Hi, can someone explain to my small brain what reaction this is or what happened? ( imgur.com )

skillissuer , 11 months ago

you’re seeing elecrochemical corrosion. if you scratch aluminum in such a way that:

• oxide layer is removed, and
• finely divided copper is deposited, and
• oxide layer can’t reform

you’ll see rapid corrosion of aluminum. normally, alumnium doesn’t corrode because of very tight oxide layer. here, oxide layer is removed first by scratching and this also deposits copper in electrical contact with aluminum. then, citrate can bind aluminum removing some of oxide layer, making aluminum more exposed and so more reactive. if you used gallium as heat transfer compound (sp?) then gallium will also disturb oxide layer and make corrosion of aluminum faster. copper elements are in this case actually protected from corrosion (by dissolving aluminum)