6061 vs. 7075 Aluminum: Which One Is Better for Your Project?

In our daily lives, we interact with various metal materials all the time. Have you ever wondered what metal your smartphone's casing is made of? Or why cars and bicycles are so lightweight yet strong? The answer to these questions often lies in a metal we often overlook but that plays a crucial role — aluminum.

Aluminum and its alloys are renowned for their properties such as lightness, high ductility, good corrosion resistance, high electrical and thermal conductivity, ease of recycling and excellent machinability. They are not only crucial materials for manufacturing electronic products and vehicles, but are also widely used in construction, packaging, and aerospace industries.

Among the aluminum alloy family, 6061 and 7075 aluminum are particularly popular due to their excellent performance. So, what are the advantages and characteristics of these two aluminum alloys? What are the differences between them? In this article, we will reveal the answers one by one.

An Overview of 6061 Aluminum

6061 Aluminum, derived from the 6XXX series, is the most common general-use aluminum alloy. It contains magnesium, silicon, and iron as its main alloying elements, which contribute to a good balance of strength, toughness, and ductility. 6061 aluminum exhibits excellent formability,weldability, and machinability. Additionally, it has excellent corrosion resistance, even when the surface is scratched. If further protection is needed, it can be anodized to add a thin protective layer, which can be available in various colors.

6061 aluminum also has excellent heat treatability. Common heat-treated conditions like T4, T6, and T651 can significantly enhance its mechanical properties, improving its performance and making it more suitable for specific applications.

It is worth mentioning that within the 6XXX series of aluminum alloys, 6063 is also a popular choice, with magnesium and silicon as its main alloying elements. It offers excellent formability and surface finish, making it highly preferred for extrusion processes. However, its strength is only about half that of 6061, so it is mainly used in architectural and decorative applications where high strength is not critical, such as window frames and decorative door frames.

Application of 6061 Aluminum

6061 aluminum is widely used in various structural and engineering applications requiring certain strength and high corrosion resistance, such as:

• Construction of bridges, roofs, and other structural elements.
• Automotive components such as car frames, chassis, and wheels.
• Hulls, decks, and other structural components in boat and shipbuilding.
• Electrical connectors, heat sinks, and housings in electronic devices.
• Precision machined parts, tools, and fixtures.
• Sporting goods like camping gear, fishing rods, and hiking poles.

An Overview of 7075 Aluminum

7075 aluminum, derived from the 7XXX series, comprises copper and zinc as its main alloying elements. It is known for its superior fatigue resistance and is one of the highest-strength aluminum alloys available, comparable to many steels. Despite7075 aluminum alloy is also highly heat-treatable, enabling it to achieve extremely high strength and varying degrees of resistance to stress corrosion cracking through heat treatment. Common heat-treated conditions include T6, T651, T73, and T76. its high strength, 7075 maintains good machinability and can be machined to tight tolerances, though it requires more power and specific tooling compared to 6061. However, 7075 is a poor choice for welding and is not as corrosion-resistant as 6061, often requiring protective coatings and coming at a higher cost.

7075 aluminum alloy is also highly heat-treatable, enabling it to achieve extremely high strength and varying degrees of resistance to stress corrosion cracking through heat treatment. Common heat-treated conditions include T6, T651, T73, and T76.

Application of 7075 Aluminum

7075 Aluminum is mainly used in high-performance structural and engineering applications that demand exceptional strength-to-weight ratio and and fatigue resistance, particularly in：

• Aircraft structures, including wings, fuselage frames, and other critical components.
• Military hardware, such as armor plating, weapons, and missile components.
• High-performance sporting goods, like high-end bicycles, rock climbing equipment, and competitive sports gear.
• Braking systems, engine supports, frames, wheel hubs, and other parts of automobiles, trains, and ships.
• Die-casting dies, extrusion dies, precision processing equipment, automation equipment, and other machinery manufacturing.

Properties Comparison: 6061 vs. 7075 Aluminum

Next, we’ll differentiate these two alloys from their chemical compositions, density, mechanical properties, chemical characteristics, weldability, and cost.

Composition

In 6061 Aluminum alloy, Magnesium (Mg) combines with Silicon (Si) to form Mg2Si precipitates, which significantly enhances the alloy's strength.

In 7075 Aluminum alloy, Zinc (Zn) is the primary alloying element, with its content up to 5.6% responsible for the alloy's remarkable strength and hardness, making it suitable for high-stress applications. Mg is to interact with Zn and Cu to form strengthening precipitates, enhancing the alloy's exceptional strength. Si's effects are overshadowed by Zn and Mg in 7075, with its primary role being more related to refining the grain structure during casting.

Density

Aluminum and its alloys are lightweight and have relatively similar densities. Specifically, 6061 and 7075 aluminum alloys contain high amount of aluminium, and other specific amount of metal materials with different densities. So the densities of the two alloys just vary a little, measuring approximately 2.7 g/cm³ and 2.81 g/cm³ respectively.

This slight variation of densities underscores the alloy's fundamental composition and contributes to its widespread adoption in various industries where weight reduction is crucial.

Mechanical Properties

To get an intuitive comparison, we have compiled the data into the following table, comparing the most commonly used heat-treated state T6, for both 6061 and 7075 aluminum alloys.

Yield Strength

Yield strength refers to the maximum stress that a material can withstand before undergoing permanent plastic deformation. Beyond this point, the material will not return to its original shape when the stress is removed. The yield strength of 7075 Aluminum is much higher than that of 6061, which is mainly attributed to the higher content of zinc and magnesium in 7075 Aluminum.These elements form strengthening precipitates that greatly enhance the strength of the alloy.

Although 6061 aluminum also improves its strength through heat treatment and precipitation hardening, its main alloying elements, magnesium and silicon, are present in lower quantities, resulting in relatively lower strength. However, 6061 aluminum should not be considered fragile, as its yield strength of 276 MPa is only slightly lower than that of some low carbon steels.

Modulus of Elasticity

Modulus of elasticity is a measure of the stiffness of a material. It is the ratio of stress to strain within the elastic limit, representing the material's ability to resist deformation under an applied load. A higher modulus of elasticity indicates a stiffer material that is less prone to deformation under stress.

7075 and 6061 have similar moduli of elasticity (71.7 GPa vs. 68.9 GPa). This is because the modulus of elasticity is primarily determined by the atomic bonding within the material, rather than the specific alloying elements or heat treatment processes used to produce the alloys.

Thermal Conductivity

Though all forms of aluminum alloys are good thermal conductors,different alloying elements can alter the microstructure of aluminum, thereby affecting its thermal conductivity. 6061 aluminum alloy has a higher thermal conductivity (167 W/m·K), primarily because its alloying elements, magnesium and silicon, have a minimal impact on the thermal conductivity of the aluminum matrix. In contrast, 7075 aluminum alloy has a lower thermal conductivity (130 W/m·K) due to its high content of zinc and copper. These elements form complex compounds and precipitates that scatter heat flow, thereby reducing the overall thermal conductivity.

Hardness

The hardness of 7075 aluminum alloy is generally higher than that of 6061. In 7075 aluminum, the high content of zinc and magnesium facilitates the formation of numerous MgZn2 precipitates, which are exceptionally hard, thereby significantly improving the overall hardness of 7075 aluminum. The presence of copper further amplifies this effect. Even though copper alone contributes minimally to hardness, its interaction with zinc and magnesium elevates the material's mechanical properties.

Conversely, in 6061 aluminum, the Mg2Si precipitates formed by magnesium and silicon do improve hardness, but due to their lower content, the improvement is limited.The T6 temper of 6061 aluminum is particularly designed to balance strength and workability.

Machinability

Both 6061 and 7075 aluminum alloys possess commendable machinability traits. However, higher hardness and strength generally make cutting and shaping more difficult, increasing the difficulty of machining. That’s why 7075 aluminum is more challenging to machine.

In contrast, 6061 aluminum can be easily cut, milled, drilled, and cast, exhibiting better machinability than 7075 aluminum due to its moderate strength, ductility, and lower cutting forces during machining. As a result, 6061 aluminum alloy stands as the go-to choice for numerous machined components, as it harmoniously blends machinability with strength and other desirable properties.

Chemical Characteristics

Here we mainly focus on corrosion resistance and anodizing to check the difference of their chemical characteristics.

Corrosion Resistance

6061 aluminum alloy has significantly better corrosion resistance compared to 7075. This is because 6061 contains magnesium and silicon, and has a lower copper content. The precipitates formed by magnesium and silicon in the aluminum matrix, such as Mg2Si, do not significantly reduce the alloy's corrosion resistance. On the contrary, the uniform distribution of these precipitates helps prevent localized corrosion. In contrast, the high content of zinc and copper in 7075 aluminum alloy forms corrosion-prone precipitates such as Al2CuMg and MgZn2. These precipitates lead to localized galvanic cells, making the alloy more susceptible to corrosion when exposed to moist or corrosive environments. Additionally, the presence of copper further promotes pitting and crevice corrosion.

Anodizing

Anodizing is an electrolytic passivation process that increases the thickness of the natural oxide layer on the surface of aluminum and its alloys. This process enhances corrosion resistance, wear resistance, and the ability to accept dyes or other coatings.

Both 6061 and 7075 aluminum alloys can be successfully anodized to get improved corrosion resistance and surface properties. 6061 aluminum, with its more uniform microstructure, is easier to anodize, forming a uniform, dense, and strongly adherent oxide layer. On the other hand, due to the high zinc and copper content, anodizing 7075 aluminum tends to produce an oxide layer with uneven thickness and many local pores. The oxide layer on 7075 also tends to have weaker adhesion to the substrate, making it prone to peeling or cracking.Therefore, anodizing 7075 aluminum may require stricter quality control measures and higher costs to ensure a uniform and defect-free oxide layer.

Weldbility

6061 aluminum is known for its excellent weldability. Its moderate strength and good resistance to cracking during welding contribute to its overall weldability. This alloy can be welded using various methods, including gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and resistance welding.

Although 7075 aluminum alloy is also weldable, it poses more challenges compared to 6061 aluminum. The alloy's high strength and hardness can lead to increased stress and cracking in the welded joints. Additionally, since the melting point of zinc is much lower than that of aluminum, zinc will melt before aluminum during the welding process. The early melting and volatilization of zinc will result in the formation of zinc-rich phases in the welding area, which are prone to porosity and cracking during the welding process, thereby reducing the welding quality. If 7075 aluminum parts need to be connected, they can only be connected with rivets or other fasteners.

Cost

In general, 7075 aluminum tends to be more expensive than 6061 aluminum. Primarily, 7075 contains a higher proportion of zinc and copper, which are more costly, leading to higher raw material costs. Additionally, the processability of 7075 aluminum alloy is relatively poor, particularly during cutting and welding processes, which require higher technological demands and costs. Moreover, the high hardness and strength of 7075 result in faster tool wear and longer processing times, thereby increasing manufacturing costs.

6061 vs. 7075 Aluminum: Which One Is Better for Your Application?

Until now, we have an overall understanding of the differences between 6061 and 7075 aluminum alloys. Both of them have excellent mechanical properties and are widely used. But regarding your application, which one is more suitable? The selection primarily depends on specific usage environments, performance requirements, and cost considerations. We summarized pieces of advice as below to help you make informed decisions.

1. Generally, 6061 aluminum alloy can be as the primal choice. Because it is more cost-effective, and its good processability and weldability make it easier to work with. Despite its medium strength, 6061 aluminum can reach the requirements for a wide range of applications in construction, transportation, and electronics.

2. When your products are used in marine environments, it’s better to choose 6061 aluminum. This is not merely about 6061’s higher corrosion resistance than 7075, but a concern of economical suitability about the selected alloy. Although through proper surface treatments, both alloys possess outstanding corrosion resistance, 7075 aluminum used in such conditions seems wasting its potential for other demanding usages

3. In the following situations, 7075 aluminum is more effective to achieve the functions of your application.

• Cost is not a primary concern.
• Higher strength and hardness are required. This mainly applies to fields such as aerospace, military, and high-end automotive manufacturing.
• Your products will be used under long-term cyclic loading. Because 7075 aluminum’s good fatigue resistance can maintain stable performance under such circumstances.

Conclusion

Aluminum alloys are among the most widely used metals for manufacturing processes. However, with the wide variety of aluminum alloys available, it would be confusing to choose the right one for your project. As one of the largest ISO 9001-certified manufacturers specializing in custom hardware parts in China, our experts can assist you in the material selection process. If you are looking for CNC machining services or aluminum extrusion services for your 6061 or 7075 aluminum project, please feel free to contact us.