I believe you're a bit confused on a few points, friend.
You're talking about "soldering." The soldering wire you used contains no aluminum whatsoever. It was probably an alloy of tin + antimony, or tin + bismuth + silver.
"welding" is done with a filler metal that has a melting point the same or nearly the same as the parts to be joined.
"soldering" is done with a filler metal that has a much lower melting point than the parts to be Joined.
Whether it will hold depends on the quality of the soldering job, the cleanliness of the joint beforehand, and type of solder used.
General-purpose plumbing solders don't always work well for radiators, because the constant changes in temperature and pressure require a stronger, more mechanically stable alloy. You should use a solder alloy specifically intended for radiator repairs.