Is the aluminium coated with plastic? If so bleach would be OK but otherwise I would be cautious. I know bleach on stainless is a bad idea, I'm not sure about aluminium.
i have reused the 5l kegs and primed them to use in my beer cooler(a much fancier version of lidl's) and they seem to work out fine. i prime them and then tap them with co2 when i wanna drink em through the cooler. great for parties or when you are low on bottles.
