Material Selection Guide: Tool Steel vs Aerospace-Grade Aluminum for CNC
Featured Summary Tool steels (D2, H13) excel where wear, hardness retention at temperature and abrasion resistance dominate — typically dies, jigs and high-load fixtures. Aerospace aluminum (6061-T6, 7075-T6) wins on strength-to-weight, machinability and corrosion, making it the default for airframe brackets, EV housings and high-cycle structural components.
Choosing between a tool steel and an aerospace-grade aluminum is rarely a strength contest. It is a system-level decision involving operating temperature, cyclic loading, weight budget, surface finish, and — increasingly — total machined cost per part. This guide compares four families commonly specified for precision machined components: D2 and H13 tool steels against 6061-T6 and 7075-T6 aluminum. (Shree Lakshmi Engineering's own production materials are stainless 304/316/316L, duplex and super duplex, Inconel, mild steel, aluminium and brass — see capabilities.)
Quick comparison table
| Property | D2 Tool Steel | H13 Tool Steel | Al 6061-T6 | Al 7075-T6 |
|---|---|---|---|---|
| Tensile strength (MPa) | 1,720 | 1,420 | 310 | 572 |
| Yield strength (MPa) | 1,520 | 1,200 | 276 | 503 |
| Hardness (after HT) | 58–62 HRC | 50–54 HRC | 95 HB | 150 HB |
| Density (g/cm³) | 7.7 | 7.8 | 2.7 | 2.81 |
| Strength-to-weight | Low | Low | High | Very high |
| Machinability index | 27% | 40% | 190% | 120% |
| Service temp (°C) | ≤ 540 | ≤ 600 | ≤ 150 | ≤ 120 |
| Corrosion resistance | Poor | Poor | Excellent | Moderate |
When tool steel is the right call
Tool steels exist for one reason: they retain hardness under load, heat and abrasion. A D2 punch will outlast a 7075 punch by three orders of magnitude in a stamping die. If your component is a die, mould cavity, cutting blade, gauge, or any fixture that contacts work-hardened material under repeated impact, the answer is almost always tool steel.
D2 is air-hardening, high-carbon, high-chromium — outstanding wear resistance at room temperature. Choose D2 for cold-work tooling, blanking dies and forming punches.
H13 is hot-work tool steel, alloyed for thermal-shock resistance. Choose H13 for die-cast moulds, hot extrusion dies, plastic injection cores running glass-filled compounds, and any tool that cycles between hot metal and quench.
The penalty is machining cost. D2 and H13 in the annealed state cut at roughly one-quarter the rate of mild steel; finishing operations on hardened pieces (post-HT) require carbide or CBN tooling, slow feeds, and rigid VMC setups. Expect 2–4× the cycle time of an equivalent aluminum part.
When aerospace aluminum is the right call
If the component is a structural bracket, housing, manifold or any rotating/oscillating member where mass costs energy, aluminum dominates. Both 6061 and 7075 are precipitation-hardened (T6 = solution-treated and artificially aged), giving repeatable strength without distortion-prone heat treatment after machining.
6061-T6 is the workhorse: weldable, anodisable, corrosion-resistant, with excellent machinability and a stable supply chain. It belongs in EV battery enclosures, hydraulic manifolds, semiconductor frames, optical mounts — any part where 276 MPa yield is enough.
7075-T6 trades corrosion resistance and weldability for nearly double the yield strength of 6061. It belongs in airframe ribs, high-cycle aerospace fittings, missile bodies, and competition automotive uprights — anywhere fatigue life and stress-to-weight justify the cost premium and the protective coating that 7075 invariably needs.
Three decision rules we use on RFQs
- Operating temperature first. If the part runs above 120°C continuously, aluminum is out. Above 200°C, even most stainless steels are out — start at H13 or Inconel.
- Cyclic stress second. Aluminum has no fatigue endurance limit; every load cycle accumulates damage. For >10⁶ cycles at >25% of yield, specify 7075 with a shot-peened surface or move to 17-4 PH stainless.
- Cost-per-part last. Don't optimise material cost in isolation — a 7075 part may cost 35% more in raw stock than 6061 but machine 30% slower and require chromate conversion coating. The unit cost gap is wider than the bar-stock gap suggests.
What to send us
If you're undecided between two materials, send the load case (force, frequency, temperature, environment) along with the geometry. Our engineers benchmark across nine common alloys and recommend the lowest-cost option that meets the duty cycle — frequently saving customers 20–40% versus their initial spec.
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