Scales is Aberdeen's second signing in two days following the capture of right-back Jayden Richardson from Nottingham Forest on a three-year deal.

"He's a strong character with a winning mentality," Aberdeen manager Jim Goodwin said of Scales.

Richardson arrived from Nottingham Forest for an undisclosed fee, a day after fellow right-back Calvin Ramsay left for Liverpool in a £4.2m move.

The 21-year-old played 23 times on loan at Notts County last term and has signed a three-year contract at Pittodrie.

"The opportunity for young players to come to Scotland and make an impact is clear to see," Nottingham-born Richardson told Aberdeen's website.

"Playing in front of big crowds is something all players aspire to."

Richardson has also had loan spells at Exeter City and Forest Green Rovers and Dons manager Goodwin added: "He is a very quick, dynamic and attacking full-back who, I am sure, will use this as a platform to go and prove himself."