If I get married to my fiancé after we both finish AIT and are on leave, will we get stationed together after getting to our duty stations?

You'll both have your orders long before you get married. HRC isn't going to change your orders once they're cut even if you're married

After you are married, you have to enroll in MACP, then request same assignments.
https://www.hrc.army.mil/content/Married%20Army%20Couples%20Program

Short answer: No.

Long answer: FIRST you have to get married. THEN you can apply for MACP (Married Army Couple's Program). Once you are BOTH fully enrolled, THEN you can work on being stationed together.

You will probably both PCS to the same NEXT duty station, at different times, as slots come available. After that, you should be able to PCS together.

But these are "probably" and "should," because the needs of the Army come first. MACP is a program for the Army to TRY to station couples together. It is NOT a guarantee or a requirement.