Need Help to stop child from hitting me

Has anyone had luck with stopping their adopted child from hitting them? My adopted son is almost 5 years old and has been with us for almost 1 1/2 years. He hits me (Mom) when he gets mad. I have tried everything from ignoring it to timeouts and nothing has worked. He feels like he can do it and shows no remorse for the fact that he punches Mommy. Any thoughts? Thanks, Julie