Those shards you recovered can only have come from one place, Malykriss. It's the seat of the Lich King's metalworking operations, to the east of Corp'rethar.
What's puzzling is that metal isn't needed to stitch together abominations or flesh giants, or to summon skeletal servants. Find the skeletal runesmiths working on the bottom level of Malykriss and capture the plates they're working on. We need to find out why this metal is finding its way to the Fleshwerks.
These plates match the shards almost exactly. They must be using cuttings from them to "enhance" the ghouls produced here. The Scourge is desperate enough to make a weapon of anything, it seems. All the more reason to hasten our destruction of this abominable place!