Array to string conversion error to replace two elements

I have this code:

<?php
$url_constructor = "http://ift.tt/1WZI4oY";
$cart_line_link = str_replace($url_constructor, array(
    'article_id',
    'article_name'
) , array(
    $line['article_name'],
    $line['article_id']
));

I need replace the /article_name and /article_id by the cart lines variables.

I want get a result like this example with article: "http://ift.tt/24aTzZ6"

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