Links and associations can't be used interchangeably because
association is a relationship among classes and link is a
relationship among instance of classes.
e.g. => Person works for company. 
Here a connection exists  between two classes 'person' and
'company' so this is the example of association but if we
take one instance of each of the above classes as 'Ram' and
'Google' then we can be specific about the work which Ram is
doing for Google.
e.g. => Ram works as a programmer for Google.
But we cant use 'Person works as a programmer for Google'.
Hence we can't use links and associations interchangeably.