If you’ve ever wondered what properties of aluminum make it such a popular and versatile metal, you’re not alone. There are numerous characteristics that make aluminum and aluminum alloys one of the world’s most important materials in use across an impressive range of industries. This includes the appliance, architectural, aviation, and automotive industries, just to name a few.
Examining the physical, chemical, and mechanical properties of a material forms the basis of materials science. This makes it possible to predict behavior in particular environments and under stress. Such performance indicators help architects, fabricators, and designers select the correct material for a specific application.
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Many outstanding properties of aluminum and aluminum alloys lead to a wide range of applications. For instance, of all metals, aluminum alloys are among the easiest to form and machine. Aluminum’s mechanical properties make it so. What other attributes drive the preference for aluminum products and materials?
The Major Properties of All Metals
Metals make up a majority of the elements on the periodic table. They are a class of elements distinguished by the following properties: ductility, malleability, hardness, conductivity, the ability to form alloys, and qualities of appearance.
These properties can be grouped as either physical, chemical, or mechanical and they can be expanded upon in further depth when considering specific alloy compositions and other factors, like temperature. The charts below refer to pure aluminum.
Material Properties of Aluminum and Aluminum Alloys
Aluminum is a metal-like element with both metal and nonmetallic properties, situated in the boron and carbon family. Though aluminum is one of Earth’s most abundant elements, it must be sourced from bauxite ore and undergo a production process before becoming commercially pure, viable aluminum.
Aluminum is then classified according to alloyed elements in a numbered 4-digit series, 1xxx to 8xxx.
Commonly added elements include copper, magnesium, manganese, silicon, and zinc. With these, hundreds of alloy compositions exist.
These specific alloy compositions affect appearance and fabricability. The addition of elements improves strength, workability, corrosion resistance, electrical conductivity, and density compared with pure aluminum.
Physical properties of aluminum relate to the observable form and structure, before any chemical alteration.
|The Physical Properties of Aluminum
|Color and State
||Solid, nonmagnetic, non-lustrous, silvery-white with slight bluish tint.
||Aluminum has a face-centered cubic structure that is stable up to melting point.
||Aluminum surfaces can be highly reflective.
||Commercially pure aluminum is soft. It is strengthened when alloyed and tempered.
||High ductility. Aluminum can be beaten very thin.
||High malleability. Aluminum is very capable of being shaped or bent.
||Aluminum has a thermal expansion coefficient of 23.2. This is between zinc—which expands more—and steel, which expands half the range of aluminum.
||Good electrical and thermal conductor.
||Aluminum is corrosive resistant due to a self-protecting oxide layer.
||Aluminum has a low density, measured by gravity in comparison to water, of 2.70. Compare this to the density of iron/steel which has a density of 7.87
|Melting Point and Boiling Point
||Commercially pure aluminum has a melting point of approximately 1220°F and a boiling point of approximately 4,478°F. These change once aluminum is alloyed.
Takeaways for Physical Properties of Aluminum
Physical properties of aluminum help make sense of its applications. Looking at the chart above, we see that aluminum displays a good combination of strength, resistance to corrosion, and ductility. This helps explain how aluminum can exist in the form of foil and beverage cans, as well as piping and irrigation tubing.
Polished aluminum shows good reflectance over a broad range of wavelengths, which leads to its selection for a variety of decorative and functional uses, including appliances and lasers.
That aluminum is nonferromagnetic makes it suitable for electrical and electronics industries. The thermal conductivity of aluminum alloys is advantageous in heat exchangers, evaporators, electrically heated appliances and utensils, as well as automotive rims, cylinder heads, and radiators.
Its face-centered cubic structure contributes to excellent formability. Aluminum is also nontoxic and often used in food and beverage containers. According to The Aluminum Association it is also among the easiest to recycle of any of the structural materials.
A substance’s characteristic or behavior as it undergoes a chemical change or reaction. In other words, a substance’s atoms must be disrupted for the chemical properties to be observed. Observations of this disruption at the atomic level take place during and also following the reaction.
|The Chemical Properties of Aluminum
||Aluminum occurs as a compound, principally found in bauxite ore.
||Aluminum combines with oxygen to form aluminum oxide when exposed to moist air.
||When aluminum is in a powdered form it will catch fire easily if exposed to flame.
|Ability to form alloys
||Hundreds of aluminum alloy compositions exist. Alloyed elements include: iron, copper, manganese, silicon, magnesium, and zinc.
|Reactivity with water
||Aluminum reacts quickly with hot water.
|Reactivity with alkalis
||Reactive with sodium hydroxide.
|Reactivity with acid
||Aluminum reacts with hot acids.
Takeaways for Chemical Properties of Aluminum
In some ways, the chemical properties of aluminum are unusual compared to other metals. For example, reactivity to both bases and acids is uncommon for metals. This becomes a factor worth considering when aluminum is used as a container for liquids. You have to be certain the aluminum will not dissolve. Hence why beverage cans have a thin liner to prevent corrosion.
Another quirky fact about aluminum is that aside from its powdered form, aluminum is nonpyrophoric. This means that in its powdered state, aluminum is flammable and considered a dangerous hazard, especially during processing when fine dust particles are common.
That aluminum combines so easily with oxygen directly impacts welding practices. The firm oxide layer that forms on the surface of aluminum melts at triple the temperature as the aluminum underneath. Therefore, deep intentional surface cleaning usually with acetone is needed prior to weld, and alternating current is required throughout the welding process.
Mechanical properties note a materials relationship between stress and strain and measure the degree of elasticity in response to an applied load.
|The Mechanical Properties of Aluminum
|Elasticity in tension
||Aluminum has a Young’s modulus of 10000 ksi. Compare this to copper at 17550 ksi or wood at 1595 ksi.
|Tensile strength ultimate
|Bearing yield strength
|Elongation at break
Takeaways for Mechanical Properties of Aluminum
Mechanical properties bear significantly on performance applications. This is particularly true when you consider how mechanical properties vary among aluminum alloys.
For instance, the trend for elongation across the aluminum alloy series is high for lower series alloys and low for higher series alloys. In other words, when comparing 1xxx series aluminum alloys to 7xxx series alloys, 1xxx series alloys will have significantly higher ductility.
This works inversely with tensile strength, hardness, and impact sensitivity, which will be lower among the lower series alloys. So, in that same comparison, the 1xxx series alloys will show much lower tensile strength, hardness, and impact sensitivity than their 7xxx counterparts.
Elevated temperatures also compromise aluminum even before they reach melting point. As a result, most aluminum alloys are not typically suggested for longtime service at higher temperatures. However, certain alloys have been specifically designed for high-temperature resistance, like the 2xxx aluminum-copper series.
The exceptional ability for aluminum to form alloys expands its reach across industries and applications. Without this essential capability, prime aluminum would be too soft and pliable for applications that require greater strength and durability.
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