Aluminum 2017 - AlCu4MgSi - AL4

2017 aluminum alloy: AA 2017 and EN AW 2017A variants

The 2017 aluminum alloy belongs to the family of wrought aluminum alloys that harden by precipitation. Two main variants should be distinguished:

• AA 2017 — the U.S. designation (Aluminum Association), also listed as UNS A92017.
• EN AW 2017A — the standardized European designation (EN 573 3), also known as AlCu4MgSi(A) and corresponding to the German Werkstoff number 3.1325.

Although very similar and often regarded as equivalent, these grades differ slightly in chemical composition, which determines the applicable standards.

2017 vs. 2017A: virtually identical chemical compositions

2017 and 2017A share the same aluminum–copper base alloy with additions of magnesium, manganese and silicon. The only notable differences are:

• Magnesium (Mg) — 2017A allows up to 1.0 % Mg, whereas 2017 is limited to 0.8 %. Because magnesium promotes the formation of hardening precipitates, this extra margin can yield slightly higher strength when Mg is at its upper limit.
• Titanium and zirconium (Ti, Zr) — 2017 caps titanium at 0.15 % and makes no provision for zirconium (generally absent or treated as an impurity). 2017A permits a combined Ti + Zr content of up to 0.25 %, meaning it may contain small additions of one or both elements, which refine the grain structure in certain products.

In practice, the two grades have nominally equivalent chemistries; the extra Mg allowance and the option to add Zr are minor variations.

Physical properties of 2017A — strengths and weaknesses

Like most high‑strength aluminum alloys, 2017A has a low density of about 2.80 g/cm³ — roughly one‑third that of steel. Its light weight combined with an ultimate tensile strength of around 400 MPa in the T451 temper makes it attractive for weight‑critical structures.

Thermal conductivity is moderate, roughly 140 W·m⁻¹·K⁻¹ at room temperature — well below the ~237 W·m⁻¹·K⁻¹ of pure aluminum. Electrical conductivity is likewise reduced: about 34 % IACS, or one‑third that of pure copper. Dispersed alloying elements and hardening precipitates impede both heat and electron flow.

Corrosion resistance rates only fair to poor by aluminum standards. The ~4 % copper in the matrix forms galvanic micro‑cells that accelerate attack in humid or saline environments, making 2017A less durable than 5000 or 6000 series alloys. It performs adequately in mild atmospheres but needs anodizing or another coating for marine or damp service to prevent surface and intergranular corrosion. Protective anodizing is feasible, yet the high copper content yields poor decorative results (uneven color, brownish cast).

While 2000 series alloys retain their strength better than, say, 7000 series alloys at moderate temperatures (100–150 °C), their precipitation hardening deteriorates quickly above that range. The alloy’s melting interval lies between 513 °C and 641 °C.

Applicable heat treatments

The 2017 series belongs to the precipitation‑hardenable (solution treated + aged) structural aluminum family. Both variants (2017 and 2017A) reach comparable strength levels under identical heat treatments; any differences fall within normal variability. (For a detailed side‑by‑side comparison, see the MIF infographic.)

The most common tempers are:

1. Annealed (O) — 2017 is relatively soft and highly ductile, making forming and deep drawing easier, but its strength is very low.
2. Solution treated and naturally aged (T4) — after a few days, the alloy stabilizes in the T4 condition (also called naturally aged AU4G), achieving high strength while retaining moderate ductility.
3. T3 — a solution treatment followed by cold working (strain hardening) before natural ageing, which slightly raises the yield strength.
4. Artificial ageing (T6) — less common for 2017 than for alloys such as 2014 or 2024, the T6 temper delivers maximum tensile strength at the expense of ductility.

In short, 2017A in the widely used T4 temper offers an excellent strength‑to‑ductility balance, whereas the T6 temper maximizes mechanical strength — well‑suited to heavily loaded parts — at the cost of lower toughness.

2017 in practice — machinability, formability, weldability

The 2017 alloy is well known for its excellent machining behavior; it can be formed when the temper is chosen carefully, but welding is problematic. Variant 2017A behaves much the same.

Machinability

2017 machines very well, especially in the T4 or T6 temper, where the metal is harder and chips break cleanly. Its machinability rating is 90 % in T4 (60 % in O), using alloy 2011 as the 100 % benchmark, making it easier to machine than most common aluminum.

Formability

Formability depends heavily on temper. In the annealed (O) condition ductility is good, allowing bending and deep drawing. In the solution treated and aged states (T4/T6), the alloy is harder and less suited to large deformations without cracking. When major shaping is required, parts are best formed immediately after quenching, while still in the W condition (before full hardening).

2000 series alloys are also poorly suited to cryogenic service or forming, as they lose toughness when cold.

Weldability

Welding 2017/2017A is generally tricky. The high copper content fosters low‑melting phases that lead to:

• hot cracking in fusion welding (TIG, MIG);
• dissolution of hardening precipitates in the weld pool, reducing strength;
• loss of corrosion resistance.

Fusion welding is therefore discouraged. Only resistance welding (spot, seam) is recommended. Spot welding works fairly well because the molten zone is very brief and highly localized.