According to Wikipedia,
Abstraction: Abstraction in mathematics is the process of extracting the underlying essence of a mathematical concept, removing any dependence on real world objects with which it might originally have been connected, and generalizing it so that it has wider applications or matching among other abstract descriptions of equivalent phenomena
Generalization: A generalization is the formulation of general concepts from specific instances by abstracting common properties.
I can think of abstraction without generalization, in the case where there is only one or same number of objects even if you go higher up the abstraction. e.g. if there is only one human and that human is the only mammal that exists.
And while it seems like people talk of abstraction and generalization as two distinct things, I can't think of how one can generalize without abstracting out some property.