Well, the rumors and speculation on whether the Galaxy S5 will have a metal body are once again making their presence felt, through separate reports published by the ever-alert media. First up is a report by ETNews, which says that Samsung has begun testing a “diamond metal surface treatment technology” for metal cases – basically, a phone's metal case is coated with a diamond-like material, making it more resistant to scratches and deformation. This diamond-like material is obtained by exposing carbon to high temperature and high pressure, and is then turned into liquid or powder and applied to a metal case.
But will this technology be ready in time for the Galaxy S5? Maybe it will, maybe it won't, but according to a report by DigiTimes, the Galaxy S5 won't have a metal body at all. Taiwan-based chassis makers have commented that rumors of Samsung adopting metal-alloy chassis for the Galaxy S5 and starting production on them are unlikely to be true, as no company has yet begun to mass produce these chassis. Furthermore, DigiTimes‘ sources believe Samsung doesn't really need metal chassis as they've already become mighty successful selling plastic-based devices (a sentiment that many will agree with, because frankly, most of those millions of folks buying Samsung devices aren't exactly complaining about the lack of a more premium feel).
Basically, at this point it is totally uncertain whether we'll actually see the Galaxy S5 have a metallic body. Most rumors suggest we will, but considering every Galaxy S flagship is preceded by rumor-mongering of all sorts, it's best not to take any of those seriously, especially since Samsung does a nifty job of hiding all details on its flagships' design.