This came up in our last session. My pact of the blade warlock summoned a longsword to fight a grey ooze. Any nonmagical metal or wood that touches an ooze is corroded. According to the PHB, The pact weapon is magical for the purposes of immunities and damage resistance. So it was unclear to my group whether or not my pact weapon would be corroded when touching the ooze.
The DM ruled that the pact weapon isn't actually metal, but some kind of magical force, so we were ok. But I was interested if anyone else has run into this.