This article will delve into the melting point of bronze. As an alloy, bronze’s melting point is not a precise numerical value as one might imagine. Gaining a deeper understanding of the factors influencing bronze’s melting point and its critical role in industrial manufacturing will help you optimise processes in casting, welding, and other techniques, thereby reducing product defects. Both metal processing plants and casting purchasers stand to benefit from this knowledge.
What is the Melting Point of Bronze
The melting point range of bronze is between 850°C and 1050°C, or 1562°F and 1832°F. This means the melting process of bronze occurs gradually within this temperature range. Unlike pure metals, which have a precise melting point—such as copper at 1085°C (1984°F)—alloys exhibit a broader melting range.
Melting Process of Bronze
The melting of bronze is quite fascinating because it does not transition instantly from solid to liquid. As the metal heats, it absorbs heat, intensifying atomic motion. The temperature gradually rises to the solidus line—the lowest temperature at which melting begins. At this point, the metal begins to transform from solid to liquid. The temperature ceases to rise, and the absorbed heat is used to disrupt the internal crystal structure until the temperature reaches the liquidus line—the point at which the alloy becomes fully liquid. Throughout the entire melting process, solid and liquid phases coexist within the metal. This transitional region is known as the mushy zone.
Melting Point vs. Pouring Temperature in Casting
If you think that heating bronze to its melting point is sufficient for casting, you couldn’t be more wrong. In foundries, the pouring temperature of metal is typically set 100-150°C above its liquidus line. This ensures the molten metal possesses sufficient fluidity to fill the mold cavity before solidification—particularly crucial for complex cavities in investment casting. Failure to achieve this may result in investment casting defects such as cold shuts or insufficient filling.
Melting Point of Bronze Family
Bronze alloys form a large family encompassing multiple similar yet distinct alloy types. The table below summarises the melting point ranges of common bronze alloys.
| Alloy Type | Main Composition | Melting Range | Casting Characteristics |
| Tin Bronze | Cu, Sn (2%~20%) | 900°C – 1050°C | Excellent fluidity with minimal shrinkage, resulting in negligible casting shrinkage. Suitable for precision components, gears, and artistic castings. |
| Aluminum Bronze | Cu, Al (5%~12%), Fe, Ni | 1027°C – 1045°C | High melting point, exceptional strength, and excellent wear and corrosion resistance. Commonly used for marine propellers and pump/valve castings. |
| Silicon Bronze | Cu, Si (1%~5%) | 980°C – 1025°C | Highly weldable with strong corrosion resistance. One of the most commonly used alloys in investment casting. |
| Phosphor Bronze | Cu, Sn, P (0.1%~0.5%) | 900°C – 1020°C | Phosphorus enhances melt fluidity and aids in deoxidation. Frequently used for casting springs, electrical contacts, and wear-resistant bearings. |
| Leaded Tin Bronze | Cu, Sn, Pb (25% max) | 850°C – 1000°C | Low melting point with excellent self-lubricating properties and machinability. Primarily used in manufacturing high-speed bearing shells. |
| Manganese Bronze | Cu, Zn, Mn, Al, Fe | 865°C – 890°C | Essentially a high-strength brass. Features a low melting point yet extremely high strength, commonly employed in producing heavy-duty mechanical components. |
Effect of Alloying Elements on the Melting Point of Bronze
After reviewing the table above, you may wonder why bronze alloys exhibit such significant differences in melting points despite sharing the same base material. This relates to the topic we’ll discuss next—alloying elements. These elements interact with copper, influencing the alloy’s solidus and liquidus lines.
Below, I will list the primary alloying elements and their effects on the melting point range of bronze alloys.
| Element | Effect on Melting Behaviour | Metallurgical Notes |
| Sn | Significantly reduce the melting point | This will cause the molten pool to expand during the metal melting process, making it prone to shrinkage defects. |
| Pb | Solidus line steeply decreases | At 327°C, a liquid phase appears, which can improve the material’s machinability. |
| Al | When the aluminium content is <10%, the melting point of the metal increases. When the aluminium content is >12%, the melting point may decrease. | It can enhance the oxidation resistance of materials, but it is highly prone to producing oxidation slag inclusions during casting. |
| Ni | Slightly increases the melting point range (~10–20 °C). | It can enhance the high-temperature strength and creep resistance of materials. |
| Zn | slightly lower its melting point | It can improve the fluidity of metal during casting. Excessive zinc content requires consideration of the risk of metal volatilisation. |
| P | Slightly increase the solidus temperature | Commonly used as a fluxing agent and deoxidizer in casting. |
What Can Affect the Melting Point of Metals?
The melting point of metals is determined by multiple factors, including primary factors—chemical composition and atomic structure—and secondary factors—impurities.
Alloy Composition
The melting point of a metal is fundamentally governed by its chemical composition. As mentioned earlier, pure metals possess a single, fixed melting point. However, when other alloying elements are added to form bronze, its melting point ceases to be a precise numerical value and instead becomes a melting temperature range.
Atomic Structure
From a microscopic perspective, the melting process of metals involves thermal energy overcoming the interatomic bonding forces (i.e., metallic bonds) between atoms, thereby disrupting the long-range ordered structure of the crystal lattice. The melting point of a metal primarily depends on the interatomic bonding energy, which is related to its crystal structure (FCC or BCC). Atomic structures with higher bonding energies require greater heat absorption to transition the metal from a solid to a liquid state, resulting in a higher melting point
Impurities
The impurity content in metals also affects their melting point, potentially causing a melting point depression effect. Certain impurities (such as sulfur and phosphorus) may segregate at grain boundaries and form low-melting-point eutectic phases, leading to localised melting of the metal below the expected temperature.
Applications of Melting Point in Production
Once we gain a thorough understanding of bronze’s melting point, we can perform precise operations based on this property across various production environments, such as setting process parameters. Operating without regard to the melting point’s characteristics may directly result in product scrapping.
Investment Casting
In investment casting, the melting point of the metal serves as the sole reference for setting the pouring temperature. The pouring temperature must exceed the alloy’s liquidus line (i.e., possess a certain degree of “superheat”) to ensure the fluidity of the molten metal.
If the pouring temperature is too low (approaching or even falling below the alloy’s melting point), the molten metal may solidify before filling the ceramic mould shell, resulting in cold shuts or insufficient filling.
If the pouring temperature is too high (significantly exceeding the metal’s melting point), the high-temperature molten metal will absorb large amounts of hydrogen and oxygen from the air during pouring. As the casting cools and solidifies, this leads to severe internal porosity. High temperatures may even cause the casting to undergo rapid volumetric shrinkage, resulting in extensive shrinkage cavities and triggering severe mould shell reactions.
Welding
When joining bronze components or repairing casting defects, it is essential to clearly understand the relationship between the melting points of the base metal and the filler material.
If the temperature during welding is insufficient and fails to reach the melting point of either the filler material or the base metal, incomplete fusion or cold joints may occur. This means the filler material merely adheres to the surface of the base metal without achieving a metallurgical bond, causing the weld to fracture under even slight stress.
Conversely, excessive heat input during welding—even exceeding the base metal’s melting point—can cause burn-through or collapse deformation of the base metal. In conventional fusion welding, excessive heat input may result in coarse-grained structure within the heat-affected zone (HAZ), leading to embrittlement of the joint.
Heat Treatment
Bronze castings typically require annealing or solution treatment to enhance their mechanical properties. However, many are unaware that heat treatment must be conducted while the metal remains in its solid state, and the temperature must never reach or exceed the metal’s solidus line.
If the heat treatment temperature is too low, the atoms lack sufficient kinetic energy for diffusion. Consequently, the internal microstructure of the metal cannot be improved, and internal stresses cannot be released. In such cases, the heat treatment becomes ineffective and fails to enhance the casting’s properties.
Conversely, excessively high temperatures may inflict catastrophic overheating defects. At elevated temperatures, low-melting-point intergranular substances melt and oxidise first, causing irreversible damage to the metal’s mechanical properties and rendering it as brittle as a cookie. The only remedy is to remelt the part.
How to Determine the Melting Point of Bronze
If you wish to determine the melting range of bronze yourself, it can be measured using the following laboratory methods.
Differential Scanning Calorimetry
Differential Scanning Calorimetry (DSC) identifies the melting point by comparing the heat flow differences between a sample and a reference material during simultaneous heating, thereby detecting the endothermic peak generated during the sample’s melting process. This method offers high precision (typically ±0.1–1°C) and can analyse samples as small as milligrams.
Optical Pyrometer
Optical pyrometers utilize blackbody radiation theory and brightness comparison to non-invasively measure the radiant brightness of high-temperature objects. By comparing this brightness to that of a known-temperature light source, they determine surface temperature. Thus, observing changes in metal during heating allows indirect determination of its melting point.
Thermal Analysis Techniques
Phase transformation behavior is assessed by recording the temperature-time curve of a metal during cooling. For pure metals, a plateau appears at the onset of solidification; this plateau temperature represents the melting point. For alloys, phase transitions manifest as a slowing cooling rate or an inflection point on the curve, corresponding to the liquidus or solidus temperatures.
Preventing the Primary Melting Defects
If process parameters are set arbitrarily without reference to the metal’s melting point during casting, it may lead to various casting defects, including porosity. Below are four primary defects related to the melting point range and their preventive measures.
Segregation and Microstructural Inhomogeneity
Cause: Wide solidification range (e.g., high-tin bronze) causes low-melting-point elements to enrich in the last-solidifying zone during cooling.
Impact: Reduced product toughness and susceptibility to intergranular corrosion.
Prevention: Control cooling rate, optimize material composition, and perform uniform heat treatment.
Gas Porosity and Shrinkage Cavities
Cause: Excessively high pouring temperature enhances the gas-dissolving capacity of molten metal.
Impact: Multiple gas pores form within the casting, compromising its strength.
Prevention: Refine and degas the metal, reduce pouring temperature (not exceeding recommended superheat).
Hot Tearing / Solidification Cracking
Cause: Casting shrinkage is impeded during the solid-liquid coexistence phase.
Impact: Compromises the structural integrity of the casting.
Prevention: Optimize mold design and control cooling rates.
Overheating and Loss of Alloying Elements
Reason: Excessively high pouring temperature increases the volatilization and oxidation of elements (particularly low-melting-point elements like zinc and tin).
Impact: Reduced material strength and increased brittleness.
Prevention: Control overheating; vacuum melting may be employed.
Melting Point of Bronze vs Other Metals
After learning about the melting point of bronze, you may be curious about the melting points of other metals. The table below provides the melting points or melting ranges for several common metals.
| Metal | Melting Point (°C) | Melting Point (°F) |
| Tin (Sn) | 232°C | 450°F |
| Lead (Pb) | 327°C | 621°F |
| Zinc (Zn) | 419°C | 787°F |
| Aluminium (Al) | 660°C | 1,221°F |
| Brass (Alloy) | ~900–940°C | ~1,650–1,725°F |
| Silver (Ag) | 961°C | 1,763°F |
| Gold (Au) | 1,064°C | 1,948°F |
| Copper (Cu) | 1085°C | 1984°F |
| Cast Iron (Alloy) | ~1,150–1,200°C | ~2,100–2,200°F |
| Carbon Steel (Alloy) | ~1370-1510℃ | ~2498-2750℉ |
| Stainless Steel (Alloy) | ~1400–1530°C | ~2550–2800°F |
| Iron (Fe) | 1538℃ | 2800℉ |
| Titanium (Ti) | 1,668°C | 3,034°F |
| Tungsten (W) | 3,422°C | 6,192°F |
| Nickel (Ni) | 1,453°C | 2,647°F |
Conclusion
That’s all I wanted to share about melting points. I trust you’ve gained valuable insights into the melting points of metals. If you’re considering investment casting for your bronze casting project, Pingheng Machinery is your ideal choice. We cast a wide range of bronze alloys, including tin bronze, aluminum bronze, phosphor bronze, and silicon bronze. We also offer machining services, providing a one-stop solution for all your needs. Should you have any questions regarding casting, feel free to contact us for consultation.
FAQ
Q1. Which metal melts most easily?
Among common industrial casting metals, lead has an exceptionally low melting point of only 232°C, making it one of the easiest metals to melt. Additionally, tin and zinc also have melting points significantly lower than bronze, offering superior workability.
Q2. Can bronze be recycled after melting?
Certainly. Bronze holds significant recycling value. Although some volatile elements (zinc, lead) may be lost during repeated melting, professional foundries ensure that recycled bronze castings fully comply with ASTM or EN standards.
Q3. Is the pouring temperature of bronze the same as its melting point?
This is a common misconception. To ensure sufficient fluidity in liquid metal, the pouring temperature of the metal (bronze) is typically set approximately 100°C to 150°C higher than its liquidus line (the temperature at which it is fully molten).
Q4. Does adding more tin always lower bronze’s melting point?
When the tin content is within 15%, the liquidus temperature of the alloy decreases as the tin content increases. However, beyond this range, the alloy’s liquidus temperature slightly increases.
Q5. Is lead always beneficial for lowering bronze’s melting point?
Although lead lowers the melting point of metals and significantly improves the machinability of castings, when its content exceeds 5%, it causes the metal to become brittle at high temperatures. This introduces the risk of hot cracking during casting and renders the material unsuitable for high-temperature applications.
Q6. Can all bronze be brazed by heating to its melting point?
No, when brazing bronze, you must select filler material with a lower melting point to join the parts. Otherwise, it may cause the wood to melt, resulting in fusion defects.
Q7. What is the melting point range for bronze used in marine propellers?
Marine propeller materials are typically C92200 naval tin bronze (containing 10% Sn) or C61400 medium aluminium bronze (containing 10% Al). The former has a melting point range of 920–1020°C, while the latter ranges from 1050–1130°C. Aluminium bronze is preferred for large propellers due to its superior strength at elevated temperatures.
Q8. Why does aluminium bronze have a higher melting point range than tin bronze?
Aluminium bronze contains not only aluminium but also high-melting-point elements such as iron and nickel. These elements combine with copper to form dense, high-temperature-resistant intermetallic compounds, thereby increasing the melting point of aluminium bronze. In contrast, the addition of tin disrupts the atomic bonding and lowers the metal’s melting point range.
Q9. Why is the melting point important in metal applications?
The melting point of a metal directly determines the casting processes that can be used and its end-use applications. Understanding a metal’s melting point helps prevent casting defects and premature failure of castings during production and use.
Q10. Does the melting point of bronze change with repeated casting?
Minor changes will occur. Repeated casting causes low-melting-point or volatile alloying elements in bronze to be burned off. Alterations in the composition ratio naturally lead to shifts in the alloy’s melting point and physical properties.
Q11. How does overheating bronze during melting affect the casting quality?
Overheating is a major no-no in casting. It can cause the molten metal to absorb excessive amounts of gas, resulting in numerous gas pores within the solidified casting. Overheated molten metal may also cause elements to volatilize or react chemically with the ceramic shell mould used in investment casting, leading to a rough casting surface.
Q12. What is the typical shrinkage rate of bronze after it cools from its melting point?
The typical linear shrinkage rate for bronze generally ranges between 1.5% and 2.0%. The shrinkage rate for aluminium bronze is typically greater than that for tin bronze. Engineers must calculate shrinkage allowances during the mould design phase to account for casting shrinkage.
Q13. Why do investment foundries need different shell materials for different bronze alloys?
Different types of bronze (such as high-melting-point aluminium bronze and lower-melting-point tin bronze) can exhibit casting temperature differences exceeding 150°C. Consequently, alloys requiring higher casting temperatures necessitate more stable ceramic materials with superior refractory properties.
