Aluminum is one of the most durable and versatile metals available today. Not only does it have an amazing strength-to-weight ratio that beats out just about any other option, but it’s also resistant to corrosion, easy to fabricate and highly recyclable. While not quite as strong as steel, it weighs significantly less, making it highly desirable for applications where strength and weight are important considerations. That’s why aluminum is a valuable option in industries such as aerospace, transportation and consumer electronics.
You might find that some aluminum alloys aren’t strong enough for your needs. Fortunately, manufacturers and designers have several options when it comes to aluminum grades. With a little education, you can choose your aluminum alloys to make your products more durable and impact resistant, while retaining the other great properties that make aluminum an attractive material.
Today, we’ll go over some of the options for alloying aluminum and discuss which ones might be right for particular applications.
How alloying aluminum makes it stronger
Standard aluminum alloys are approximately one third the weight of steel. That’s amazing when you consider that through alloying and other strengthening options, it is possible to create high performance aluminum that approaches the strength of steel. It’s also quite strange given the fact that pure aluminum, while highly flexible, is not very strong and has few commercial applications. Therefore, the first step to having quality, high-strength aluminum is to alloy it with other elements.
The reason aluminum was first able to become such an important metal was due to early experiments by chemists and engineers of the late 19th and early 20th century. When pure aluminum is combined with other metals and elements, its chemical composition undergoes fundamental changes that strengthen it. Anytime you buy aluminum from a material supplier, it will be one of the many commercially available alloys. Since each alloy is unique, with significantly different properties, it’s essential you know which alloy is best suited for your application.
Some of the frequent alloying elements for aluminum include silicon, magnesium, manganese, zinc, molybdenum and copper. Among the strongest of these alloys are the aluminum-zinc grades. Keep in mind that while strength is one consideration when alloys are created, adding additional elements affects the metal’s other properties, such as density, workability, conductivity and corrosion resistance.
If you’re new to aluminum, the various alloys are identified based on a four-digit numbering system, with the first digit designating its general class based on the primary alloying element. The 2xxx series has copper as its principle alloying agent, the 6xxx series has both silicon and magnesium, and the 7xxx series, often among the strongest aluminum alloys, has zinc.
How heat treatment can strengthen aluminum
Another way to make aluminum stronger is through the heat treatment process. This process works with a subset of aluminum alloys that are precipitation hardenable, a category that includes the 2XXX, 6XXX, 7XXX and 8XXX series.
The precipitation hardening process involves changes in solid solubility paired with heat, generating fine particles during an impurity phase within the metal’s atomic crystalline lattice. This altering of the metal’s structural atomic composition serves to strengthen it. The metal must be heated several hours for the precipitation to occur. A common name for this process is natural aging, and when combined with a solution treatment, it’s known as STA.
Another alternative for heat treating aluminum is known as annealing. This is especially suitable for metal that has undergone strain hardening, which is a kind of plastic deformation that leads to an alteration to the grain structure. Annealing can restore the original (or something approximating the original) grain structure of the alloy. This will allow for shaping of the metal without excess force.
The process of annealing involves heating the previously work hardened aluminum alloy to between 570°F and 770°F for anywhere from thirty minutes to three hours. The exact settings will depend on which alloy is involved and how big the workpiece is.
Work hardening is another option for strengthening aluminum
As already mentioned, work hardening, sometimes referred to as strain hardening, is also used to strengthen aluminum. It involves plastic deformation of the metal, which leads to dislocations in the grain structure. Basically, the more dislocations there are, the harder it is to create more dislocations, so work hardening is a way of boosting the overall strength of the aluminum. It is important to note that the increase in strength is accompanied by a decrease in ductility.
The ways in which work hardening is normally accomplished involves shaping the metal at a temperature that is below its recrystallization temperature, normally room temperature. The actual process can involve forging, bending, drawing or rolling the aluminum. Cold working will generally lead to an increase in the hardness, yield strength and tensile strength of the metal.
What does the future hold?
Engineers are constantly looking for new techniques for increasing the strength of aluminum alloys. A recent example is known as high-pressure torsion, colloquially referred to as metal smashing. (https://www.sciencemag.org/news/2010/09/metal-smasher-makes-aluminum-strong-steel) This is when a thin disk of metal is clamped to an anvil and then pressed between another anvil at a force of approximately 60,000 kilograms per square centimeter. At the same time, one of the anvils slowly rotates. The metal is then allowed to rest for one month at room temperature to undergo the process of natural aging. Tests conducted with 7075 resulted in the alloy attaining a strength of 1 gigapascal, more than three times stronger than conventional aluminum.
With these kinds of advances on the horizon, just imagine what will be possible with aluminum.
Work with a technical services professional
Thanks to these ongoing developments, today’s aluminum is more durable, adaptable and environmentally sustainable than ever before. In order to ensure you have the most advanced and effective aluminum solutions, you need to work with a supplier who does more than just ship raw materials. At Clinton Aluminum, our philosophy is to always find the right material for the job. Contact us today to learn more about which aluminum alloy is right for you.