I believe what it does is refine the grain structure of the metal and it also aligns the polarity thus strenthening the part. This would be beneficial to a casting.
That’s about what we were told. I was offer this service back in the late 1970’s early 1980’s for free. My buddy worked at a local machine shop that offered it. I didn’t know anything about it and didn’t want to risk getting him in trouble. My hometown was a hotbed for industrial machine shops.
