What is the chemical formula for duralumin? Not what it is made of; something like Co2.

The main alloying constituents are copper, manganese, and magnesium. A commonly used modern equivalent of this alloy type is AA2024, which contains 4.4% copper, 1.5% magnesium, 0.6% manganese and 93.5% aluminium by weight. Typical yield strength is 450 MPa

If you do the math you can figure out the chemical formula. Just use the empirical formula