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Most launch vehicles use aluminum alloy AA2219 for LOX propellant tanks, has anyone used AA6061 with additional coating instead?

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    $\begingroup$ The claim that most vehicles use 2219 aluminum certainly needs some support, since numerous launch vehicles use composites, aluminum-lithium alloys, or stainless steel...and is there some reason you are interested in 6061 aluminum in particular? Also, the question seems to make the assumption that the choice of aluminum alloy has something to do with a required coating? $\endgroup$ Dec 2, 2021 at 17:41
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    $\begingroup$ Original shuttle tank was 2219 but the super lightweight tank used late in the program was an aluminum-lithium alloy called "weldalite" if memory serves. Some of the LH2 tank was still 2219. $\endgroup$ Dec 2, 2021 at 19:03

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The tensile strength of A2219 is 172–476 MPa, of A6061 only 124–290 MPa. A2219 contains 5.8 to 6.8 % copper, A6061 only 0.15 - 0.40 %. The galvanic series voltage of copper is +0.52 V, of aluminum -1.66 V. Due to the large potential difference and the high concentration of copper the A2219 alloy is less corrosion resistant.

To compensate for the lower corrosion resistance, 2219 aluminium can be clad in a commercially pure alloy such as 1050 or painted.

A6061 is more resistant to corrosion and may be used even for boats used in salt water. A6061 does not need coatings that much like A2219.

The Space Shuttle Standard Weight Tank was fabricated from the 2219 alloy. The Columbus module on the International Space Station also used 2219 aluminum alloy.

For space applications A2219 is particularly suitable due to the higher tensile strength allowing lighter parts.

A fine powder of aluminum metal reacts explosively on contact with liquid oxygen; under normal conditions, however, aluminum forms a thin oxide layer (~5 nm at room temperature) that protects the metal from further corrosion by oxygen.

Aluminum alloys are highly susceptible to ignition and combustion in oxygen, but because of their lightweight, designers are tempted to use aluminum in spite of the ignition hazards. An anodizing surface preparation should be used for aluminum parts subject to conditions that may generate particulate or be subjected to particle impacts.

See SAFETY STANDARD FOR OXYGEN AND OXYGEN SYSTEMS

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