Aluminum alloy disc blank for magnetic disc and magnetic disc

An aluminum alloy disc blank for a magnetic disc made of an aluminum alloy comprising Mg:

• 3.40 to 3.90 mass %, Si:
• 0.016 mass % or more and 0.060 mass % or less, Fe:
• 0.020 mass % or more and 0.060 mass % or less, Zn:
• 0.30 mass % or less, and Cr:
• less than 0.10 mass % with a balance being Al and inevitable impurities, wherein a conductivity of the aluminum alloy disc blank for a magnetic disc is 36.0% IACS or higher, wherein the aluminum alloy disc blank for a magnetic disc has a proof stress 90 mPa or more.