U.S. auto parts maker TRW Automotive Holdings Corp said it would be bought by German peer ZF Friedrichshafen for $13.5 billion, including debt, creating a global automotive supply powerhouse.ZF's offer of $105.60 per share in cash represents a premium of 1.7 percent to TRW's closing price of $103.85 on Friday.ZF, a major provider of steering systems and powertrains, would get a leading maker of automotive safety products, such as brakes and air bags, Reuters had reported earlier.