The key differences between aluminum 6061 and 6063 for CNC machining prototypes are as follows:

Strength and Hardness:
Aluminum 6061 has a higher tensile strength (310 MPa) compared to 6063 (260 MPa), making it more suitable for applications requiring greater structural integrity.
6061 also has a higher hardness, which allows for better machinability and the ability to hold tighter tolerances.

Corrosion Resistance:
6061 aluminum offers superior corrosion resistance, particularly in marine and outdoor environments, due to its enhanced alloying elements.
6063 has a slightly lower corrosion resistance, but is still suitable for many applications.

Machinability:
6061 aluminum is generally considered to have better overall machinability, allowing for higher cutting speeds, feed rates, and better surface finishes during CNC machining.
6063 is still relatively easy to machine, but may require slightly slower cutting parameters to achieve the desired results.

Applications:
6061 is widely used in aerospace, automotive, and industrial applications where higher strength and durability are required.
6063 is more commonly used for architectural applications, such as window frames and door handles, where appearance and finishing are more important than ultimate strength.

For CNC machining prototypes, the choice between 6061 and 6063 will depend on the specific requirements of the project. If the prototype needs to closely mimic the properties of the final production part, then 6061 would likely be the better choice. However, if the focus is more on aesthetics and finishing, 6063 may be a suitable alternative, offering a good balance of machinability and cost-effectiveness.

Ultimately, working with an experienced CNC machining provider like Metalstar can help you determine the most appropriate aluminum alloy for your prototype based on your unique design and performance requirements.