Who Should Consider 2017 (AlCu4MgSi) Over More Common Alloys
If your CNC-turned part needs higher strength than 6061-T6 can deliver and you cannot justify the cost of 7075, look closely at 2017 in the T4 condition. EN AW-2017A, designated AlCu4MgSi under EN 573-3, belongs to the 2xxx (Al-Cu-Mg) family. It bridges a specific gap: roughly 390 MPa ultimate tensile strength with machinability that most shops find easier than 2024-T3. The trade-off is lower corrosion resistance than 6xxx alloys and no fusion weldability. This article walks through what that means for your drawing, your toolpath, and your inspection report.
Grade Designations and the Standards That Define Them
Material identity matters when you are writing an RFQ. The following designations all point to the same alloy family, but do not assume interchangeability without verifying temper:
- EN AW-2017A — European standard designation per EN 573-3 (wrought aluminium alloy). The “A” suffix indicates a composition variant with tighter impurity limits than the original 2017.
- AlCu4MgSi — Numeric chemical symbol per EN 573-3, directly encoding the four principal alloying elements.
- AA 2017 — Aluminum Association (USA) designation per ANSI H35.1. Note that AA 2017 and EN AW-2017A have slight compositional differences, particularly in magnesium and manganese ranges.
- 3.1325 — Werkstoffnummer (Germany), used in DIN legacy documentation.
- A-U4G — Historical French designation (AFNOR), still seen on older aerospace drawings.
It is not a direct substitute for 2024 (AlCu4Mg1) or 2014 (AlCu4SiMg). Each 2xxx variant solves a different problem. 2017 sits between 2014 and 2024 in terms of strength, with its own machining signature that experienced operators recognize immediately.
Chemical Composition: What the Melt Specification Says
EN 573-3 defines the composition of EN AW-2017A. The copper content drives both the strength and the corrosion sensitivity:
| Element | EN AW-2017A (wt%) per EN 573-3 |
Role in This Alloy |
|---|---|---|
| Cu | 3.5 – 4.5 | Primary strengthening element; forms Al2Cu precipitates during natural aging |
| Mg | 0.40 – 1.0 | Works with Cu to refine precipitate distribution; increases as-aged strength |
| Si | 0.20 – 0.8 | Promotes Mg2Si formation; excess Si can embrittle grain boundaries |
| Mn | 0.40 – 1.0 | Forms Al12Mn3 dispersoids; controls grain size and raises recrystallization temperature |
| Fe | ≤ 0.70 | Impurity; forms Al3Fe intermetallics that reduce ductility |
| Zn | ≤ 0.25 | Trace; above this threshold can alter aging kinetics |
| Ti + Zr | ≤ 0.25 | Grain-refining additions; keep fine and dispersed |
| Other (each) | ≤ 0.05 | — |
| Other (total) | ≤ 0.15 | — |
| Al | Remainder | Matrix |
A practical note for incoming inspection: if your supplier certifies against EN 573-3, the cert shows both the EN AW number and the chemical symbol. If the cert only lists a proprietary trade name with no normative reference, ask for a 3.1 certificate per EN 10204 that traces back to the cast analysis.
Mechanical Properties: Room-Temperature Numbers That Matter
2017 is almost always ordered and machined in the T4 temper: solution heat treated at approximately 495–505 °C, quenched, and naturally aged to a substantially stable condition. Data below is for extruded or rolled bar up to 100 mm section thickness, tested per EN 485-2 / ISO 6892-1 at room temperature:
| Property | T4 (Typical) | Test Method |
|---|---|---|
| Tensile strength, Rm | 370 – 390 MPa | ISO 6892-1, A50 specimen (ø ≤ 100 mm) |
| Yield strength, Rp0.2 | 240 – 260 MPa | ISO 6892-1, 0.2% offset |
| Elongation, A5 | 12 – 15% | ISO 6892-1, gauge length 5×diameter |
| Brinell hardness | 100 – 110 HBW | ISO 6506-1, 2.5 mm ball / 62.5 kgf |
| Modulus of elasticity | ~73 GPa | Ultrasonic / resonance method |
| Shear strength | ~220 MPa | Double-shear fixture (typical, not a standard minimum) |
| Fatigue strength (rotating beam, 5×108 cycles) | ~125 MPa | ISO 1143; polished R.R. Moore specimen |
| Density | 2.79 g/cm3 | Archimedes method |
These values are typical for wrought bar stock in T4 condition. T3 (cold-worked after solution treatment) raises strength slightly but is uncommon in the supply chain. If your part is machined from plate, properties in the short-transverse direction can drop 5–10% from the longitudinal values shown here.
How T4 Aging Works — and Why You Cannot Accelerate It
2017 reaches T4 strength through room-temperature natural aging after a solution heat treatment and quench. The aging curve is steep for the first 24–48 hours, then flattens substantially. After roughly four days at 20 °C, the alloy is considered “substantially stable” per most commercial specifications. Unlike 6xxx alloys that respond to artificial aging (T6), 2017 gains nothing from elevated-temperature aging — in fact, heating into the 120–200 °C range coarsens the GP zones that provide strength and can permanently reduce mechanical properties. This matters if your part subsequently sees service above about 100 °C: check that the expected operating temperature will not over-age the material.
Corrosion Behavior: Where 2017 Works and Where It Does Not
The copper that gives 2017 its strength is also its Achilles’ heel in corrosive environments. The galvanic potential difference between the copper-rich precipitates and the aluminum matrix creates micro-galvanic cells in the presence of an electrolyte. Results from salt-spray testing (ISO 9227, neutral 5% NaCl) show pitting initiation within 24–48 hours on unprotected T4 surfaces, compared to hundreds of hours for 6061-T6.
In practice, this means:
- Indoor, dry or oiled environments: Acceptable without coating.
- Outdoor, non-marine: Requires anodizing (sulfuric acid, Type II) or chemical conversion coating per MIL-DTL-5541 Type II. Note that 2xxx alloys do not anodize to the same clear, uniform appearance as 6xxx.
- Marine or chemical exposure: Avoid 2017 entirely. Consider 5083 or 6061 instead, or move to a protective cladding (Alclad 2017) if available.
- Contact with dissimilar metals: 2017 is anodic to most steels and stainless steels. Use isolating washers, wet-installed sealants, or cadmium-plated fasteners.
Stress-corrosion cracking (SCC) susceptibility in the short-transverse direction is moderate in T4 temper. For thick sections (>50 mm) loaded in the through-thickness direction, order material with a controlled forging or rolling reduction ratio and discuss SCC testing with your mill.
CNC Machining 2017: What Happens at the Tool Tip
Experienced machinists describe 2017-T4 as “short-chipping” but “soft enough to smear.” The chips break cleanly because the Al2Cu precipitates act as internal chip breakers, but the low hardness (≈105 HBW) means built-up edge (BUE) forms readily on uncoated carbide if cutting temperatures are too low or coolant is intermittent.
The starting parameters below assume a modern CNC lathe or 3-axis VMC with adequate spindle power and flood coolant. They are starting references only — machine rigidity, tool overhang, workholding, and batch quantity will shift every number:
| Operation | Cutting Speed | Feed Rate | Depth of Cut | Tooling Suggestion |
|---|---|---|---|---|
| Rough turning | 250 – 400 m/min | 0.15 – 0.40 mm/rev | 1.0 – 4.0 mm | Uncoated fine-grain carbide, positive rake (γ = 12–18°), clearance ≥ 8° |
| Finish turning | 300 – 500 m/min | 0.05 – 0.15 mm/rev | 0.2 – 0.8 mm | PCD or polished carbide with sharp edge (no hone > 10 µm) |
| Face milling | 300 – 600 m/min | 0.10 – 0.25 mm/tooth | 0.5 – 3.0 mm | 45° lead-angle face mill, PCD or uncoated carbide inserts, flood coolant |
| End milling (slot) | 150 – 300 m/min | 0.03 – 0.10 mm/tooth | ≤ 0.5×D radially | 2- or 3-flute solid carbide, polished flutes, minimum runout |
| Drilling (ø 3–12 mm) | 80 – 150 m/min | 0.08 – 0.25 mm/rev | — | Carbide drill with internal coolant; peck cycle for L/D > 5 |
| Reaming | 20 – 40 m/min | 0.2 – 0.5 mm/rev | 0.1 – 0.3 mm radial | Carbide reamer, spiral flute, generous coolant flow |
| Tapping (blind) | 10 – 20 m/min | Pitch-dependent | — | Spiral-flute tap with TiN coating; avoid forming taps in 2017 |
Coolant Strategy
Flood coolant (5–8% emulsion concentration, water-miscible semi-synthetic) is the default. The primary job is chip evacuation and preventing BUE, not heat removal — aluminum conducts heat away from the cutting zone efficiently. For deep-hole drilling or pocket milling with limited chip clearance, through-tool coolant at 20+ bar makes a measurable difference in tool life and hole straightness. MQL is not recommended for 2017 roughing operations because the high affinity of copper-rich phases for tool material demands consistent lubrication.
Burr Control
2017-T4 forms fine, rolled-over burrs on exit edges. Unlike the brittle burrs of cast aluminum, these do not snap off cleanly. On thin-walled parts or intersecting bores, consider a secondary deburring pass with a small-radius chamfer tool or a manual thermal deburring step. Leaving a 0.1–0.2 mm witness land and removing it with a sharp finishing pass reduces the burr root size compared to taking everything in one cut.
Surface Treatment Options After Machining
2017 responds differently to common aluminum surface treatments than 6xxx or 5xxx alloys:
- Sulfuric acid anodizing (Type II, MIL-A-8625): Produces a darker, more opaque coating than on 6061. Thickness 5–25 µm. The Cu-rich intermetallics partially dissolve during anodizing, leaving a slightly rougher surface. Hard anodizing (Type III) is possible but carries risk of burning at higher current densities — the dissolving Cu phases create localized hot spots.
- Chemical conversion coating (Alodine/Iridite, MIL-DTL-5541): Clear (Type II) or yellow (Type I) chromate conversion works well and provides a conductive surface. This is the most common pre-paint treatment on 2017 parts.
- Electroless nickel plating: Requires a zincate pre-treatment. Adhesion is generally good if the zincate step is double-dipped.
- Painting: Apply a chromate primer (e.g., MIL-PRF-23377 epoxy primer) over a conversion-coated surface. Without conversion coating, the copper-rich surface can cause filiform corrosion under the paint film.
Comparing 2017 to Similar Alloys: When Each One Wins
Engineers often arrive at 2017 after comparing it against 2024, 2014, and 6061. Each comparison must assume the same product form and comparable temper to be valid:
| Property | 2017-T4 | 2024-T3 | 2014-T6 | 6061-T6 |
|---|---|---|---|---|
| Tensile strength (MPa) | 370–390 | 440–480 | 440–480 | 290–310 |
| Yield strength (MPa) | 240–260 | 290–340 | 380–415 | 240–260 |
| Elongation (%) | 12–15 | 12–18 | 8–12 | 10–14 |
| Machinability (relative) | Good — short chips | Good — short chips | Good — short chips | Fair — stringy chips |
| Corrosion resistance | Poor — requires coating | Poor — requires coating | Poor — requires coating | Good — often used bare |
| Weldability | Not recommended | Not recommended | Not recommended | Good — TIG/MIG |
| Typical applications | Machined fittings, rivets, medium-strength structural | Aircraft skin, structural frames | Heavy forgings, truck wheels | General structural, frames, marine |
Choose 2017 over 2024 when: You want easier machinability (less abrasive to tools), you accept the 10–15% lower strength, and availability in your region favors it. In the European supply chain, EN AW-2017A bar stock is more widely stocked than AA 2024.
Choose 6061 over 2017 when: Corrosion resistance or weldability are required, or your operating environment includes moisture.
Choose 2014 over 2017 when: You need higher yield strength (~380+ MPa in T6) and the component will be forged rather than machined from bar.
Practical RFQ Checklist for 2017 Parts
When you send a 2017 part for CNC quotation, include these specifics to avoid the three most common quoting errors: wrong temper assumed, wrong corrosion protection, and wrong inspection criteria:
- Material designation with temper: “EN AW-2017A T4 per EN 573-3/EN 485-2” — not just “aluminum 2017”
- Product form and grain direction: Bar, plate, or extrusion? If loading is directional, specify longitudinal grain orientation on the drawing.
- Surface treatment: Bare, anodized (define thickness and color acceptance), or conversion-coated? State the MIL or ISO spec.
- Tolerances: ISO 2768-m is a reasonable default for turned features; tighter than ±0.02 mm on diameters requires a discussion about process capability with this alloy.
- Surface finish: Ra 1.6 µm is achievable in turning with a finishing pass. Ra 0.8 µm requires grinding or polishing — 2017 does not diamond-turn to an optical finish the way some 6xxx alloys can.
- Quantity: Single prototype, small batch (10–100), or production? This changes the tooling strategy — PCD becomes cost-justified above roughly 5,000 parts.
- Inspection requirements: Dimensional only, or with material cert, hardness check, and surface treatment cert?
- Expected service environment: Temperature range, exposure to moisture or chemicals. This determines whether the part can ship in the as-machined condition or needs post-treatment.
This article was prepared using publicly available data from EN 573-3:2019, EN 485-2:2016, ISO 6892-1:2019, and ISO 6506-1:2014. Machining parameters are suggested starting points and will vary with tooling, machine rigidity, workpiece geometry, and coolant delivery. Always validate with a first-article inspection.
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