When an object has zero acceleration, it means that the net force acting on the object is zero. According to Newton's second law of motion, when the net force on an object is zero, the object will either remain at rest or move with a constant velocity.
If an object is already in motion and experiences zero acceleration, it will continue to move at the same velocity it had before the acceleration became zero. This constant velocity can be considered as the maximum velocity attainable under the given circumstances.
However, it's important to note that this maximum velocity is specific to the absence of external forces. If external forces, such as friction or propulsion, act on the object, they can alter its velocity. In the absence of such forces, an object with zero acceleration will have a constant velocity, but it may not necessarily be the maximum velocity it can achieve in the presence of external forces.