copper bath is ready
Add aluminum in controlled pieces or, preferably, use a certified copper-aluminum master alloy. Feed additions with preheated equipment and, where the approved procedure permits, place them below the surface rather than dropping large cold pieces onto the bath.
Aluminum rapidly forms a stable oxide film. Mixing must be sufficient to homogenize the charge, but aggressive stirring can break that film into the melt and fold it into the metal. Research on hydrogen porosity and oxide-film defects explains why a melt can look uniform while containing harmful folded oxide films.
The common advice to “throw aluminum into molten copper and stir hard” is therefore unsafe and metallurgically incomplete. Follow the approved alloy supplier or foundry procedure for addition sequence and mixing.
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8. Measure temperature with a calibrated instrument
Use a calibrated thermocouple or immersion pyrometer suitable for copper alloys. Do not rely on “cherry red” color: perceived color changes with lighting, emissivity, oxide, furnace atmosphere, and operator perception.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallThe C95400 solidus and liquidus—approximately 1,027°C and 1,038°C—describe phase changes, not a universal pouring temperature. Required superheat depends on mold material, mold temperature, wall thickness, gating design, transfer distance, and filling time.
For context only, the Inoxyda guide gives 1,150–1,200°C as a normal casting range for nickel aluminum bronzes. That figure is not a universal specification for C95400 and should not simply be copied into a C95400 procedure. Establish the process window through the alloy supplier, governing specification, foundry trials, and qualified technical review.
9. Remove dross and use treatment only when specified
C95400 is rated as having high drossing and medium gassing, so dross control is essential. Skim with a dry, preheated tool, lifting the oxide layer away without plunging it back into the melt. Avoid unnecessary stirring immediately before pouring.
Do not treat borax as a universal aluminum-bronze flux or degasser. Fluxes, cover materials, deoxidizers, and degassing practices are alloy- and process-specific. Industrial references describe alloy-specific cover fluxes, fluoride-based fluxes, and inert-gas degassing rather than one household additive that works for every bronze.
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If degassing is required, use a commercial product exactly as specified in its technical data sheet, including drying, application, ventilation, and disposal requirements. Incorrectly dried or applied treatment materials can introduce moisture, inclusions, or hazardous fumes. The EPA technical material on copper-alloy melting provides useful context on treatment and hydrogen-control practices.
10. Pour steadily and minimize turbulence
Before lifting the crucible, verify that:
- The mold is closed, secured, vented, and completely dry.
- The pouring path and receiving area are clear and dry.
- The ladle and tools are preheated, inspected, and correctly positioned.
- Each person knows their position, task, and escape route.
- No one is holding the mold by hand or standing in an unnecessary exposure zone.
Pour in one controlled, continuous stream. Do not stop and restart unless the process specifically requires it. Do not scrape floating dross into the sprue. Where the mold design calls for it, maintain a full sprue or pouring basin without overflowing the mold or creating an uncontrolled stream.
Temperature and filling speed involve competing risks. Metal that is too cold, a cold mold, inadequate gates, or slow filling can produce misruns and cold shuts. Excessive temperature or prolonged holding can increase oxidation, hydrogen pickup, mold attack, and dross. Improve the complete process rather than solving every defect by overheating the melt.
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11. Cool, shake out, inspect, and finish
Allow the casting to solidify before shakeout. There is no transferable universal waiting time: safe shakeout depends on section thickness, mold material, casting mass, riser size, and the casting’s thermal behavior.
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- Cut off sprues, runners, and risers.
- Grind or machine gates and other excess metal.
- Inspect for misruns, cold shuts, cracks, inclusions, and shrinkage.
- Section a test coupon when internal soundness matters.
- Use qualified radiography, ultrasonic testing, dye penetrant, or another appropriate method for safety-critical work.
A good-looking surface does not prove that the interior is sound. Oxide films, slag inclusions, hydrogen porosity, and shrinkage cavities may be hidden until machining or sectioning. The Inoxyda guide identifies these defects as capable of affecting service performance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Optional C95400 heat treatment
C95400 is heat-treatable, but adding heat treatment to a hobby procedure without a controlled furnace, quench system, distortion plan, and acceptance criteria can create more problems than it solves.
CDA data lists the following reference treatments:
| Treatment | Reference temperature |
|---|---|
| Solution treatment | 1,600–1,675°F (871–913°C), followed by water |
| Annealing | 1,150–1,225°F (621–663°C) |
| Stress relief | Approximately 600°F (316°C) |
These temperatures do not by themselves define a complete heat-treatment recipe. Time, section-thickness allowances, furnace uniformity, quench practice, distortion control, and required mechanical properties must come from the governing material specification or a qualified metallurgist.
Troubleshooting cast aluminum bronze
| Observed problem | Likely causes | Corrective direction |
|---|---|---|
| Violent eruption or splash | Water in scrap, mold, tool, ladle, or refractory | Stop the operation and isolate the area. Review drying, covered storage, inspection, and emergency procedures before restarting. |
| Misrun or cold shut | Metal or mold too cold, inadequate gating, or slow filling | Improve measured temperature control, mold/process design, and filling speed; do not simply overheat the melt. |
| Black or flaky internal defects | Folded aluminum-oxide films caused by turbulent mixing or pouring | Reduce turbulence, avoid violent stirring, and improve transfer and gating. |
| Rounded internal pores | Hydrogen pickup and precipitation during solidification | Keep materials dry, minimize holding time, use qualified degassing, and verify by sectioning or testing. |
| Shrinkage cavity | Inadequate riser, poor directional solidification, or insufficient feed metal | Redesign risers and the solidification path; C95400 has high solidification shrinkage. |
| Brittle or inconsistent properties | Wrong alloy, uncontrolled iron or nickel, oxidation, or unsuitable cooling or heat treatment | Use certified charge materials and chemical analysis rather than appearance-based identification. |
| Heavy dross loss | Dirty charge, excessive superheat, long holding time, or aggressive oxidation | Use clean charge, minimize holding, skim correctly, and use only validated treatment materials. |
| Burns through clothing or footwear | PPE gaps or equipment not selected for molten-metal splash | Reassess the hazard controls and PPE with a competent safety professional. |
Common online advice that needs correction
- “Bronze melts at one standard temperature.” Incorrect. Bronze grades differ, and solidus/liquidus temperatures are not the same as a process-specific pouring temperature.
- “Color tells you when the melt is ready.” Color is not a calibrated temperature measurement.
- “Borax degasses aluminum bronze.” Do not generalize this claim. Fluxing and degassing depend on alloy and process.
- “Any clean-looking copper and aluminum makes C95400.” C95400 has controlled aluminum and iron ranges and limits for nickel, manganese, and other elements.
- “A cold, dry mold is always best.” Mold temperature is part of the filling and solidification design and depends on the mold system, casting geometry, and alloy.
- “The casting is sound if the outside looks good.” Internal oxide films, porosity, and shrinkage require sectioning or qualified nondestructive testing when soundness matters.
- “Cotton clothing is sufficient molten-metal PPE.” Ordinary cotton is not automatically adequate primary protection against direct molten-metal splash.
Frequently Asked Questions
Can a beginner make aluminum bronze at home?
It is not a suitable beginner project. C95400 requires temperatures above 1,000°C (1,830°F), copper-alloy-rated equipment, dry molds and tools, controlled ventilation, molten-metal PPE, and procedures for preventing explosive steam releases. A trained foundry is the safer option.
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What is the recipe for C95400 aluminum bronze?
The nominal composition is about 85% copper, 11% aluminum, and 4% iron. The specification limits are broader and also control nickel and manganese. Weighing those nominal masses does not guarantee the final chemistry; certified charge materials and chemical analysis are needed for specification work.
What temperature do you pour aluminum bronze?
There is no single universal pouring temperature. C95400’s approximate solidus and liquidus are 1,027°C and 1,038°C, but the required superheat depends on the mold, section thickness, gating, transfer distance, and filling time. Use a calibrated instrument and an approved process window.
Can I use borax as a flux for aluminum bronze?
Do not treat borax as a universal flux or degasser for aluminum bronze. Use only alloy-compatible commercial treatment materials and follow their technical data sheets and the foundry’s validated procedure.
How do I know whether an aluminum-bronze casting is sound?
Visual inspection alone is insufficient. Sectioning, a test coupon, radiography, ultrasonic testing, dye penetrant inspection, or another qualified method may be needed, especially for safety-critical or pressure-containing parts.
The Bottom Line
Bottom line: Making cast aluminum bronze successfully is less about finding a simple melting recipe and more about controlling alloy chemistry, moisture, oxidation, turbulence, shrinkage, temperature, and inspection. C95400 is a useful reference alloy, but a reliable casting process should be developed and run by trained foundry personnel with certified materials and documented controls.
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