Materially Different, Mechanically Similar: HX5® vs. 6061-T6 Aluminum
Typically used for applications where a high strength-to-weight ratio is critical – such as aerospace, defense, advanced transportation, performance recreation, and more – 6061-T6 is a tempered version of the 6061 aluminum alloy, one of the most commonly used aluminum alloys in the world, and features one of the highest tensile strength of all 6061 types. Although this metal is generally considered high-strength and low-weight, engineers – always looking to push the envelope – begged the question: what if there was a material that was just as strong as 6061-T6, but even lighter in weight?
Engineers on the F-35 program at Lockheed Martin appreciated the strength capabilities of 6061-T6, but they knew that a lighter weight material could deliver a more operationally efficient, competitive aircraft. Thus, HX5® was developed, a specially engineered nanocomposite maintaining 93% of the strength profile of 6061-T6 but at 50% the weight. Alpine Advanced Materials quickly realized, however, that HX5 was not only suitable for fighter jets, but also an ideal solution for any moving application that requires durability in the harshest environments.
Although 6061-T6 aluminum can still present a compelling business case for some applications, HX5 can be an even better solution, especially in the long-term. How does one determine which material to use? HX5 is highly characterized, and we have extensive testing data to effectively compare it against any material on the market. In this article, we will explore how some of the mechanical, thermal, and environmental properties of HX5 and 6061-T6 stack up, as well as how each are manufactured.
HX5 and 6061-T6 are very similar in both tensile and compressive strength, but HX5 triumphs in flexural strength. Additionally, for all three of these strength properties, HX5 gets significantly stronger in sub-freezing temperatures, making it ideal for applications subjected to extremely cold climates.
At A Glance: HX5® vs. 6061-T6 Aluminum
|Tensile Strength (73°F, Ksi)||38.2||40|
|Compressive Strength (73°F, Ksi)||43||40|
|Flexural Strength (73°F, Ksi)||53||43.4|
|Specific Strength (lb/in2)/(lb/in3)||741,700||410,300|
|Coefficient of Thermal Expansion (L/L/°F)||2.11 x 106||13.1 x 106|
Examining the materials’ specific strength – or strength-to-weight ratio – can be more telling than the simple strength properties listed above. Measured by dividing the material’s strength by its density, the specific strength indicates how strong the material is per unit of weight. Pound for pound, HX5 dominates 6061-T6, touting almost double the specific strength of its competitor.
Despite its strength, the nanocomposite does not fare as well in high-impact scenarios as the metal. This mechanical property, known as brittleness, determines how prone a material is to break without much permanent distortion beforehand. For certain applications, however, this shortfall may in fact be beneficial. Rather than letting a part silently fail and deteriorate over time, a clear and immediate failure of the component allows operators to replace it without risking future issues.
Alternatively, HX5 stands up incredibly well to common phenomena that lead to component deformation and eventual failure: creep, the slow, permanent deformation that occurs under a steady load over a long period of time; and fatigue, the decrease in load carrying capability or initiation and propagation of cracks in a material due to cyclic loading, which will continue to grow and eventually become a critical size.
Fire & Ice
When subjected to extreme temperatures, HX5 and 6061-T6 aluminum behave rather differently. The coefficient of thermal expansion (CTE) is the rate at which a material expands or contracts due to changes in temperature. Unlike 6061-T6, HX5 has a remarkably low CTE, which makes it ideal for applications that require stability in thermally unstable environments. HX5’s resistance to extreme temperatures also means that it maintains its mechanical properties longer as temperatures increase or decrease. In fact, HX5 gets stronger in colder temperatures.
How “extreme” can these materials actually go? The nanocomposite’s glass transition temperature – the temperature at which the material stiffness begins to decrease at a higher rate (rate varies from material to material) – is 316°F, whereas the metal can begin to lose its strength at a temperature of 392°F. However, HX5's high surface energy means that it is extremely coatable, and any limitation in conductivity or temperature resistance can be addressed with the appropriate coating. At 680°F, HX5 will finally begin to melt, whereas heat can be applied to 6061-T6 up to 1090°F before finally melting.
Protection Against the Elements
Due to their strength and almost impenetrable nature, metals have historically been thought of as the most durable materials available to man. However, an acceleration of advancements in materials science has created a number of composites that also tout impressive environmental properties. For instance, HX5’s impressive abrasion-resistance is similar to many metals. And even though both 6061-T6 and the nanocomposite are largely unaffected by UV radiation – one sliver of the electromagnetic spectrum – HX5 has inherent attenuation, which means it is effective at shielding from electromagnetic interference, a particularly important feature for aerospace and defense communications applications, something uncommon in most non-metallics.
Although 6061-T6 aluminum is moderately corrosion-resistant when treated with protective coatings, HX5 has been tested and proven to be extremely resistant to solvents, fuels, lubricants, and chemicals – as molded, without secondary processes. Additionally, components made with 6061-T6 are at risk of galvanic corrosion when in electrical contact with a dissimilar metal in a non-conducive environment, including a humid open-air environment, whereas components made with HX5 remain unfazed due to its non-metallic nature.
Efficiency in Production
Manufacturing components with 6061-T6 aluminum generally falls into one of three methods: sheet metal manipulation, extrusion, or machining. Manipulating sheet metal – either by bending it, cutting it, or a combination of the two – is inexpensive but limited in design and strength capabilities. Similar in its limitations, extrusion is the process of transitioning the metal to a plastic state and forcing it through a shaped orifice, resulting in a long constant cross-section. Machining on the other hand is a subtractive process which involves cutting away from a billet of metal to reveal a finished part. Although it allows for more design freedom than sheet metal or extruded parts, machining high-complexity components is time consuming and expensive, and quickly multiplied in high volumes.
Alternatively, the primary manufacturing method for HX5 is injection molding, which involves melting the material down to a liquid state and shooting it into a “cool” steel cavity at up to 18,000 psi or higher, resulting in the final molded product. Ideal components for HX5 have complex geometries, and strength is maximized through the alignment of carbon fibers during the injection molding process. Additionally, HX5’s low viscosity allows it to flow in very thin sections, facilitating incredibly intricate designs. Taking only seconds to complete, injection molding is much faster than metallic manufacturing, and HX5’s highly repeatable nature means that Part #1 will be identical to Part #1000. Although the upfront costs for developing a steel mold can be daunting, high-quantity production makes it easier, especially if amortizing the cost of the tool over production volumes.
Which Material Wins?
The determinant of a material's value ultimately lies in the specific application. No material is "better" or "worse" without the lens. Being armed with high-quality options ensures that your company can make the future-forward decisions necessary to maintain a competitive advantage.