CAn't find anything exact. But based on the binning/specs I would assume
Micron D9JNM
The PCB does not appear to be as robust on the Pi series, so not sure how high voltage will effect them. But it is the same ICs I have on my patriot ELK kit, I have run up to almost 1800 7-7-7 with 1.85 volts and I just juiced it to 1.9 to get 2100+ at 9-9-9 Probably did not need that much though
I overvolt since they stay real cool anyway and I have not had enough time on this rig to really work out the ideal voltages for every setting. I do know that I have crashed on more than one occasion because of not enough Vdimm so I just set it a little high to start with.
Also if your board lets you set MCH strap, these things just LOVE tight timings