The Lionchief USRA 0-8-0 is an "entry-level" model, and much of it is plastic, but not all. Lionel does make a "premium" 0-8-0 that is all zinc, including the tender. It is heavier. Larger motor; more features; probably thicker die-cast sub-assemblies. The two locos represent the same prototype, but the tooling is not shared. The premium model is better-detailed, but the Lionchief is not bad on that score.
The Williams loco is all die-cast. Its tender is plastic.
(Your English is just fine, by the way. Better than some natives that I know.)