If your part starts as an extruded profile before any chip-making operation touches it—a heat sink, an enclosure rail, a trim piece—start with 6063 (AlMg0.7Si, EN AW-6063). It is not the strongest 6xxx alloy, but it is the most extrudable. That matters more than you think: the same composition that flows through a die at high speed also shapes how the material behaves when you clamp it in a vise and put a cutter to it.
The practical consequence for a CNC shop is this: 6063 arrives with a fine, uniform grain structure inherited from the extrusion process. It is less abrasive on tooling than 6061. It anodizes to a deeper, more consistent finish. And it costs less per kilogram—by roughly 5–15% depending on profile complexity and market—because it extrudes faster. If your part does not need the full 310 MPa ultimate tensile strength of 6061-T6, you gain more from 6063’s formability and surface quality than you lose in strength.
This article walks through the composition, condition-specific properties, and CNC machining behavior of 6063 aluminum, with a practical focus on what to specify on a drawing and what to expect at the spindle.
Grade Identity and Standards
6063 sits in the Al–Mg–Si (6xxx) family. Its strengthening comes from Mg₂Si precipitates—not from copper additions, which distinguishes it from 2xxx alloys, and not from zinc, which separates it from 7xxx. The key standards are:
- EN 573-3:2019 — Chemical composition (designation EN AW-6063 / EN AW-Al Mg0.7Si)
- EN 755-2:2016 — Mechanical properties for extruded bars and sections
- ASTM B221-21 — Aluminum-alloy extruded bars, rods, wire, profiles, and tubes
- ASTM B209/B209M-21 — Sheet and plate (though 6063 is primarily an extrusion alloy)
- ISO 6362-2:2014 — Wrought aluminium alloy extruded profiles — mechanical properties
- GB/T 5237.1-2017 — Chinese national standard for architectural aluminum alloy extruded profiles
- JIS H 4100:2016 — Japanese Industrial Standard for extruded shapes
Approximate international equivalents: AA6063 (USA), EN AW-6063 (Europe), A6063 (JIS), LD31 (older Chinese designation, now aligned with GB/T 3190). These are near-equivalents with slight composition range differences; treat them as “same family” rather than drop-in interchangeable without checking the specific standard version called on the drawing.
Chemical Composition (EN 573-3, Weight %)
| Element | EN AW-6063 Min (%) | EN AW-6063 Max (%) | Role |
|---|---|---|---|
| Si | 0.20 | 0.60 | Forms Mg₂Si precipitates; controls strength and extrudability |
| Fe | — | 0.35 | Impurity; excess forms AlFeSi intermetallics that reduce anodizing quality |
| Cu | — | 0.10 | Kept low to maintain corrosion resistance |
| Mn | — | 0.10 | Minor; controls grain structure during extrusion |
| Mg | 0.45 | 0.90 | Primary alloying element; forms Mg₂Si with silicon |
| Cr | — | 0.10 | Trace; suppresses grain growth |
| Zn | — | 0.10 | Impurity; kept low |
| Ti | — | 0.10 | Grain refiner |
| Others (each) | — | 0.05 | — |
| Others (total) | — | 0.15 | — |
| Al | Remainder | Balance | |
The Mg₂Si stoichiometric ratio is 1.73:1 (Mg:Si by weight). In 6063, the Mg content (0.45–0.90%) and Si content (0.20–0.60%) typically produce a slight excess of silicon, which improves age-hardening response and strength. If the Mg/Si ratio drifts too far from the ideal band—either from mill variation or re-melt scrap mixing—the as-quenched hardness and subsequent aging response shift measurably. High-purity 6063 variants (sometimes called “6063A” with tighter iron limits ≤0.15–0.25%) are common for bright anodizing applications.
Mechanical Properties by Temper
6063 is almost always used in an artificially aged condition. The properties below are for extruded profiles per EN 755-2; values for sheet or drawn tube under different standards may differ slightly.
| Temper | Tensile Strength Rm (MPa) | Yield Strength Rp0.2 (MPa) | Elongation A50mm (%) | Typical Hardness (HBW) |
|---|---|---|---|---|
| T4 (solution treated + naturally aged) | ≥130 | ≥65 | ≥14 | ≈45 |
| T5 (cooled from extrusion + artificially aged) | ≥175 | ≥130 | ≥8 | ≈60 |
| T6 (solution treated + artificially aged) | ≥215 | ≥170 | ≥8 | ≈73 |
| T66 (solution treated + artificially aged — higher level) | ≥245 | ≥200 | ≥8 | ≈80 |
A few practical distinctions deserve attention:
T5 vs. T6. T5 material is cooled directly from the extrusion press temperature and then artificially aged—no separate solution heat treatment. This saves cost and reduces distortion risk, but the properties are contingent on the exit temperature being high enough to retain alloying elements in solution. If the extrusion exits too cold (common in thin-walled profiles run at borderline speeds), the subsequent age-hardening response can be underwhelming. T6 adds a dedicated solution treatment step (520–530°C, water quench) that guarantees full dissolution; the result is higher and more consistent strength, but with added quench distortion that CNC shops then have to machine out.
T66. T66 is not simply “T6 but harder.” It is an EN 755 designation for material that has been solution-treated, quenched, and aged to a higher strength level than standard T6. The elongation minimum remains the same (8%), so the higher strength comes primarily from optimized aging parameters—typically a two-stage or longer-duration aging cycle below 200°C. If your drawing says “6063-T66,” verify the profile supplier actually runs this cycle; the mill certificate should show both T66 and the achieved properties.
These are minimum values from the standard. Well-controlled commercial extrusions often exceed them by 5–15%. But do not base a dimensionally critical machining plan on an assumption of “extra” strength—use minimums for conservative design and verify with the certificate.
Corrosion Resistance and Anodizing Behavior
6063 has intrinsically good atmospheric corrosion resistance because it contains virtually no copper (≤0.10%). In the 6xxx family, copper is the element most detrimental to corrosion performance; 6061, with up to 0.40% Cu, is measurably more susceptible to intergranular attack in marine or industrial atmospheres. For architectural components exposed to rain, humidity, or mild industrial fallout, 6063 consistently outperforms 6061 in long-term outdoor exposure data compiled in ASTM STP 1529.
But the real reason architects and product designers specify 6063 is anodizing quality. The low iron limit (≤0.35%) keeps the population of AlFeSi intermetallic particles low. These particles do not anodize—they remain as dark specks in the anodic layer. In cosmetic anodizing (clear, champagne, bronze, black architectural finishes per EN 12373-1 / ISO 7599), fewer iron-bearing particles means a cleaner, brighter appearance. 6063’s chemistry also produces a more transparent anodic film than the slightly yellow-tinged film typical of 6061, a difference visible even to untrained eyes when comparing side-by-side parts under fluorescent light.
The trade-off: 6063 should not be selected for components immersed in seawater or aggressive chemical environments. Its Mg₂Si strengthening phase is anodic to the aluminum matrix, meaning micro-galvanic cells can form at precipitate boundaries under sustained chloride exposure. For those conditions, a 5xxx alloy like 5052 (AlMg2.5) or 5083 is typically a safer choice.
CNC Machining Characteristics of 6063
What the Material “Feels Like” at the Spindle
6063 is softer and more ductile than 6061-T6. At T5 or T6 temper, its machinability rating is approximately 50% of free-cutting brass (C36000), compared to roughly 55% for 6061-T6. The difference may not sound dramatic, but it shows up in two specific ways that matter during setup:
Built-up edge (BUE). The combination of relatively low hardness (~60–73 HBW) and high ductility means aluminum can cold-weld to the cutting edge, especially with uncoated carbide or dull tools. A chip that fails to clear the flute can start a BUE event within seconds, ruining surface finish and shifting the effective cutting geometry.
Burr formation. 6063’s elongation at fracture (8–14% depending on temper) means the material extrudes forward of the cutting edge rather than shearing cleanly. Top-edge burrs on milled pockets and exit burrs on drilled holes are larger than on 6061-T6. Deburring adds cycle time—plan for it, or design the toolpath to push the burr into a non-functional edge.
Starting-Point Machining Parameters
The values below are starting references for carbide tooling on a rigid CNC machining center or turning center with adequate flood coolant. Actual parameters depend on machine rigidity, workpiece clamping, tool stickout, coating, coolant pressure, and the specific profile geometry. These are not guaranteed production recipes.
| Operation | Tool | Cutting Speed Vc (m/min) | Feed per Tooth fz (mm) | Depth of Cut ap/ae (mm) | Coolant |
|---|---|---|---|---|---|
| Facing / Shoulder milling | Carbide insert, polished uncoated (K10/K20 grade) | 300–800 | 0.10–0.25 | ap ≤ 4.0 | Flood emulsion 5–8% |
| Profile / slot milling | Solid carbide, 2 or 3 flute, polished flute | 200–500 | 0.05–0.15 | ae ≤ 0.4×D, ap ≤ 1.0×D | Flood or MQL |
| Drilling | Carbide drill, polished flute, 118° or 130° point | 100–250 | 0.08–0.25 | — | Through-coolant or flood |
| Tapping | Spiral-flute HSS tap or form tap | 10–25 | Per pitch | — | Flood emulsion |
| Turning (external) | Carbide insert, polished uncoated, positive rake | 250–600 | 0.08–0.25 mm/rev | ap 1.0–4.0 | Flood |
Tooling Notes
Polished uncoated carbide inserts and end mills typically outperform coated tools (TiN, TiAlN) on 6063. The aluminum has no chemical affinity for the polished carbide surface, and uncoated tools allow sharper cutting edges because the edge radius is not rounded by the coating thickness. If coating is necessary for a mixed-material production environment, a thin-film diamond-like carbon (DLC) or ZrN coating is the least problematic choice.
For exotic geometries with deep pockets or thin walls, check for the same workholding considerations that apply to 6061: 6063 work-hardens negligibly compared to austenitic stainless steels, but it is prone to chatter in thin sections due to its relatively low elastic modulus (~69 GPa). Use the shortest possible tool stickout and, for wall thicknesses below 3 mm, consider stepped roughing passes instead of finishing directly from the extrusion surface.
Heat Treatment Considerations for Machining
Understanding the condition the material was delivered in changes how you should sequence work:
Machining in T5. T5 is the default commercial temper for standard architectural profiles. It offers decent machinability and does not require heat treatment after roughing. However, if internal stresses from the extrusion cooling process are significant—visible as bow or twist in the as-received profile—rough machining can release these stresses and cause the part to warp. For long, slender parts machined from T5 extrusions, a stress-relief cycle (200–240°C for 1–2 hours, slow cool) before finish machining can cut post-machining distortion by a noticeable margin, though it may slightly reduce the T5 strength.
Machining in T4, then aging to T6. This is a legitimate strategy for complex geometry: rough-machine while the material is soft (T4, ~45 HBW), then artificial-age to T6 (or T66) to develop final strength, then finish-machine. The aging cycle is typically 175–190°C for 6–8 hours (T6) or longer at slightly higher temperature for T66. Expect a dimensional change of roughly 0.05–0.15% from the aging cycle—enough to matter on tight-tolerance bores or bearing fits. Leave a finish stock of at least 0.25 mm to clean up post-aging distortion.
Surface Finish After Machining and Anodizing
As-machined surface finish on 6063 can reach Ra 0.4–0.8 μm with sharp tooling, correct speeds, and adequate chip evacuation. The material is forgiving—more so than 7075 or 2024—because the soft Mg₂Si precipitates do not tear the surface the way harder intermetallic phases do in higher-strength alloys.
If the part will be anodized after machining, note one critical point: the anodic layer grows approximately 50% inward and 50% outward from the original surface. A 20 μm anodic coating (common for architectural use, Class II per ISO 7599) will consume roughly 10 μm of substrate and add 10 μm above the original surface. Threaded holes, press-fit bores, and bearing seats must account for this growth. For a standard M6-6H thread before anodizing, a 10 μm buildup may push the thread outside the Go gauge tolerance—either cut the thread slightly oversized before anodizing or protect it with a masking plug.
Applications Where 6063 Outperforms Alternatives
The selection logic for 6063 is different from 6061. You pick 6063 when the part is shaped more than it is loaded. Specific cases include:
- Heat sinks. 6063’s thermal conductivity (approximately 200–210 W/m·K in T5 temper) is competitive with 6061 (~167 W/m·K) and its extrudability allows thinner, taller, and denser fin geometries that increase surface area without adding weight. For a given envelope, a 6063-T5 extrusion can typically pack 20–30% more fin density than a 6061 extrusion before die life or extrusion speed becomes prohibitive.
- Architectural framing, railings, and trim. These are governed by stiffness and appearance, not ultimate strength. 6063 anodizes to a superior cosmetic finish, and the elastic modulus (~69 GPa) is the same as every other aluminum alloy—there is no stiffness penalty for choosing the more formable grade.
- Consumer electronics enclosures. Laptop frames, monitor bezels, and camera bodies use 6063 because the anodizing quality is visible at arm’s length. These parts often require CNC machining of mounting bosses, connector cutouts, and precision alignment features after extrusion.
- Pneumatic and hydraulic manifold blocks. When internal passages are drilled rather than cast, 6063’s lower hardness and uniform grain structure reduce drill wander in long, small-diameter holes compared to 6061-T6.
- LED lighting profiles and thermal rails. The extrusion cross-section is often the final aesthetic surface. 6063-T5 delivers the required heat dissipation, anodizing quality, and the dimensional consistency needed to snap-fit diffusers and end caps without secondary gasketing.
- Solar panel framing. Structural requirements are stiffness-driven (wind load deflection), not strength-driven. 6063-T5 or T6 extrusions dominate this application globally due to the combination of low cost per meter, adequate modulus, and long-term atmospheric corrosion resistance without protective coating.
6063 vs. 6061: A Practical Comparison
These two alloys are frequently considered side by side. The comparison below is for material in the T6 temper unless stated otherwise:
| Property | 6063-T6 | 6061-T6 | What It Means |
|---|---|---|---|
| Tensile Strength (min, MPa) | 215 | 260 | 6061 is ~20% stronger; pick it if strength governs section thickness |
| Yield Strength (min, MPa) | 170 | 240 | 6061 takes higher stress before permanent set |
| Elongation (min, %) | 8 | 8 | No practical difference in ductility at T6 |
| Copper content (%) | ≤0.10 | 0.15–0.40 | 6061’s added Cu improves strength but reduces corrosion resistance and anodizing clarity |
| Extrusion speed (relative) | High (~30–60 m/min) | Moderate (~15–30 m/min) | 6063 is cheaper to extrude complex profiles |
| Anodizing quality | Excellent, bright, clear | Good, slightly yellow tint | 6063 wins on visible surfaces |
| Thermal conductivity (W/m·K) | ~200–210 | ~167 | 6063 dissipates heat ~20% better |
| Machinability (relative) | ~50% of C36000 | ~55% of C36000 | 6061 is slightly easier to machine; 6063 is slightly gummier |
For CNC machining 6061, you get marginally better chip breaking and less tendency for BUE—at the cost of faster tool flank wear from the harder, more abrasive Mg₂Si/Cu intermetallic phases. Neither alloy is difficult to machine, but the failure modes are different: 6063 gums, 6061 wears.
A common mistake is specifying 6061-T6 for extruded parts that will never see the yield stress 6061 provides. If your part is stiffness-limited (deflection governs wall thickness, not strength) and will be anodized for appearance, 6063-T5 or T6 almost always results in a cheaper extrusion with a better-looking anodized finish.
What to Put on Your RFQ or Drawing
When requesting a quote for CNC-machined 6063 parts, include the following to avoid back-and-forth delays:
- Alloy and temper: Specify the exact designation (e.g., “EN AW-6063 T5” or “AA6063-T6”) and the standard you require the material to meet (EN 755, ASTM B221). Do not write just “6063”—the temper changes mechanical properties by 30–40%.
- Extrusion source: Indicate if you are supplying the extrusion or if the shop sources it. Extrusion die condition affects as-received straightness and surface quality.
- Anodizing specification: If post-machining anodizing is required, specify the coating type, thickness class (e.g., ISO 7599 Class II, 15–20 μm), and colour. Mention whether threads and bores are to be masked.
- Critical tolerances: Mark which dimensions control fit/function. 6063-T5 can achieve ±0.05 mm on turned diameters with a rigid setup, but tolerances below ±0.02 mm will increase scrap rate and cost—especially on long parts where extrusion straightness becomes the limiting factor.
- Surface roughness: Specify Ra in μm on functional surfaces. As-machined Ra 0.8–1.6 μm is practical; Ra 0.4 μm requires additional care.
- Quantity and batch: Single prototypes, small-batch (10–100), or production runs (1000+). Setup strategy and tool life economics change drastically across these scales.
- Material certificate requirement: EN 10204 3.1 or 2.2 inspection certificate. State this explicitly—shops may not default to providing mill certificates unless asked.
If you have a drawing ready, upload it here for a review along with the material spec, temper, tolerances, and surface finish requirements. We’ll confirm feasibility and provide a detailed quote.
Turn this machining question into a manufacturable part
Need this material or process for your next CNC project?
Send your STEP, STP, IGES, DXF, PDF, material, quantity, surface finish, and tolerance requirements. We will review manufacturability and reply with practical quotation guidance.
