Right-back Melhado has only made one single appearance for The Ammies in the cup last season.
He has strong football league experience as he started in the Wolvehampton Wanderers academy and joined League one side Burton Albion. Sargent, who joined Salford from Wrexham last season, is very versatile, playing anywhere in the midfield.
The 20-year-old has featured three times for the League Two side, including in the EFL Trophy against Leicester under-21s.
Both players will be able to feature in the matchday squad for Saturday’s home game to 11th placed Lancaster City.
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