A combination of elements making Scott's hero abandon his lake (5)

'a combination of elements' is the definition.
(alloy of iron and nickel)

'scott's hero abandon his lake' is the wordplay.
'scott's hero' becomes 'Lochinvar' (hero in Walter Scott's poem Marmion).
'abandon his' indicates named letters should be taken away.
'lake' becomes 'loch' (loch is a kind of lake).
'lochinvar' with 'loch' removed is 'INVAR'.

'making' is the link.