While some may have a small amount of aluminum it would not be near enough to call it an aluminum alloy. They call the alloy babbit. Perhaps the shells are aluminum, but the bearing surface is babbit.

Note that automotive bearings are constanty fed oil under pressure, the pressure prevents actual metal to metal contact. The soft babbit material asorbs hard debris that get past the oil filter so the soft material is ideal for pressure fed lubrication systems. For our engines the oil is not pressure fed and there is a lot of metal to metal contact so a harder metal (but not too hard) is prefered.