what is the Differences 6061 Aluminum vs. 7075 Aluminum in Properties, Strength,Uses and Application

what is the Differences 6061 Aluminum vs. 7075 Aluminum

 

There are many considerations when choosing an alloy for a project. Aluminum alloys are metals made primarily of aluminum with added alloying elements to increase the base aluminum’s capabilities. These include increased strength, corrosion resistance, conductivity, etc., or a blend of these traits. There are dozens of aluminum alloys that have been specially developed for these benefits, so there are many choices when specifying the best alloy for your application. This article will compare 6061 aluminum alloy and 7075 aluminum alloy, two common aluminum types that are widely used in industry (for more information, feel free to visit our articles all about 6061 and 7075 aluminum alloys, respectively). The differences in properties, strengths, and uses will investigated, so as to show where each of these alloys excels, as well as where they should not be specified.

6061 Aluminum alloy

Type 6061 aluminum is from the 6xxx class of aluminum, which include those alloys that use magnesium and silicon as their primary elements. The elemental composition of 6061 aluminum alloy is as follows: 0.6% Si, 1.0%Mg, 0.2%Cr, 0.28% Cu, and 97.9% Al. The copper content of type 6061 makes it somewhat susceptible to corrosion; however, this effect is not as significant as other copper-laden alloys. The density of 6061 aluminum alloy is 2.7 g/cm3 (0.0975 lb/in3), or about the same as pure aluminum metal. This alloy can be strengthened using the heat treatment process (more information on this topic can be found in our article all about 2024 aluminum). Some of the most common tempers of 6061 aluminum are 6061-T6 and 6061-T4, but buyers can specify the exact method with which it is strengthened, if at all. 6061 aluminum has good formability, excelling in extrusion projects, and is easily joined via welding. Its moderately high strength and its fair resistance to corrosion allow type 6061 aluminum to be a great general-purpose alloy, with many applications in structural materials, welded assemblies, piping, fasteners, electronic parts, and many more.

7075 Aluminum alloy

7075 aluminum alloy is part of the 7xxx series, where zinc is used the primary alloying element, though auxiliary elements are often used as well. Its nominal chemical breakdown is 90.0% Al, 5.6% Zn, 2.5%Mg, 0.23%Cr, and 1.6% Cu. Because 7075 has >1% Cu, it is more affected by caustic environments and does not share the high corrosion resistance which other aluminum alloys have. This is a necessary disadvantage, as the high copper content helps make this alloy exceptionally strong. The density of 7075 aluminum is slightly larger than pure aluminum at 2.81 g/cm3 (0.102 lb/in3), and it can also be strengthened using the heat treatment process (the most common temper being 7075-T6). This alloy is one of the strongest types of aluminum available, yet is difficult to form and weld and it is more easily degraded by corrosive effects. These downsides are justified by 7075 aluminum’s impressive strength, where it excels in high-stress environments as found in the aerospace industry, high-wear parts, structural materials, and military applications.

Comparing 6061 & 7075 Aluminum alloys

Below is a comparison of some material properties between 6061 and 7075 aluminum alloys, so as to highlight the differences between them. For the simplicity of understanding, this article has chosen to compare the same heat-treatment method for both alloys (6061-T6 and 7075-T6), but know that the below values change based on how the alloy is strengthened. These properties will be briefly explained, but are summarized in Table 1 for facilitating viewing.

Comparison of material properties between 6061 & 7075 aluminum alloys

The yield strength is the measure of the maximum amount of stress that will not permanently (or just “elastically”) deform a specimen of alloy (to learn more on this topic, feel free to read about it in our article all about 7075 aluminum alloy). When comparing 6061 and 7075 aluminum’s yield strengths, it is evident that 7075 aluminum is far superior by a factor of almost 2. This is a consequence of 7075’s chemical composition, as well as the result of heat treating. However, 6061 alloy is not to be thought of as weak, as a yield strength of 276 MPa is only slightly less than some low carbon steels.

The modulus of elasticity is a measure of a material’s resistance to permanent (or “plastic”) deformation. It is useful as a means of defining the “stiffness” of a material. There is a small difference when comparing the moduli of these alloys, which suggests that these materials behave similarly when elastically deformed.

The thermal conductivity of a material is a measure of how well heat is transferred through the material (or how well it can “conduct” heat). A large thermal conductivity (as seen in these metals) suggests that they conduct heat readily and are not insulating materials. Note that these values are derived from empirical tests and fluctuate based on heat treatment, alloy composition, and other factors. Since 6061 aluminum’s thermal conductivity is generally higher, it is better suited for heat-dissipative applications (such as heat sinks and heat exchangers) than 7075 aluminum is, though 7075 aluminum’s thermal conductivity is also quite good.

The melting point is the temperature with which the alloy will phase-change from solid to liquid, and they are reported in ranges due to the variance of tempers and elemental compositions, as well as unique phase states. It is interesting to see that, even though 7075 alloy is twice as strong as 6061 alloy, it melts at a slightly lower temperature. This value is useful for the heat treatment process, where these temperatures must sometimes be achieved to equally distribute the alloying elements into the base metal, or in high-temperature applications.

The electrical resistivity is a measure of how well the material resists the transfer of electricity. It is the inverse of electrical conductivity which works in much the same way that thermal conductivity does, but with electrical charge and not heat. Both of these alloys have low resistivity, suggesting high conductivity, and are therefore conductive materials useful in electrical applications. 6061 is generally more suited for these uses, as it is more widely available, can be formed and welded easier, and is slightly more conductive than 7075 aluminum.

The hardness of a material is its response to local indentation from a standardized force; in this instance, it is found using a 500g force imparted by a 50mm ball onto the metal. Know that there are many different scales that quantify hardness, but this article highlights the more common Brinell scale. For reference, the Brinell hardness for glass (a very hard material) is 1550, while lead (a soft material) has a Brinell hardness of 5. Hardness is an important measure, as a harder material tends to fail more easily by brittle fracture, so a balance must be found between hardness and ductility. Both of these alloys are hard enough to withstand easy deformation, but ductile enough to not shatter/crack easily, making them both excellent choices for building materials. If one had to be chosen for its hardness, 7075 aluminum should be specified as it is generally harder than type 6061 alloy.

The machinability of a material is a measure of how it reacts to machining procedures such as milling, cutting, die-casting, etc., and is calculated using tooling speed, surface finish, and tool life when machining a specific alloy. Just as hardness has numerous ways to be defined, so does machinability, so this article provides a qualitative assessment (excellent/good/fair/poor) to avoid confusion. Both of these alloys can be machined without much trouble, but 6061 aluminum is the preferred choice if machinability is of some concern. Note that neither of these alloys should be chosen if machinability is a priority, as certain alloys such as type 2011, 2007, and 3003 respond well to machining and should be chosen over these two alloys.

 

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