Aluminum coils are categorized into different grades based on their alloy composition and applications. The most common grades include 1000 series (99% pure aluminum), 3000 series (aluminum-manganese alloys), 5000 series (aluminum-magnesium alloys), and 6000 series (aluminum-magnesium-silicone alloys). Each grade has unique properties such as formability, strength, and corrosion resistance, which make them suitable for specific applications like construction, transportation, and packaging. The selection of the grade depends on the performance requirements of the end product.