Tesla has switched their newer lines to casting. It seems like it's mostly about manufacturing efficiency rather than strength -- they can cast the whole underbody of the vehicle as a single piece rather than having dozens of stamped pieces that need to be welded or riveted together. Initially they were doing the front half as one piece and the back half as another, but they've needed to get bigger and bigger (higher- and higher-force) machines as they've gone from two-piece to single-piece construction.
