The engineers at e*thirteen carefully select materials for every product we make, and the most common material we use is aluminum. In engineering applications, aluminum is almost always alloyed with other elements to improve the mechanical and other properties of the base aluminum, such as strength, fatigue resistance, corrosion resistance, finish-ability, and others.

Aluminum alloys are designated by a 4 digit number followed by additional information after a dash mark. The first digit designates the primary alloying agent; for instance, 6XXX = Magnesium. (To read all about this, check out the Wikipedia Article Here.) Therefore aluminum alloys can be grouped into families according to this primary alloying agent.

The three aluminum alloys we use the most are 6061-T6, 6069-T6, 7075-T6, and 7050-T7. (We occasionally use other aluminum alloys, such 6066-T6 and 2024-T6, for specific applications.)  These materials are essential for producing high-quality, durable components for various products.

A note about engineering materials from the engineers: while the material used for a product is moderately interesting, it's only part of the story. How much material is used, how it is processed and finished, where you put the material in the part, and many other factors must be considered as part of a great design! It's never as simple as "7 is greater than 6, therefore it's better." 

Let's dive into these materials and discuss their pros and cons.

6061-T6 Aluminum

6061-T6 is the workhorse aluminum alloy, widely used in various industries due to its versatility and affordability. 6061-T6 includes alloying elements magnesium and silicon, balancing strength, corrosion resistance, and weldability. 

Pros:

• Cost-effective: It's relatively inexpensive compared to other aluminum grades, making it a popular choice for manufacturers.
• Corrosion resistance: 6061-T6 offers good protection against environmental factors such as moisture and oxidation, ensuring a longer lifespan for components.
• Weldability: This material is easy to weld, which makes it suitable for constructing bicycle frames and other components requiring welding.
• Anodizing: 6061-T6 is relatively easy to anodize, producing consistent and attractive color finishes.

Cons:

• Lower strength: Compared to other aluminum alloys like 6066/6069, 7075, 7050, and 2024, 6061-T6 has lower strength, which may not be ideal for high-stress applications, or may result in a heavier finished product.

Common Applications:

• Hub shells and Rims
• Stems and Handlebars
• Pedal Bodies
• Seatpost components
• Crank Arms

6069-T6 Aluminum

6069-T6 is an improved version of 6061-T6, providing better strength and fatigue resistance without compromising corrosion resistance or weldability. Similar to 6061-T6, it contains magnesium and silicon but in slightly different proportions.

Pros:

• Higher strength: This alloy offers higher strength than 6061-T6, making it suitable for more demanding applications.
• Fatigue resistance: 6069-T6 performs well under repeated stress cycles, making it ideal for mountain bike components that experience constant impacts and vibrations.
• Corrosion resistance and weldability: It maintains the same corrosion resistance and weldability properties as 6061-T6, ensuring durability and ease of manufacturing.
• Anodizing: 6069-T6 is also easy to anodize, providing good color consistency and finish quality similar to 6061-T6.

Cons:

• Slightly higher cost: Due to its improved properties, 6069-T6 is slightly more expensive than 6061-T6, and may be less readily available.

Common Applications:

• Welded Aluminum Rims
• Stems
• Crank Arms

7075-T6 Aluminum

7075-T6 is a high-strength aluminum alloy primarily used in aerospace and military applications. It is known for its excellent strength-to-weight ratio and superior fatigue resistance.

Pros:

• Exceptional strength: This alloy offers the highest strength among most aluminum alloys, making it suitable for components that require exceptional durability and resistance to deformation.
• Excellent fatigue resistance: 7075-T6 withstands repeated stress cycles, ensuring long-lasting performance in demanding applications.
• Lightweight: Its strength-to-weight ratio is impressive, resulting in lightweight components that don't compromise performance.

Cons:

• Poor corrosion resistance: Compared to 6061-T6 and 6069-T6, 7075-T6 has lower corrosion resistance, which may require additional surface treatments to protect against environmental factors.
• Anodizing: 7075-T6 can be anodized, but it may require more attention to process control, and the color consistency might be less uniform compared to 6000 series aluminum.
• Limited weldability: This alloy is more challenging to weld, which can limit its applications in components that require welding.
• Higher cost: Due to its high strength and specialized applications, 7075-T6 is more expensive than the other alloys.

Common Applications:

• Cassette Sprockets and Chainrings
• Chainguide Backplates 

7050-T7 Aluminum

7050-T7 is a high-strength aluminum alloy containing zinc, magnesium, and copper. It was developed to offer improved properties over 7075-T6, particularly in terms of stress corrosion cracking and fracture toughness.

Pros:

• High strength: 7050-T7 offers comparable strength to 7075-T6, making it suitable for high-stress applications.
• Improved stress corrosion cracking resistance: This alloy provides better resistance to stress corrosion cracking than 7075-T6, enhancing its durability in challenging environments.
• Enhanced fracture toughness: 7050-T7 exhibits superior fracture toughness compared to 7075-T6, which is advantageous in applications where resistance to crack propagation is critical.

Cons:

• Higher cost: Due to its improved properties and specialized applications, 7050-T7 is generally more expensive than 7075-T6.
• Anodizing: 7050-T7 can be anodized, but it may require more attention to process control, and the color consistency might be less uniform compared to 6000 series aluminum.
• Limited weldability: Similar to 7075-T6, this alloy is challenging to weld and may not be suitable for applications requiring welding.

Common Applications:

• Crank arms and Aluminum Crank Spindles
• Stems and Handlebars

In summary, each aluminum grade has its unique set of properties, offering different advantages and disadvantages for various applications. 6061-T6 is a cost-effective option with good corrosion resistance, weldability, and ease of anodizing, but lower strength. 6069-T6 balances strength, fatigue resistance, corrosion resistance, weldability, and ease of anodizing. 7075-T6 offers the highest strength and fatigue resistance but with lower corrosion resistance, limited weldability, more challenging anodizing, and a higher cost. 7050-T7 improves certain aspects of 7075-T6 performance.