To me It seems like you payed too much.
I bought this stuff https://www.amazon.com/Harris-500K-Al-Solder-Aluminum-Solder/dp/B001HWFM9Y/ref=sr_1_2?ie=UTF8&qid=1549161541&sr=8-2&keywords=Harris+500K+Al-Solder+500+Aluminum+Solder when i was splitting lipo batteries and it was the only way i could...