SQL Server Audit Action Group:
DATABASE_ROLE_MEMBER_CHANGE_GROUP
This group tracks membership additions and removals on database roles.
If you enable this group in a server audit specification, that will track all new and remove members and database roles in all databases throughout the entire SQL Server instance. If you enable this group in a database audit specification, it will only track membership changes on database roles within that particular database.
LOGbinder for SQL Server
events generated under this
Audit Action Group: