Aliuminis, as a lightweight, atsparus korozijai, and highly malleable non-ferrous metal, plays an irreplaceable role in aerospace, Automobilių gamyba, Elektronika, ir statybos pramonei.
The melting point of aluminum—defined as the temperature at which aluminum transitions from a solid to a liquid state under standard atmospheric pressure—is a fundamental thermophysical property that governs its processing, lydinio dizainas, and industrial application.
1. Physical properties of pure aluminum — key melting-point data
| Nuosavybė | Vertė (IR) | Vertė (Imperatoriškasis) | Pastabos |
| Lydymosi temperatūra (equilibrium, 1 atm) | 660.32 ° C. (933.47 K) | 1220.58 ° F. | Standard reference temperature for pure (99.999%) Al. |
| Thermodynamic temperature | 933.47 K | - | Absolute temperature equivalent. |
| Latent heat of fusion | 397 kJ·kg⁻¹ | ≈ 170.68 BTU·lb⁻¹ | Energy required to melt 1 kg (arba 1 lb) at melting point. |
Specific heat (kietas, apytiksliai, near 25 ° C.) |
897 J·kg⁻¹·K⁻¹ | ≈ 0.2143 BTU·lb⁻¹·°F⁻¹ | Use temperature-dependent cp for precise heat calculations. |
| Tankis (kietas, ~20 °C) | 2,700 kg·m⁻³ | ≈ 168.6 lb·ft⁻³ | Liquid density is slightly lower and temperature dependent. |
| Boiling point (atmospheric) | ≈ 2,470 ° C. | ≈ 4,478 ° F. | Useful upper bound for high-temperature processing. |
2. Key Factors Influencing the Melting Point of Aluminum
Although pure aluminum melts at 660.32 ° C., many practical factors alter the effective melting/solidification behaviour:
Alloy chemistry — solidus and liquidus
Aluminum alloys do ne have a single melting point. They have a skystis (temperature above which fully liquid) ir a solidus (temperature below which fully solid).
Legiruojamųjų elementų buvimas (Ir, Mg, Cu, Zn, Fe, kt.) shifts these boundaries and often produces a melting range (mushy zone) with important casting consequences.
- Eutectics: some alloy systems have eutectic compositions that melt at temperatures žemiau that of pure Al (pavyzdys: Al–Si eutectic at ≈ 577 ° C. for ~12.6 wt% Si).
- Practical effect: alloys with a wide freezing range are more prone to hot tearing, shrinkage porosity and segregation.
Impurities and tramp elements
Trace contamination (Pvz., Pb, Bi, Cu from mixed scrap) can create low-melting phases or brittle intermetallics, cause local melting anomalies and change solidification paths; this is critical in recycling operations.
Spaudimas
Melting temperature is pressure-dependent (Clapeyron relation); industrially this effect is negligible since melting is performed at atmospheric pressure.
Grain refiners and inoculants
Chemical grain refiners do not change the melting point per se, but they influence nucleation behaviour during solidification (undercooling, number of nuclei), thus altering the practical solidification pathway and microstructure.
Surface phenomena and oxide films
Aluminum forms a stable alumina film (Al₂O3) ant paviršiaus. While the oxide does not change bulk melt temperature, it affects heat transfer at the surface, dross behaviour and the thermal arrest behaviour detected by contact/pyrometric methods.
3. Melting ranges of common aluminum alloys
Below are two concise, professional tables showing typical melting (kietas → skystas) diapazonus for common kaltas (kalimas) aliuminio lydiniai ir casting aluminum alloys.
Svarbu: these figures are indicative typical ranges used for process planning and material selection.
Common Wrought / Forging Aluminum Alloys — Typical Melting Range
| Lydinio klasė | Lydymosi diapazonas (° C.) | Lydymosi diapazonas (° F.) | Lydymosi diapazonas (K) | Technical Notes |
| 1050 / 1100 (Commercially pure Al) | ~660.3 – 660.3 | ~1220.6 – 1220.6 | ~933.5 – 933.5 | Near single-point melting due to very high purity. |
| 2024 (Al–Cu) | ~500 – 638 | ~932 – 1180 | ~773 – 911 | Wide freezing range; sensitive to incipient melting. |
| 2014 (Al–Cu) | ~500 – 638 | ~932 – 1180 | ~773 – 911 | Panašus į 2024; higher Cu content affects hot workability. |
| 5083 (Al–Mg) | ~570 – 640 | ~1058 – 1184 | ~843 – 913 | Elevated melting range due to Mg; Puikus atsparumas korozijai. |
| 5454 (Al–Mg) | ~595 – 645 | ~1103 – 1193 | ~868 – 918 | Often used in pressure vessels and tanks. |
6061 (Al–Mg–Si) |
~555 – 650 | ~1031 – 1202 | ~828 – 923 | Widely used structural alloy; melting range critical for heat treatment. |
| 6082 (Al–Mg–Si) | ~555 – 650 | ~1031 – 1202 | ~828 – 923 | Higher strength version of 6xxx series. |
| 7075 (Al–Zn–Mg–Cu) | ~477 – 635 | ~891 – 1175 | ~750 – 908 | Very wide melting range; prone to localized melting. |
| 3003 (Al–Mn) | ~640 – 660 | ~1184 – 1220 | ~913 – 933 | Melting behavior close to pure aluminum. |
Common Casting Aluminum Alloys — Typical Melting Range
| Lydinio klasė | Lydymosi diapazonas (° C.) | Lydymosi diapazonas (° F.) | Lydymosi diapazonas (K) | Technical Notes |
| Al–Si eutectic (~12.6% Si) | ~577 – 577 | ~1070.6 – 1070.6 | ~850.1 – 850.1 | Eutectic composition with a sharp melting point. |
| A356 / AlSi7Mg | ~558 – 613 | ~1036 – 1135 | ~831 – 886 | Excellent castability and heat-treatable. |
| A357 (modified A356) | ~555 – 605 | ~1031 – 1121 | ~828 – 878 | Improved strength and fatigue resistance. |
| A380 (Al–Si–Cu) | ~515 – 585 | ~959 – 1085 | ~788 – 858 | Standard die-casting alloy with low liquidus temperature. |
319 (Al–Si–Cu) |
~525 – 605 | ~977 – 1121 | ~798 – 878 | Good balance of castability and mechanical strength. |
| ADC12 (JIS die casting alloy) | ~500 – 580 | ~932 – 1076 | ~773 – 853 | Widely used die-casting alloy; impurity control is critical. |
| AlSi9Cu3(Fe) | ~510 – 600 | ~950 – 1112 | ~783 – 873 | Versatile casting alloy for complex geometries. |
| A413 (high-silicon alloy) | ~560 – 620 | ~1040 – 1148 | ~833 – 893 | Suitable for high-temperature and pressure-tight castings. |
3. Precise Measurement Methods of Aluminum’s Melting Point
Accurate measurement of aluminum’s melting point is critical for material characterization and process optimization.
Įprasti metodai yra:
Diferencinė nuskaitymo kalorimetrija (DSC)
DSC is the most widely used method for measuring melting points of metals due to its high precision and sensitivity.
The principle involves heating a small aluminum sample (5–10 mg) and a reference material (inertiškas, Pvz., aliuminio oksidas) at a constant rate (5–10℃/min) while monitoring the heat flow difference between them.
The melting point is determined as the onset temperature of the endothermic peak (corresponding to the fusion process).
DSC can measure melting points with an accuracy of ±0.1℃, making it suitable for high-purity aluminum and alloy analysis.
Visual Observation Method (Capillary Tube Method)
This traditional method involves sealing a small amount of aluminum powder in a capillary tube, which is heated alongside a thermometer in a heating bath (Pvz., silicone oil).
The melting point is recorded when the aluminum powder completely melts into a liquid. While simple and low-cost, this method has lower accuracy (±1–2℃) and is primarily used for qualitative analysis or low-precision applications.
Laser Flash Melting Method
For high-pressure and high-temperature melting point measurements, the laser flash method is employed.
A pulsed laser rapidly heats the surface of an aluminum sample, and the melting process is monitored by optical sensors (Pvz., pyrometers, interferometers).
This method can measure melting points under extreme pressures (iki 10 GPA) with high temporal resolution, providing data for aerospace and nuclear applications.
Electrical Resistance Method
Aluminum’s electrical resistance changes significantly during melting (liquid aluminum has higher resistance than solid aluminum due to disrupted electron conduction).
By measuring the resistance of an aluminum wire as it is heated, the melting point is identified as the temperature where the resistance exhibits a sudden increase.
This method is suitable for in-situ monitoring during industrial processes (Pvz., suvirinimas, liejimas).
4. Industrial Implications of Aluminum’s Melting Point
Aluminum’s moderate melting point is a key factor driving its widespread industrial application, as it balances processability and performance:
Liejimo procesai
The melting point of aluminum (660℃) is significantly lower than that of ferrous metals, enabling energy-efficient casting:
- Mirti liejimas: Al-Si eutectic alloys (melting range 577–600℃) are widely used in die casting, as their low melting temperature reduces die wear and energy consumption, allowing high-volume production of complex components (Pvz., automobilių variklių dalys, elektroniniai korpusai).
- Smėlio liejimas: Pure aluminum and low-alloy aluminum are cast in sand molds, with pouring temperatures typically 50–100℃ above the liquidus temperature (700–750℃) to ensure complete filling of the mold cavity.
Heat Treatment and Welding
- Terminis apdorojimas: The melting point of aluminum limits the maximum temperature of heat treatment processes.
Pavyzdžiui, solution heat treatment of 6xxx series alloys is conducted at 530–570℃—well below the solidus temperature (580℃)—to avoid partial melting (deginimas) iš lydinio. - Suvirinimas: Aluminum welding requires heat sources that can rapidly reach the melting point while minimizing thermal distortion.
Common methods include TIG welding (arc temperature ~6000℃) and MIG welding, with welding temperatures controlled at 660–700℃ to ensure fusion of the base metal without excessive grain growth.
Aukštos temperatūros programos
Aluminum’s melting point imposes limitations on its high-temperature use: pure aluminum retains only 50% of its room-temperature strength at 200℃ and softens significantly above 300℃.
To expand its high-temperature applicability, legiravimo elementai (Pvz., Nikelis, kobaltas) are added to form high-melting intermetallic compounds, extending the service temperature of aluminum alloys to 300–400℃ (Pvz., 2618 alloy for aerospace engine components).
Recycling of Aluminum
The moderate melting point of aluminum makes it highly recyclable.
Recycled aluminum requires only 5% energijos, reikalingos pirminiam aliuminiui gaminti, as melting scrap aluminum (at 660–700℃) consumes far less energy than extracting aluminum from bauxite.
This energy efficiency, driven by aluminum’s melting characteristics, makes it one of the most recycled metals globally.
6. Comparative Analysis with Other Metals and Alloys
| Metalas / Lydinys | Lydymosi taškas (° C.) | Lydymosi taškas (° F.) | Lydymosi taškas (K) | Key Notes |
| Aliuminis (Al, grynas) | 660.3 | 1220.6 | 933.5 | Žema lydymosi temperatūra; excellent for lightweight casting and forming. |
| Vario (Cu, grynas) | 1085 | 1985 | 1358 | Aukštas šilumos laidumas; requires higher processing temperatures than Al. |
| Lygintuvas (Fe, grynas) | 1538 | 2800 | 1811 | Significantly higher melting point; widely used in steelmaking. |
| Plienas (Anglies plienas, ~0.2%C) | 1425–1540 | 2600–2800 | 1698–1813 | Melting range depends on composition; higher than aluminum alloys. |
| Titanas (Iš, grynas) | 1668 | 3034 | 1941 | Didelis stiprumo ir svorio santykis; refractory behavior. |
Magnis (Mg, grynas) |
650 | 1202 | 923 | Slightly lower than Al; highly reactive and lightweight. |
| Cinkas (Zn, grynas) | 419.5 | 787 | 692.7 | Žema lydymosi temperatūra; used for die-casting and galvanizing. |
| Nikelis (Į, grynas) | 1455 | 2651 | 1728 | Puikus atsparumas korozijai; high melting point alloys for aerospace. |
| Žalvaris (Cu–Zn, 60/40) | 900–940 | 1652–1724 | 1173–1213 | Alloyed melting range lower than pure Cu; suitable for casting. |
| Bronza (Cu–Sn, 88/12) | 950–1050 | 1742–1922 | 1223–1323 | Slightly lower than copper; improved castability and corrosion resistance. |
6. Misconceptions and Common Pitfalls
Confusing Melting Point with Softening Temperature
The softening temperature of aluminum (≈300℃) is often mistaken for its melting point.
Softening refers to the reduction in yield strength due to grain boundary sliding and dislocation movement, while melting involves a phase transition.
This confusion can lead to improper heat treatment, resulting in reduced mechanical properties.
Ignoring Melting Range in Alloys
Pure aluminum has a sharp melting point, but aluminum alloys exhibit a melting range (liquidus to solidus).
Failing to account for this range during casting can cause defects such as shrinkage porosity (if poured too close to the solidus temperature) or hot cracking (if cooled too rapidly across the melting range).
Overlooking Impurity Effects
Even trace impurities (Pvz., 0.1% lygintuvas) can lower aluminum’s melting point and increase its melting range.
In high-precision applications (Pvz., aviacijos ir kosmoso komponentai), strict control of impurity content is essential to ensure consistent melting behavior and final product quality.
7. Išvada
The melting point of aluminum (660.32℃ for pure aluminum) is a fundamental property rooted in its atomic structure and metallic bonding, serving as a cornerstone for its processing and application.
Multiple factors—including purity, legiravimo elementai, external pressure, and thermal history—modify its melting behavior, enabling the design of aluminum alloys tailored to diverse industrial needs.
From low-temperature die casting of Al-Si alloys to high-strength 7xxx series alloys for aerospace, the melting point of aluminum dictates process parameters, performance limits, and recycling efficiency.
As industries pursue lightweighting and energy efficiency, aluminum’s unique balance of moderate melting point, mažas tankis, and recyclability will continue to solidify its position as a key material in the global manufacturing landscape.
DUK
Is aluminum’s melting point temperature the same for 6061 arba 7075?
Ne. 6061 ir 7075 are alloys with solidus/liquidus ranges that differ from pure Al. Their melting behaviour must be referenced to alloy-specific data or measured by thermal analysis.
How much superheat should I use for die casting vs. Smėlio liejimas?
Die and high-pressure processes often require moderate superheat (20–50 °C) because of rapid filling; sand and thicker-section castings may require higher effective superheat (40–100 ° C.) to ensure complete filling. Optimize for the alloy and mold.
Why is hydrogen porosity worse in aluminum?
Hydrogen solubility in liquid aluminum is much higher than in solid. During solidification hydrogen is rejected and forms gas pores unless removed beforehand by degassing.
Does pressure change aluminum’s melting point in practice?
The melting point shifts with pressure, but for standard atmospheric foundry practice the effect is negligible.
