As a general purpose aluminum, 6061 combines good machinability, strength, and weldability. It can additionally be anodized with a good finish. We use it for many of the machined components in the Mark X.
7075 Aluminum is one of the strongest aluminum alloys. With good fatigue strength and a high strength-to-weight ratio, this alloy is stronger than common structural steels (A36, 1018). We use it on the kinematic coupling in the bed of the Mark X. It’s also common in aerospace and automotive racing.