What's the current thinking on aluminium and titanium and preventing bimetallic corrosion? PTFE tape? Grease of some description? Thread lock? I imagine that copper slip would be entertaining and expensive with almost visible changes.

Galvanic corrosion is prevented in the aerospace industry using many different methods ranging from assembling using wet epoxide primer to crazy zinc pastes. Basically anything inert which will separate the two materials. It really depends on whether you need to disassemble or not. Moly grease will do it too dependent on your application.

Its for installing an aluminium BB into a Ti frame.

So copper slip isn't the way to go then?

I don't have much experience with copper slip tbh but a good molybdenum grease will definately do the job.

I didn't think Ti/Al would be all that reactive?

Ti/Al does – I had a Record BB almost complete corrode away within 18 months.

Copperslip.

Oh it does! Ignore it at your peril.

I'm sure that someone showed a BB they'd fitted into a Ti frame with copperslip – the threads had pretty much disappeared.

We used to have some special grease for steel fixings on alu greenhouses – I seem to remember it's green. But it's also probably from the 1950s or 60s, so it'll most likely be banned by now.

I've used copperslip on Ti/Al parts for years on MTB & off road motorcycles, never had a problem. Magic stuff.

Loctite 222

PTFE tape might be the way to go.

MoS2 or nickel based anti-seize.

CoppaSlip is for Ti/Ti interfaces.
I've always used anti-seize on Ti/Al or Ti/steel with no problems so far (he says, remembering that he hasn't removed the BB from the Ti hardtail in a good few years!)

Specific carbon grease if you're using a carbon interface anywhere.

If a metal has a different "reactivity" to another and touches it, corrosion will happen. The greater the "gap" in reactivity, the faster the corrosion.

I'd be tempted to use Alumslip or Polyslip (same manufacturer) over Copaslip.

I've just installed my BB on my Ti build with FinishLine Teflon grease. Never gave it a thought to be honest til reading this thread. Should I take it out now and again to check for corrosion?

What you need is a sacricial metal

Shove some magnesium down the seattube

Or sacrificial?!

Works in fluids, doesn't work in air.

Anything that physically keeps the two metals apart will work to a greater or lesser degree. The bonus with moly and teflon grease and also copaslip is that they have particles in suspension which help keep the 2 metals apart. If galvanic corrosion can occur then sacrificial protection can work as they work on exactly the same principles. A bit extreme though bolting a block of zinc to your frame 😀

Loctite threadlocker can act as a sealant (to prevent the ingress of water into the threads) and as an antiseize (to help prevent galling and galvanic corrosion of the threads).