If I were to split a sword in two, and use a different infusions on both parts, and lock them back together (without fusing them together), would I get one weapon with 2 artificer infusions?
Only one infusion per object
The rules in Tasha's Cauldron of Everything (where the Artificer is introduced) say on page 13 (emphasis mine):
You must touch each of the objects, and each of your infusions can be in only one object at a time. Moreover, no object can bear more than one of your infusions at a time.
It also goes on to say what happens if you try what you described:
If you try to exceed your maximum number of infusions, the oldest infusion ends, and then the new infusion applies.
Note that it doesn't specifiy that this is what happens if you try to infuse the same object twice - it just says that this is what happens if you try to exceed the maximum (by whatever means).
So either you "combined" the two parts of the sword in a way that still leaves them as two objects. in which case you would attempt to hold two objects (weapons) in one hand (which doesn't work), or you combined them in such a way that it becomes a single object, in which case the older of the two infusions stops and the newer remains.