How can I ensure low-resistance ground contacts to an aluminum enclosure?
I am going to elaborate a bit so this becomes an answer.

Typical avionic equipment has a typical bonding requirement of 2.5 to 5\$m\Omega\$ around a chassis. There are different classes of bonding and earthing with their own set of requirements, depending on the threat and application.

There is an excellent survey from NASA on methods used over the years and the rationale behind them.

As already noted, MIL-HDBK-419A Volume 1 and Volume 2 contain a wealth of application assistance.

On the subject of oxidisation, it is common to use a chemical conversion coating to prevent aluminium from oxidising in both aircraft and on board ships; this has an advantage of reducing overall corrosion artefacts as a mated face could be the same metal as the new coating.

Note that galvanic corrosion (also known as dissimilar metal corrosion) can be a major issue in aircraft, and we seek to minimise (or eliminate) it as it adds costs to the system operator because galvanic corrosion will eventually require repairs.

It is not always apparent that a great deal of assistance can be available for this type of issue, unless you just happen to be in (or have been in) one of the industries that require it.