Every aluminium grade is defined by a table of element limits, normally given as minimum and maximum percentages for silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium and others, with aluminium as the remainder. For pure grades such as P1020 the key figure is Al purity %; for alloys the ranges of the main alloying elements decide properties, and impurity limits decide quality.
Why it matters when buying
- Small deviations change behaviour: excess iron makes castings brittle, excess copper hurts corrosion resistance, and trace titanium or vanadium lowers conductivity in EC grade.
- State the standard you buy to (IS, BS, JIS, EN or AA) because limits for the "same" alloy differ slightly between standards.
- Ask for a spectro report or mill test certificate for every heat or lot.
- For scrap, composition determines which alloys the metal can be remelted into, and so its value.
Notes
Chemistry is a core field in a good RFQ; see how to write an aluminium RFQ. Composition is adjusted in the furnace with primary metal and master alloys.