I believe it is the Eclipse 500/550 that uses friction stir welding for some form of construction technique, I vaguely remember a youtube video detailing how it’s done.
FSW is a good process. Mostly developed by the UK Welding Institute. As the temperature is only raised to the transition level used in extrusion, there is less of a heat affected zone than in MIG welding. The joint has good integrity and can form a continuous water tight joint. But the weld zone loses mechanical strength unless it is re-heat-treated. This isn’t always a problem as the joining area is greater than a rivet line.
Spot welding of aluminium alloys is getting greater use in the automotive industry, though that may not be suitable for aerospace for a few reasons.
Silvaire – actually the gold coloured rivets, if they are of the AN460AD-xx variety are uncoated. The colour is due to the copper content of the rivet alloy. It’s actually the silver coloured ones that have a galvanic coating, though they seem to be used interchangeably.
Thanks for the clarification on AN rivet coating – that makes sense! 
Socata did quite a bit of spotwelding on their Rallye aircraft. Not funny with corrosion / repairs.
Sometimes it is corrosion, but sometimes when the paint bubble is removed, there is nothing there. The paint seems to have just decided to bubble up.
The paint will not bubble of for no reason, so some chemical activity is going on in there. Have you checked the other side of the rivet?
The underside is the fuel tank, so not much chance of corrosion I would hope.
I just take the paint off, plus about 2mm around the rivet, and put a drop of epoxy primer on it…
Curiously the paint on my Jetprop is starting to fail predominantly around the rivet heads after 14 years.
The acknowledged PA46 guru in Germany examined my aircraft a few years ago as I wanted to confirm they were not working rivets, and he told me that Piper used a harder paint formulation around the time mine was built, and it is quite common to see this type of paint failure in my generation of airframe.
I would suspect that the different material characteristics if the rivets are a factor. Mine is an Imron paint.
For the first few years of ownership in Thailand the aircaft was parked outside uncovered, which cannot have helped given the brutal UV and heat/humidity out here. :-(
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