I usually use the coconut's water for badly corroded blades. It may take a week or two on your blade. Use the water of ripe coconut, not the unripe/young ones, undiluted. Make sure the blade all submerged, or you will got a nasty rust on the water line. Check the blade at least once a day and brush off any loose rust produced. You may add some lime juice, but it is optional. Prepare for a nasty smell !
I work solely with coconut's water and lime juice, and have never used pineapple juice, so don't know anything about it. I prefer to eat the pineapple as rujak salad rather than use it to clean the blade
Good luck !