Aluminum

Aluminum is the workhorse non-ferrous metal of modern product development. Its density is 2.7 g/cc — roughly one-third that of steel — yet it machines three to five times faster, accepts a wide range of finishes, and is fully recyclable. About 75% of all aluminum ever smelted is still in active circulation, which keeps base-metal pricing stable and makes it a defensible choice for any climate-conscious BOM.

Wrought alloys use a four-digit code whose first digit names the primary alloying element: 1xxx commercially pure, 2xxx copper, 3xxx manganese, 4xxx silicon, 5xxx magnesium, 6xxx magnesium-silicon, 7xxx zinc, 8xxx lithium or iron. A second code records the temper — the mechanical state produced by cold work or heat treatment. Always specify both; a 5052-H32 marine bracket and a 7075-T651 aerospace fitting share only the base element.

For most CNC enclosures and structural brackets you will default to 6061-T6 with yield strength 276 MPa. When the part must carry higher fatigue loads or tighter tolerances, 7075-T6 lifts yield to 503 MPa at a 2–3x price premium. For stamped chassis, 5052-H32 sheet bends without cracking down to 1x thickness; for extruded heat sinks, 6063-T5 flows cleanly through dies. Cast DMLS parts use AlSi10Mg powder and land somewhere between wrought and cast performance.

Aluminum wins against steel when weight matters and against plastic when stiffness, heat dissipation, or perceived quality matter. A 6061 CNC enclosure typically weighs 65% less than a mild-steel equivalent with the same deflection budget, because stiffness scales with thickness cubed and aluminum tolerates thicker walls at similar mass. That mass savings shows up directly in shipping cost, handheld ergonomics, and structural load paths in vehicles and drones.

Thermal conductivity of 150–210 W/m·K makes aluminum the default material for heat sinks, battery cold plates, and LED bases. Electrical conductivity at roughly 60% IACS supports bus bars and RF ground planes. Corrosion resistance is naturally good thanks to the self-healing Al2O3 oxide; anodizing multiplies that protection and adds colour. Few other metals combine these four attributes — light, stiff, thermally conductive, corrosion tolerant — at under USD 3 per kilogram of billet.

A 150 mm CNC enclosure with internal pockets and tapped holes lands in the USD 80 to 280 range when cut from 6061-T6 billet. Moving to 7075-T6 roughly doubles the material cost and adds 10 to 20% to cycle time because feeds drop to protect tool life. Stainless 304 triples machine time. ABS injection is two orders of magnitude cheaper per part but carries USD 6,000 to 20,000 of tooling before the first shot.

The temper code tells you how the alloy was conditioned: O is annealed and soft, H is strain-hardened sheet, T4 is solution-treated and naturally aged, T6 adds artificial ageing for peak strength, T651 adds a controlled stretch to relieve residual stress — essential when you will machine an asymmetric pocket and want the plate to stay flat.

Aluminum takes well to almost every subtractive and forming process. The right pairing depends on geometry complexity, quantity, and what finish the part must carry afterwards.

When you already know what the part must do, the alloy and process narrow quickly. Use this matrix as a starting point and adjust for any galvanic, thermal, or finishing constraint unique to your assembly.

On CNC parts, keep walls above 0.8 mm and avoid deep, thin ribs where the length-to-thickness ratio exceeds 10:1. Aluminum flexes under cutting forces and chatter will both smear the finish and oversize the pocket. For tall bosses use a 3 mm minimum base radius to keep stress concentrations below the 6061 fatigue limit.

For sheet metal, honour the 1x thickness minimum bend radius on 5052 and 2x to 3x on 6061. Do not bend 7075 — it cracks. Relief cuts at inside corners prevent tears; specify a 0.5 mm hole offset from any bend line so your flatness stays inside 0.2 mm.

For anodized cosmetic surfaces keep every visible face in one alloy. Colour matching between 6061, 7075 and 5052 is poor even with identical dye chemistry because grain structure differs. Call out edge break explicitly, typically 0.3 mm radius or 0.5 mm by 45 degrees, and remember that sharp external edges will not hold anodize film and will show white.

As-machined shows tool lines and is acceptable for internal structural parts. Bead blasting with 120–220 grit glass bead delivers a uniform matte finish in under a minute per face and is the standard prep before anodize.

Type II anodize grows a 5 to 25 micron oxide layer and accepts dye in black, red, blue, gold, and custom colours; this is the finish you see on consumer electronics. Type III hard anodize grows 25 to 75 microns with a Rockwell C50 surface hardness and is used for wear surfaces, hydraulic bores, and optical frames. Chromate conversion coating such as Alodine 1200 leaves an electrically conductive film that accepts paint; aerospace assemblies rely on it for bonding and EMI continuity. For exterior colour stability beyond five years, powder coat over a chromate base outperforms dyed anodize under UV.

A Taipei consumer brand moved from a two-shell ABS housing to a single-block 6061-T6 bottom case for its 14-inch notebook. The new part weighed 280 g against 410 g for the plastic twin and passed a 1.2 m drop test that the ABS version failed at 0.8 m. Cycle time on a 5-axis HSK63 machine landed at 22 minutes including a rest pass, giving a per-part cost of USD 38 at 2,500 units per week.

Tooling for the ABS version had cost USD 42,000 and needed 8 weeks. The CNC program replaced that with a 3-week NC development and USD 4,500 in fixtures, which let the brand ship two colour refreshes per year without re-tooling. Finishing was Type II black anodize on the outside and clear anodize with laser marking for the inside service label.

A survey drone maker needed a motor mount able to survive 120,000 flight cycles at 180 N peak thrust. Their original 6061-T6 part cracked at 48,000 cycles along a fillet. Redesigning in 7075-T6 and lifting the internal radius from 1.5 to 3 mm pushed fatigue life past 200,000 cycles in lab testing.

Per-part cost rose from USD 92 to USD 164 across a 1,200-unit annual run, an added USD 86,400 per year. Warranty claims on motor mounts had been running at USD 240,000 per year in field replacements and flight time, so the 7075 switch returned inside the first quarter. Surface was Type III hard anodize at 50 microns, which also isolated the mount from the carbon-fibre arm to block galvanic corrosion.

A semiconductor test-handler builder replaced a CNC-milled manifold with a DMLS-printed AlSi10Mg cooler that routed coolant along the actual heat footprint of the device under test. The printed part halved pressure drop from 1.8 to 0.9 bar at 3 L/min and dropped junction temperature 14 C at 200 W load.

Unit cost rose from USD 340 CNC to USD 620 printed, but the handler could now run two more chips per hour, a throughput gain worth USD 18 per hour of fab time. Over a 16-hour production day the cooler paid for itself in under two weeks of operation. Critical O-ring grooves were post-machined to ±0.03 mm on a 5-axis fixture.

Treat aluminum as a platform, not a single material. The gap between 5052 sheet, 6061 billet, 7075 plate, 6063 extrusion, and AlSi10Mg powder is wider than many alloys in other families, and each has a process that flatters it. Start from the mechanical and cosmetic constraint, pick the alloy and temper that meet it with the least machining drama, and let your fixture and finishing plan follow.

Done well, an aluminum assembly gives you the stiffness of a metal, the heat handling of a heat sink, and the feel of a premium consumer product at a cost closer to engineering plastic than to stainless. Done carelessly — wrong temper, wrong anodize, wrong galvanic neighbour — you inherit warranty returns that plastic would never have caused.