Aluminium coin bubbles

Not sure if this is exactly the right forum. I found this 1954 5 Lira in a bulk lot and I just want to know what the heck could have caused these bubbles to form, they are very prominent on the obverse, even more so than in the photo. Does anyone have any idea or have they seen this before?

I'm not sure whether this is PMD (post-mint damage) or an actual error, but on the French side there were several examples of aluminium coins with "bubbles", though nothing like coins entirely covered with such bubbles.

At first sight it looks to me like some sort of corrosion, and therefore PMD. The fact that both sides are affected would also argue for post-mint damage. What about the rim? If it is nice and clean, then the likelihood that it is a mint error becomes more likely.

I've seen similar bubbles at aluminium coins as well,in all cases they were caused by corrosion.

Quote: "AcrateofTuna"​Not sure if this is exactly the right forum. I found this 1954 5 Lira in a bulk lot and I just want to know what the heck could have caused these bubbles to form, they are very prominent on the obverse, even more so than in the photo. Does anyone have any idea or have they seen this before?
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​Hello
In my opinion -into the parent metal of aluminum was given another metal to improve the properties (hardness , etc.) usually there are other admixtures in each coin metal, if zinc (or other metal in a small amount )is so in the parent metal when contacted by a chemical environment it can cause such damage
also my friend ALLRED1950 advised me:
https://en.numista.com/forum/topic62382.html

here is the problem under the copper plate:

Ahoj
Ivan

Thanks for the replies. Camerinvs, the rim is fine, no bubbles there. MIMAEL, that certainly sounds like a plausible explanation so I'll accept that. I think it looks neat and I think I'll be keeping it as the inaugural item in my ugly oddities collection.