As a matter of general principle, the second noun in a combination like 'key card' describes the nature of the object. Thus, a key card is a card that works/look/functions, etc. as a key, whereas a 'card key' would be a key that works/look/functions, etc. as a card. In your case, I have seen and heard of cards that function as keys (e.g. in hotels) but I have no idea what a 'card key' would be.
A keycard lock is a lock operated by a keycard, a flat, rectangular plastic card with identical ... RFID proximity cards. Keycards are frequently used in hotels as an alternative to mechanical keys. The first commercial use of key cards was to raise and lower the gate at automated parking lots where users paid a monthly fee.