Materials

6061 vs. 7075 vs. MIC-6: Choosing Aluminum for Machined Parts

LightsOut CNC Journal · 6 min read

Most machined aluminum parts are made from one of three materials: 6061, 7075, or MIC-6 cast plate. They look the same on the rack. They behave very differently in use. Picking the wrong one can mean a part that is too weak, too hard to finish, or one that warps after machining. This guide explains each one in simple terms and when to use it.

Quick answer. Use 6061-T6 as your default. It is strong enough for most parts, welds well, and anodizes well. Use 7075-T6/T651 when you need high strength and low weight, like aerospace brackets and fittings. Use MIC-6 when flatness and stability matter more than strength, like fixtures, jigs, and base plates.

1. The three materials at a glance

What it is: 6061 — rolled or extruded alloy with magnesium and silicon. 7075 — rolled alloy with zinc as the main addition. MIC-6 — cast, stress-relieved tooling plate.
Tensile strength (typical): 6061-T6 — about 45 ksi (310 MPa). 7075-T651 — about 83 ksi (572 MPa). MIC-6 — about 24 ksi (166 MPa).
Yield strength (typical): 6061-T6 — about 40 ksi (276 MPa). 7075-T651 — about 73 ksi (503 MPa). MIC-6 — about 15 ksi (105 MPa).
Welding: 6061 — good, but the weld area loses some strength. 7075 — generally not welded. MIC-6 — not recommended by most sources.
Anodizing: 6061 — good. 7075 — fair to good. MIC-6 — hard to get an even look.
Corrosion resistance: 6061 — good. 7075 — lower than 6061. MIC-6 — rated poor by tooling-plate makers.
Best for: 6061 — general parts, housings, enclosures. 7075 — high-strength, weight-critical parts. MIC-6 — fixtures, jigs, base plates, flat surfaces.

Strength values are typical published numbers for plate. Actual values depend on thickness, temper, and the spec on your drawing. "ksi" means thousands of pounds per square inch.

2. 6061-T6: the everyday choice

6061 is one of the most popular aluminum alloys. It has a good mix of strength, machinability, weldability, and corrosion resistance. The "T6" means it was heat-treated and aged for strength.

Pick it when: the part needs decent strength, may be welded, or needs a clean anodized finish.
Watch out for: welding lowers strength near the weld. If a welded part must carry load, plan for that.
Common uses: enclosures, housings, brackets, plates, and general hardware.

3. 7075-T6 / T651: when strength matters

7075 is one of the strongest common aluminum alloys. In the T6 condition, its tensile strength is close to double that of 6061-T6. That is why it shows up in aircraft structures and other parts where weight counts.

Pick it when: the part is highly loaded and you want to keep weight down.
T651 vs. T6: T651 plate is stretched after heat treatment to relieve stress. That helps parts stay straighter as material is cut away.
T73 temper: an over-aged version with a bit less strength but much better resistance to stress corrosion cracking. Some aerospace drawings call for it.
Watch out for: 7075 is generally not welded, and its corrosion resistance is lower than 6061. Plan on anodizing or another coating for most uses.

4. MIC-6: when flatness matters

MIC-6 is a cast aluminum tooling plate first developed by Alcoa (MIC-6 is a registered trademark). Unlike rolled plate, it is cast and stress-relieved, so it has very little built-up stress inside. That means it stays flat when you cut deep pockets into it.

Flatness from the mill: published tolerances are within 0.015" on 1/4"–5/8" thick plate and 0.005" on 3/4"–4" thick plate.
Thickness and finish: about ±0.005" thickness tolerance, with both faces machined to about 20 microinches.
Pick it when: you need a flat, stable base: fixtures, jigs, gauge plates, vacuum chucks, and machine bases.
Watch out for: it is much weaker than 6061-T6 and stretches only about 3% before breaking. Do not use it for structural or safety-critical parts. It is also soft (about 65 Brinell), so locating holes may need steel bushings.
Finishing: anodizing MIC-6 can look uneven because of its cast grain. If looks matter, ask about a sample first.

5. A quick way to choose

Does the part carry high loads, and does weight matter? Start with 7075.
Does it need to be welded? Use 6061.
Is flatness the main job, with low loads? Use MIC-6.
None of the above? 6061-T6 is usually the safe default.
Does your drawing or customer spec name an alloy and temper? Follow the drawing. Do not substitute without written approval.

A note on cost. Material prices and stock sizes change often. If you are open to more than one alloy, ask your shop to quote both. The machining time can differ as much as the material price.

6. What to put on your drawing

Alloy and temper (for example, 6061-T6 or 7075-T651).
Material spec, if your customer requires one (for example, an AMS or ASTM spec number).
Whether you need material certifications with the parts.
Finish: anodize type and class, color, and any masking.

Frequently asked questions

Is 7075 stronger than 6061? Yes. In the T6 condition, 7075 has close to double the tensile strength of 6061.

Can you weld 7075 aluminum? It is generally not welded with normal fusion welding. If a part needs welding, 6061 is the usual choice.

What is MIC-6 used for? Fixtures, jigs, base plates, and other parts where flatness and stability matter more than strength.

Is MIC-6 strong? No. Its typical tensile strength is about 24 ksi, roughly half that of 6061-T6, and it is brittle. It is not meant for structural parts.

What is the difference between T6 and T651? T651 is T6 material that was stretched to relieve internal stress. It tends to stay straighter during machining.

About the author

Andrew Adams is the founder and CEO of LightsOut CNC, an automated 5-axis machine shop opening in November 2026 in the Los Angeles South Bay, set up to machine 6061, 7075, 2024-T3, and MIC-6 aluminum. See our capabilities or upload a part for a quote.

More about Andrew and his other articles →

This article is for general information and entertainment purposes only. It is not engineering advice. Always follow your drawing and your customer's material specs.