The AK74 muzzle device is a brake and compensator. It's retained by 24x1.5mm RH thread and a plunger, the interior is hardchromed to resist erosion from gas wash and corrosion.
The AK, with its dropped stock, has always had pretty bad muzzle climb on full auto. 5.45x39 has less recoil but the Sov Army wanted to make full auto fire (which they do more often than aimed semi-auto) more effective.
BSW