Aluminum is a lightweight, silvery-white metal with a density of about 2.70 g/cm³, making it roughly one-third the weight of steel. It sits at atomic number 13 on the periodic table, and its combination of low density, high conductivity, and corrosion resistance makes it one of the most widely used metals on Earth.
Density and Weight
At 2.70 g/cm³, aluminum is remarkably light for a structural metal. Steel comes in at about 7.8 g/cm³ and copper at 8.96 g/cm³, so aluminum weighs roughly a third of either. This low density is the main reason it dominates in aerospace, automotive, and packaging applications where every gram matters. Despite being light, aluminum is strong enough to form structural beams, aircraft fuselages, and engine components when alloyed with small amounts of other metals like copper, magnesium, or zinc.
Melting and Boiling Points
Pure aluminum melts at 660 °C (1,220 °F) and boils at 2,327 °C (4,221 °F). The melting point is low enough that aluminum can be cast and welded with standard industrial equipment, which contributes to its popularity in manufacturing. For context, steel melts between 1,370 and 1,530 °C, so aluminum requires significantly less energy to process. The wide gap between its melting and boiling points means molten aluminum stays liquid across a broad temperature range, giving manufacturers flexibility during casting and forming.
Thermal and Electrical Conductivity
Aluminum conducts heat at 237 W/m·K, placing it among the best thermal conductors of all common metals. Only copper (about 400 W/m·K) and silver significantly outperform it. This thermal conductivity is why aluminum shows up in heat sinks, cookware, radiators, and heat exchangers. It pulls heat away from sources quickly and distributes it evenly.
Electrically, aluminum carries about 61% of copper’s conductivity. That sounds like a disadvantage until you factor in weight: because aluminum is so much lighter, a pound of aluminum actually conducts about twice as much electricity as a pound of copper. This is why overhead power lines are almost universally made from aluminum rather than copper. The tradeoff works out strongly in aluminum’s favor whenever weight matters more than volume.
Reflectivity
Polished aluminum reflects about 92% of visible light and performs well across infrared and ultraviolet wavelengths too. Only silver, at roughly 97% reflectivity, does better among common metals. This broad-spectrum reflectivity makes aluminum the standard material for telescope mirrors, solar reflectors, LED lighting housings, and the reflective coatings inside food packaging. Thin aluminum films achieve about 90% total reflectivity, which is why aluminum foil has that characteristic bright, mirror-like surface on one side.
Crystal Structure
At the atomic level, aluminum arranges itself in a face-centered cubic (FCC) crystal structure. In this arrangement, atoms sit at each corner of a cube and at the center of each face. FCC metals tend to be ductile and easy to work with because their atomic planes can slide past each other in multiple directions. This is a big part of why aluminum can be rolled into thin foil, drawn into wire, or stamped into complex shapes without cracking. Copper, gold, and silver share this same crystal structure, and all of them are known for being soft and highly workable.
Specific Heat Capacity
Aluminum has a specific heat capacity of 0.89 J/g·°C, which is unusually high for a metal. Steel’s specific heat is about 0.50 J/g·°C, and copper’s is 0.39 J/g·°C. In practical terms, this means aluminum absorbs a lot of thermal energy before its temperature rises significantly. A block of aluminum takes roughly twice as much heat energy to warm up as the same mass of steel. This property is useful in applications like engine parts and brake components, where the material needs to soak up heat without overheating quickly.
Magnetic Behavior
Aluminum is paramagnetic, meaning it has an extremely weak attraction to magnetic fields. Its magnetic susceptibility is about +2.2 × 10⁻⁵, which is so low that aluminum behaves as essentially non-magnetic in everyday life. A refrigerator magnet will not stick to aluminum. This near-zero magnetic response is why aluminum is used in electronics housings, MRI-compatible medical devices, and scientific instruments where magnetic interference would be a problem.
Natural Isotopes
Aluminum has only one stable isotope: aluminum-27, which accounts for virtually 100% of all naturally occurring aluminum. A radioactive isotope, aluminum-26, exists in trace amounts in nature with a half-life of about 720,000 years, but it plays no role in the metal’s everyday properties. Having a single dominant isotope is relatively unusual among elements and means that aluminum samples are chemically and physically consistent regardless of where they’re sourced.
Corrosion Resistance
When exposed to air, aluminum instantly forms a thin oxide layer on its surface, typically just a few nanometers thick. This layer is hard, transparent, and chemically stable, and it bonds tightly to the underlying metal. Unlike iron rust, which flakes off and exposes fresh metal to continued corrosion, aluminum oxide stays firmly in place and acts as a protective barrier. If the surface gets scratched, the oxide layer reforms almost immediately. This self-healing behavior is why untreated aluminum can last decades outdoors without significant degradation, and it can be enhanced further through anodizing, a process that thickens the oxide layer artificially.