Wishbones used to be made of steel, constructed by welding a mix of tubular (round or aero profile), machined and fabricated sections. Tyrrell did run a CNC machined aluminium rear top wishbone back in the early eighties.
Teams have run welded Ti wishbones too; this has been mainly for thermal reasons such as the element being in the line of the exhaust plume. Although Renault did switch to a rear Ti wishbone after a failure of a CFRP wishbone at Silverstone.
By the nineties teams were wrapping the wishbones and pushrods in carbon fibre, partly for aerodynamic reasons and partly for stiffness increases, especially with the pushrod.
The natural progression was to create a hybrid element made from carbon fibre sections and Titanium end fittings, the joint being both bonded and mechanically fastened. Development was rapid in this area and teams soon found it was best for QA/NDT reasons to have the Ti end fitting inserted into carbon section.
Jordan were probably the first team to run a completely carbon suspension element, that is the flexure and leg of the suspension element made from as a monolithic structure.
Although teams still have smaller metallic fixings inside the wishbone for mounting hardpoints and often the entire outboard end is still a CNC machined Ti part. But this tends to be only for the higher loaded wishbone, i.e. Front bottom wishbone outer ends.
Construction of the carbon fibre ‘leg’ sections has developed since the nineties too. From two part mouldings bonded together or monolithic parts from a closed mould using air bags to consolidate the plies. Nowadays I understand the closed mould approach is still used, but the pressure comes from a slightly oversized rohacell core, which applies pressure to the plies when the mould is closed.
Although the shift to CFRP has improved stiffness, its more lightness that’s the benefit of a material change. These stats from a F1 source reinforce this fact.
Carbon with steel ends ~50%
All carbon ~40%
There are other benefits, although in F1 terms a CFRP wishbone does not have a lifing problem (i.e they only have to last 1 season), as the part does not suffer from fatigue like a metallic part will. Additionally using flexures on CFRP wishbones reduces the cost of the spherical bearings teams will work through over the course of a season.
Of course the offset of these benefits are many fold and are the reason other formulae do not use CFRP suspension elements. Firstly cost the tooling will cost tens of thousands of pounds for each wishbone. Make the wishbones unique to each corner and that’s eight sets of wishbone tooling, plus the pushrods\trackrods. Any dimensional change over the season will force a new set of tooling to be made.
Then the QA issues are immense. Although the CFRP element will not fatigue, any damage or overstressing of the part will render it useless. Teams conduct exhaustive NDT to each wishbone: i.e. stress tests, acoustic measurement, Ultrasound. This takes time and resources.
I’ve a load of this info and a bit about flexures to put on my blog over the winter.