Brass melting temperatures vary by over 100°C between common commercial grades — and the variation is not random. It follows a precise, predictable relationship governed by the copper-zinc binary phase diagram. Understanding why gives you a tool for predicting melting behavior from composition data alone, which matters for casting, brazing, laser cutting parameter selection, and any process where thermal management of the material is critical.
The short answer: every percentage point of zinc added to copper lowers the brass melting temperature (solidus) by approximately 1.2–1.5°C. Moving from red brass (C23000, 15% Zn, solidus ~990°C) to Muntz metal (C28000, 40% Zn, solidus ~885°C) lowers the solidus by 105°C. That 105°C variation is predictable, calculable, and physically understood.
The longer answer involves the Cu-Zn phase diagram, the liquidus-solidus gap (the “mushy zone”), and the additional effects of lead, tin, and other alloying elements on top of the base zinc effect. This article covers all three.
The Root Cause: Zinc Depresses the Brass Melting Temperature
When zinc dissolves into copper, it does not simply mix — it changes the thermodynamic conditions under which the solid and liquid phases coexist. The Cu-Zn binary phase diagram quantifies this relationship.
The Cu-Zn phase diagram — key features
The copper-zinc equilibrium phase diagram plots the phase boundaries (liquidus and solidus) as a function of temperature and zinc composition. The critical features for understanding brass melting temperature:
The liquidus line descends from pure copper’s melting point (1,085°C) nearly continuously as zinc content increases. Each added percentage of zinc lowers the liquidus by approximately 7–9°C per percent zinc — a slope comparable to what carbon does to steel.
The solidus line descends more steeply than the liquidus at low zinc contents, creating a widening gap (mushy zone) as zinc increases. The solidus then flattens slightly in the alpha-beta two-phase region (above approximately 37% Zn at room temperature).
The alpha-beta boundary at approximately 37% Zn (room temperature) represents a crystal structure change: below this composition, brass is all alpha (FCC, single-phase). Above it, beta phase (BCC) appears alongside alpha. This boundary shifts with temperature. At elevated temperatures, the beta field expands toward lower zinc contents — meaning Muntz metal (40% Zn) and free-cutting brass (35.5% Zn + 3% Pb) are partly in the alpha-beta region during solidification even if they are nominally single-phase at room temperature.
The linear approximation for fabricators
For practical use without reference to the full phase diagram, the linear approximation holds adequately across the commercial brass range (10–40% Zn):
Solidus temperature ≈ 1,085°C − (1.3 × %Zn)
Applied to common grades:
- C23000 (15% Zn): 1,085 − (1.3 × 15) = 1,085 − 19.5 = 1,065.5°C (actual: ~990°C — less accurate at low Zn due to the non-linear early segment; use the alloy-specific data for precision)
- C26000 (30% Zn): 1,085 − (1.3 × 30) = 1,085 − 39 = 1,046°C (actual liquidus ~955°C; the approximation gives a relative comparison, not absolute accuracy)
- C28000 (40% Zn): 1,085 − (1.3 × 40) = 1,085 − 52 = 1,033°C (actual liquidus ~905°C)
The linear approximation overestimates the absolute temperature — the actual liquidus descent is steeper than a simple linear rule because of the way zinc interacts with the FCC copper lattice at the quantum level. But the relative effect holds: more zinc = lower melting temperature, consistently and predictably.
How the Mushy Zone Width Changes With Composition
The inconsistency in brass melting temperature is not just about a single solidus value — it is about the width of the two-phase (liquid + solid) region, which changes dramatically with composition.
Why the mushy zone matters
When a brass alloy cools from fully liquid, it enters the mushy zone at the liquidus temperature. Solidification is not instantaneous — it proceeds through a range as the composition of the remaining liquid shifts (becoming more zinc-rich, since the solid that forms is copper-richer than the alloy average). The alloy is not fully solid until the solidus is reached.
The mushy zone width (liquidus − solidus) determines:
- Feeding difficulty in casting: Wide mushy zone = more solidification shrinkage to feed, greater risk of centerline porosity
- Segregation severity: Wide mushy zone = more time for composition gradients to develop between early- and late-solidifying regions
- Brazing thermal margin: Wide mushy zone = the temperature range over which the filler is partially solidified must stay above the liquidus, not just above the average
Mushy zone width by grade
| Brass grade | Zinc % | Solidus (°C) | Liquidus (°C) | Mushy zone (°C) |
|---|---|---|---|---|
| C22000 (commercial bronze) | 10 | 1,010 | 1,045 | 35 |
| C23000 (red brass) | 15 | 990 | 1,025 | 35 |
| C24000 (low brass) | 20 | 975 | 1,000 | 25 |
| C26000 (cartridge brass) | 30 | 915 | 955 | 40 |
| C27000 (yellow brass) | 35 | 905 | 932 | 27 |
| C28000 (Muntz metal) | 40 | 885 | 905 | 20 |
| C36000 (free-cutting) | 35.5 + 3% Pb | 885 | 900 | 15 |
Source: ASM Handbook, Volume 2; ASM Binary Alloy Phase Diagrams.
The mushy zone width is not monotonically related to zinc content. It increases going from C22000 to C26000 (the 40°C maximum), then narrows again toward C28000 and C36000. This non-monotonic behavior reflects the location of the alloy composition relative to the peritectic and alpha-beta phase boundary features of the Cu-Zn diagram.
The narrow mushy zone of C36000 (15°C) is one reason free-cutting brass is excellent for casting: narrow solidification range means less time in the partially solidified state, less microsegregation, and easier riser feeding.
How Lead Affects Brass Melting Temperature
Free-cutting brass (C36000) contains approximately 3% lead, which changes the melting behavior in a way distinct from zinc’s effect.
Lead’s limited solubility in brass
Unlike zinc, which dissolves completely in the copper-zinc lattice up to the alpha-beta boundary, lead has extremely limited solubility in solid brass — approximately 0.03% at room temperature. Lead forms a separate liquid phase at the grain boundaries during solidification.
This means that when a C36000 melt cools, the following sequence occurs:
- At ~900°C (liquidus of the brass matrix): copper-zinc solid begins forming
- Lead remains in the liquid phase, concentrating progressively as the brass solidifies
- At ~887°C: the remaining lead-rich liquid resolidifies as lead droplets at the grain boundaries
- The brass matrix solidus is reached at ~885°C
The lead effect on the nominal solidus and liquidus temperatures of the brass matrix is small (approximately 2–5°C depression from the eutectic behavior of the Cu-Pb-Zn system). The more significant effect is the lead melting point (327°C): because lead exists as a separate phase with its own melting point, any heat treatment above 327°C risks re-melting the lead phase, leading to liquid metal embrittlement under stress.
For fabricators: Free-cutting brass with lead additions cannot be hot-worked above approximately 500°C (well above lead’s melting point but below the temperature at which liquid lead causes cracking). Laser cutting C36000 produces a HAZ where the temperature briefly exceeds 327°C, but the extremely rapid heating and cooling cycle limits the time the lead phase spends molten. The risk of lead embrittlement from laser cutting HAZ is low for thin sections but should be evaluated for thick-section structural applications.
How Tin, Aluminum, and Silicon Further Modify Brass Melting Temperature
Commercial brass alloys beyond the simple Cu-Zn system include additional alloying elements, each with their own effect on the brass melting temperature:
Tin — Naval brass and admiralty brass
Naval brass (C46400) contains 0.75% tin alongside its 39.25% zinc. Tin dissolved in the brass matrix raises the liquidus slightly compared to a binary Cu-Zn alloy at the same zinc content:
| Grade | Zn % | Sn % | Liquidus (°C) | Solidus (°C) |
|---|---|---|---|---|
| C28000 (Muntz metal) | 40 | 0 | 905 | 885 |
| C46400 (naval brass) | 39.25 | 0.75 | 935 | 900 |
The ~30°C liquidus increase from 0.75% tin reflects tin’s higher melting point (232°C — lower than copper but much higher than zinc), which modifies the liquidus line of the ternary Cu-Zn-Sn system in the direction that raises the melting temperature compared to a zinc-equivalent binary brass.
Aluminum — Aluminum brass
C68700 (aluminum brass, 76% Cu, 22% Zn, 2% Al) has a liquidus of approximately 1,010°C — significantly higher than a binary C27000 brass (35% Zn, liquidus 932°C) despite the high zinc content. Aluminum (melting point 660°C) raises the liquidus through its interaction with both copper and zinc in the ternary Cu-Zn-Al phase system. Aluminum also dramatically reduces dezincification susceptibility — which is the commercial reason for its addition, not the thermal modification.
Silicon — Silicon brass and silicon bronze
C87300 (silicon bronze/brass, ~Cu-1%Si) has a liquidus of approximately 1,060°C — close to pure copper despite alloying. Silicon raises the melting temperature of copper alloys, which is why silicon bronzes are preferred for high-temperature brazing applications where zinc-bearing brass fillers would lose zinc through volatilization.
What the Melting Temperature Variation Means for Laser Cutting Brass
For fiber laser cutting of brass, the melting temperature variation across grades has three practical consequences:
1. Power requirements by grade: A laser cutting machine making a clean cut through C23000 red brass (liquidus ~1,025°C) requires more energy per unit volume to maintain the melt front than cutting C36000 free-cutting brass (liquidus ~900°C) — because the melt front temperature must reach the liquidus to achieve complete material removal. This is a secondary effect compared to reflectivity and thermal conductivity, but it is real.
2. Nitrogen assist gas pressure: High-pressure nitrogen is the standard assist gas for all brass grades requiring clean, dross-free edges. The melt viscosity at the liquidus temperature varies with composition — high-zinc brasses (C28000, C36000) at their lower liquidus temperatures have lower melt viscosity than red brass (C23000) at its higher liquidus, making the melt more responsive to gas blowing pressure. Lower assist gas pressure is typically sufficient for high-zinc brasses compared to low-zinc brasses at equivalent thickness.
3. HAZ microstructure: The mushy zone width determines how much of the material adjacent to the laser kerf passes through partial solidification on cooling. For narrow-mushy-zone alloys (C36000, 15°C range), the HAZ transitions sharply between fully molten and fully solid. For wide-mushy-zone alloys (C26000, 40°C range), a broader partially solidified zone forms adjacent to the kerf. This does not normally affect cut quality but can affect the microstructure of the cut edge and any subsequent brazing or soldering operations on the cut face.
The complete parameter guide for fiber laser cutting of brass, including reflectivity management and nitrogen pressure recommendations, is in our laser cutting brass guide. The role of nitrogen vs. oxygen assist gas across all brass grades is covered in our assist gas selection guide.
Frequently Asked Questions About Brass Melting Temperature
Q: What is the melting temperature of brass?
Brass melting temperature depends on the grade. For yellow brass (C27000, 35% Zn): solidus 905°C, liquidus 932°C. For cartridge brass (C26000, 30% Zn): 915–955°C. For red brass (C23000, 15% Zn): 990–1,025°C. For free-cutting brass (C36000): 885–900°C. The solidus (where melting begins) and liquidus (where melting is complete) bracket the mushy zone — the partially molten range during which both solid and liquid coexist.
Q: Why does brass melt at a lower temperature than copper?
Because zinc (melting point 419°C) depresses the copper melting point when dissolved in the lattice. Each percent of zinc lowers the solidus by approximately 1.2–1.5°C. At 40% zinc (Muntz metal), the solidus is approximately 885°C — 200°C below pure copper’s 1,085°C melting point. The mechanism is thermodynamic: dissolved zinc changes the Gibbs free energy landscape of the copper-zinc system, lowering the temperature at which the liquid phase becomes stable.
Q: Why do different brass grades have different melting temperatures?
Because they have different zinc contents. Every commercial brass grade has a different copper-to-zinc ratio, and each percentage point of zinc lowers the melting temperature. Red brass (15% Zn) melts at a much higher temperature than yellow brass (35% Zn) for this reason. Additional alloying elements (tin in naval brass, aluminum in aluminum brass, lead in free-cutting brass) further modify the melting temperature based on their own thermodynamic interactions with the Cu-Zn system.
Q: What is the melting temperature of C36000 free-cutting brass?
C36000 free-cutting brass (61.5% Cu / 35.5% Zn / 3% Pb) has a solidus of approximately 885°C and a liquidus of approximately 900°C — giving a very narrow 15°C mushy zone. This narrow solidification range, combined with the lead phase that improves machinability, makes C36000 one of the best-behaved alloys for casting. The lead adds a separate phase at the grain boundaries with its own melting point of 327°C, which must be considered when heat treating or welding C36000.
Q: Does the mushy zone affect how brass behaves during laser cutting?
Not directly — laser cutting operates at temperatures well above the entire solidus-to-liquidus range, and the difference in melt viscosity between grades is small compared to the effect of reflectivity and thermal conductivity. However, the mushy zone width does affect the microstructure of the solidified layer at the cut edge and the risk of microsegregation in any region that partially re-melts and re-solidifies adjacent to the kerf. Wide-mushy-zone brasses (C26000) show more pronounced compositional variation at the cut edge than narrow-mushy-zone brasses (C36000).
References
- ASM Handbook, Volume 2: Properties and Selection — Nonferrous Alloys and Special-Purpose Materials, 10th Edition. ASM International, Materials Park, OH, 1990. (Solidus and liquidus temperatures for C22000–C46400 brass alloys; Cu-Zn binary phase diagram features; alpha-beta phase boundary; effect of lead, tin, aluminum, and silicon on brass liquidus temperatures.)
- Massalski, T.B., ed., Binary Alloy Phase Diagrams, 2nd Edition. ASM International, Materials Park, OH, 1990. (Cu-Zn binary phase diagram with full liquidus and solidus lines; alpha-beta phase boundary as a function of temperature; peritectic reactions and their effect on the mushy zone shape for different zinc contents.)
- ASTM B36/B36M, Standard Specification for Brass Plate, Sheet, Strip, and Rolled Bar, ASTM International, current edition. (Composition limits for C22000–C28000 and C36000 brass grades: copper, zinc, and lead content ranges; UNS designations; the procurement specification that defines the alloy compositions whose melting temperatures are analyzed throughout this article.)
- Haynes, W.M., ed., CRC Handbook of Chemistry and Physics, 104th Edition. CRC Press, Boca Raton, FL, 2024. (Pure metal melting points: copper 1,085°C, zinc 419°C, lead 327°C, tin 232°C; thermodynamic basis for melting point depression in binary alloys; Clausius-Clapeyron and Raoult’s law context for the zinc depression calculation.)
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