What aluminum alloy numbers mean (1100, 3003, 3105, 5052)

Buyers order aluminum by alloy number without always knowing what sits behind it. The number is not a catalog code: it describes the chemistry of the metal, and from that chemistry come strength, ductility, weldability and price.

What each digit says

The Aluminum Association maintains the four-digit system the whole industry uses. The first digit names the main alloying element. The next three identify the specific alloy within the series, and in the 1000 series the last two digits give purity: 1050 is 99.50% aluminum, 1100 is 99.00%.

Series a common-alloy mill does not make

The 2xxx (copper), 6xxx (magnesium and silicon) and most 7xxx series are heat-treatable: they gain strength through solution treatment and aging. They are the alloys of aerospace and automotive outer body panels. Almexa makes common, non-heat-treatable alloys, and says so before quoting so nobody waits a week for a 6061 that will never come.

What each element adds

Manganese in the 3000 series raises strength without giving up much formability; that is why 3105 dominates building products, and 3004 dominates cookware bases and cans. Magnesium in the 5000 series raises strength further and improves behavior in salt water; 5052 is the alloy of truck boxes, tanks and structural transport parts. Iron and silicon in the 8000 series allow rolling to foil gauges; those are foil alloys, and Almexa does not make them.

Temper is the other half of the number

An alloy is ordered with its temper: O is annealed, the softest condition; H12, H14, H16 and H18 are strain-hardened in increasing degrees; H2x are strain-hardened and partially annealed. Two 3105 coils can behave like different materials if one is O and the other H18: the first draws, the second cracks on the same radius. When a bend fails, the first question is not the alloy, it is the temper.

How to choose when you don't know

• Deep-drawn parts (pots, steamers): 1050 or 1100 in O temper.
• Painted and formed parts (profiles, panels, blinds): 3105 in H14 or H16.
• Parts needing rigidity or going on trucks: 5052 or 5754 in H32 or H34, up to 36 in wide.
• Electrical components: 1350.

When doubt remains, the right answer is to send the part, not the alloy. A plant metallurgist looks at it and proposes the alloy and temper combination, which is sometimes cheaper than the one you had written down.

What the number doesn't say

The number doesn't say who melted the metal or with what scrap. Two 1100s from two mills meet the same composition standard and can differ in inclusions, flatness and gauge consistency. That difference shows in the lot's mill test report and on the customer's line, not on the purchase order.