Originally Posted by Badzilla

Bull. Aluminum is strong, extremely reliable, and lightweight, that's why it's used extensively in aviation and even aerospace.

The Apollo Command Model was made of an aluminum honeycomb-sandwich bonded between sheets of aluminum alloy.

Lockheed Martin has chosen an aluminum-lithium alloy for the primary structures of NASA’s new Orion spacecraft.

Ever since the launch of Sputnik a half-century ago, aluminum has been the material of choice for space structures of all types. Chosen for its light weight and its ability to withstand the stresses that occur during launch and operation in space, aluminum has been used on Apollo spacecraft, the Skylab, the space shuttles and the International Space Station. Aluminum alloys consistently exceed other metals in such areas as mechanical stability, dampening, thermal management and reduced weight.

The problem is cost. Cromoly is cheap compared to good aluminum. I can't even find 7075 aluminum tubes from retail outlets online (it can be ordered if you can afford a minimum quantity). Some 2024 is available retail, it's stronger than 6061 but not strong as 7075.