In my experience as a tea drinker in the U.S., second infusion is the most common spoken usage of infusion in the context of steeping tea leaves or brewing tea. The initial act of pouring hot water over tea leaves is usually called "making a pot/cup of tea" or "brewing a pot/cup of tea." It would sound stilted and pedantic to say "I'll prepare a tea infusion" or something like that. I've never heard anyone say "first infusion" for initially brewing a pot of tea, presumably because there's no reason to differentiate the "first" one when it's usually the only one.
As another variant, some people use a tea infuser for steeping loose leaf tea so as to make it easy to remove the leaves from the water once the tea has steeped (or brewed or infused) for a sufficiently long period of time and/or to keep the leaves in the pot when the tea is poured into a cup.
A Google ngram viewer search suggests that "make tea" is the most common in written English, but variants with "brew" or "infusion" occur also in both British and American English (though I might have missed other common tea-brewing-related phrases).