Welding alloy (6)
I believe the answer is:
solder
'welding alloy' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for solder that I've seen before include "Metal bond" , "Alloy melted to join circuit components" , "Fusible jointing alloy" , "Join two metal surfaces, using an alloy" , "Join two metal surfaces together" .)