Personally, I find Aluminum trivial to solder with regular Sn60/Pb40 solder, provided you can get enough heat into it. With a 100W Weller soldering gun its only a little harder than soldering to tarnished copper. With a wimpy little long conical bit on a low powered iron you wouldn't have a snowflake's chance in hell of getting aluminum to wet with solder. Don't use your best bit as you have to rub the aluminum surface through the solder pool with moderate pressure, and that can be hard on the bit plating. However unlike other aluminum soldering techniques like working under pools of oil and aggressive specialist fluxes, it doesn't immediately mess up your bit, and no special cleanup is required.
What I do is prepare the aluminum surface by abrading with a fibreglass pencil, then I immediately apply liquid rosin R flux* and continue abrading it through the flux pool, which excludes most of the oxygen in the air. Before the flux has fully dried out, I tin the desired area by forming a small solder pool and rubbing the surface under it with the bit, (to disrupt the very thin oxide layer that will have reformed because the flux failed to totally exclude all oxygen), till it starts to wet, then expanding the wetted area by working outwards adding fresh solder as I do. The solder slightly dissolves the aluminum, so the oxide at the edge of the pool is undercut and its easy to get the tinned area to expand. I then wipe off the excess solder while still molten, and clean up excess flux with IPA leaving me a tinned area that can be soldered to normally.
You don't get the feedback of the solder freely wetting the metal surface that you get with copper alloys when they reach a high enough temperature, so judging if your iron is adequate and technique good enough takes practice.
If you practice on thin aluminum sheet, you know you've got there when you can bend the sheet across the tinned patch without any signs whatsoever of it lifting at its edges. Once you've mastered tinning aluminum, getting nice joints to tinned aluminum without preheating takes a bit more practice, as the aluminum conducts heat away so fast its easy to get a 'cold' joint.
Here's one I just did to demonstrate on an aluminum coupon cut from a foil takeaway container. I haven't cleaned up the flux residue from the final stage of soldering a wire onto the tinned patch, so it doesn't look as pretty as it should. It took longer to get a decent closeup photo than it did to do, including surface preparation, and even longer to type up this post!
* I generally use liquid R flux not RMA or RA, and not a paste or gel flux because used sparingly it can be treated as no-clean, so when working with aluminum, its just what I've got handy on my bench. Any other high solids general purpose liquid flux would work equally well for aluminum, as long as it forms a tenacious liquid film to protect the aluminum round the edges of the solder puddle from rapid oxidisation.