Thanks to everybody for all the concern. I'll practice my aluminum welding and fix it properly. These are the spare set of rims and tires and are not on the truck.
At the rare risk of sounding like a know it all, one more important point. From the little you showed, that has the earmarks of a fatigue failure, not ground impact damage. Fatigue cracks are the result of casting defects. The vibration and the stress on the piece eventually causes the defect to appear in the form of a crack.
Here’s the bad news. The assumption that it will just continue to crack is a false assumption. Fatigue cracks are usually catastrophic failures. If it’s something the size of a dime it’s annoying. If it’s something the size of that wheel with a big tire on it it’s going to be instantaneous and violent. I don’t know the percentage chance that it will fail, but if it fails, the possibility of a catastrophic failure, pieces instantly flying apart, is actually likely.
As regards welding it up, there are all kinds of things about welding temperature, what alloy, and how the thing is cooled weather it just cools down, you call it with oil or you quick cool with water, etc. If you weld it to look perfect, but you affect the casting, you could actually create a bigger hazard, even though it looks prettier. If your time is worth a few bucks an hour, for the same amount of money, you can hunt around and find a decent wheel.
That’s the last of my two cents, but it’s a good two Cents.