Metal Materials for Machining: 24 Common Grades and How They Cut
This page covers 24 metal materials for machining, grouped by family, with the cutting behavior, typical parts and limits of each. It is written for design engineers and buyers who specify stock, not for a materials textbook. Read it and you can pick a grade on the drawing before you send an RFQ.
What Machinability Measures in Metal Materials
Machinability is not one number. It is a mix of cutting speed the tool can survive, chip shape, tool wear rate, surface finish left behind, and how much the part moves after the vise is released. Two shops can run the same bar and report different results because spindle rigidity and coolant delivery change the picture.
The common 100% baseline is AISI 1018 low-carbon steel. A grade rated 200% machines twice as fast under the same setup and tool. Free-machining stainless 303 sits high on that scale. Titanium grade 5 (Ti-6Al-4V) sits far lower, and heat-resistant alloys like Inconel sit lower still.
That rating is a starting point, not a promise. A 200% grade on a worn spindle can finish worse than a 60% grade on a rigid 5-axis center. When we quote metal materials for machining, we look at the feature first: thin walls, deep pockets and tight true position all punish a grade more than its rating suggests.
Chip control is the second signal. Aluminum 6061 breaks clean and clears fast. 304 stainless work-hardens at the cut and forms a stringy chip that wraps the tool. Copper alloys gum. If your part has deep bores or small internal radii, chip evacuation decides the cycle time more than the material spec does.
Heat is the third. Titanium and Inconel push cutting temperature into the tool coating instead of the chip, so cutters fail by cratering rather than flank wear. Coolant through the tool and lower surface speed keep the edge alive.
Aluminum Alloys: 6061, 7075, 2024 and Cast Grades
Aluminum is the default for machined housings, brackets and fixtures. 6061-T6 is the workhorse: good strength, weldable, anodizes cleanly, and cuts at high surface speed with sharp carbide. Most 5-axis brackets we run start here.
7075-T6 gives roughly twice the yield strength of 6061 and machines almost as well. It is the choice for aerospace ribs and load-bearing arms. The trade-off is corrosion resistance and weldability; 7075 does not like anodizing in thin sections and should not be welded.
2024-T4 machines well and is common in aircraft structure, but it is even less corrosion resistant. 5052 and 5083 are marine and sheet grades, softer and gummy to cut, better formed than machined. 6063 and 6082 are extrusion and European structural grades with predictable properties.
ADC12 is a die-casting alloy, not a bar stock. It appears in covers and housings where porosity is acceptable. If you need pressure tightness or thin walls under 1 mm, billet 6061 is the safer route.
Stainless Steels and Carbon Steels Compared
Stainless 303 is the free-machining grade. Sulfur additions break the chip and let a shop run 30-50% faster than 304. It is right for shafts, bushings and fittings that will not be welded. The sulfur also lowers corrosion resistance and makes welds crack, so 303 is a poor choice for a welded manifold.
304 and 316 are the general corrosion grades. 316L adds molybdenum and low carbon for chloride service and welded assemblies, including medical and food-contact parts. Both work-harden, so light passes with a positive rake insert beat heavy cuts that rub the surface.
17-4PH (SUS630) is a precipitation-hardening stainless. It machines at condition A around 30 HRC, then ages to roughly 40 HRC. It suits valve bodies and pump shafts where 316 is too soft but 440C is too brittle.
On the carbon side, 1018 is the baseline, 1045 turns into shafts and gears, and 4130, 4140 and 4340 are the chromoly grades for stressed parts. 4140 at 28-32 HRC is a common pre-hardened mold and tooling stock. A36 is structural plate, cheap and easy to cut but not for tight tolerance work.
Tool steel (A2, D2, H13) machines annealed and then hardens. Cut it before heat treat, leave grinding stock, and plan for 0.2-0.5 mm of distortion on a long part.
Copper Alloys, Titanium and Heat-Resistant Grades
Copper and brass cut easily but grab the tool. C36000 free-cutting brass is the fastest of the group and suits fittings and connectors. C101 and C110 are high-conductivity coppers for busbars and heat sinks; they are soft, so deburring matters more than tolerance. C27400 and C28000 cover the higher-strength brass range.
Beryllium copper is a different animal. It machines to good strength and spring properties but the dust is toxic, so it needs controlled coolant and chip handling. Use it only when conductivity and spring temper are both required.
Titanium TA1 and TA2 are commercially pure and comparatively forgiving. TC4 (Ti-6Al-4V) is the structural grade: strong, light, and slow to cut. It conducts heat poorly, so the edge takes the temperature. Expect reduced tool life, no free lunch on surface speed, and a strong case for 5-axis so you can keep the cutter engaged in one pass.
Inconel and similar nickel alloys are the hardest of the 24 to machine. They work-harden and hold heat. They belong in exhaust, turbine and high-temperature fixtures, and they justify the cycle time only when nothing else survives the service temperature.
Magnesium AZ31B and AZ91D cut fast and light, but the chips are flammable. They need dedicated handling and a shop that already runs magnesium. We machine them only with the fire controls in place.
Metal Materials for Machining: Selection Table
Ratings are relative within this table.
| Grade | Best for | Main limit |
|---|---|---|
| 6061-T6 aluminum | Housings, brackets, fixtures | Moderate strength, wears at contact points |
| 7075-T6 aluminum | Aerospace ribs, loaded arms | Poor weldability, corrosion in thin sections |
| 2024-T4 aluminum | Aircraft structure | Low corrosion resistance, needs coating |
| 303 stainless | Shafts, bushings, fittings | Not weldable, lower corrosion resistance |
| 304 / 316L stainless | Food, medical, welded assemblies | Work-hardens, stringy chips, slow |
| 17-4PH stainless | Valve bodies, pump shafts | Needs aging cycle after machining |
| 4140 steel (28-32 HRC) | Molds, tooling, stressed shafts | Pre-hardened stock, slower than 1018 |
| C36000 brass | Fittings, connectors | Gums on deep bores without coolant |
| TC4 titanium | Structural aerospace parts | Very low cutting speed, short tool life |
| Inconel | Exhaust, turbine, high-temp fixtures | Work-hardens, highest cost per cut |
How to Decide
If the part is a housing or bracket, start at 6061-T6 and only move up when strength or temperature demands it. If it must survive chloride, steam or a weld, choose 316L over 303 and accept the slower cycle. If it flies, pick 7075 or TC4 and budget for tool life.
Questions Engineers Ask
Can I substitute 6061 for 7075 without telling the shop?
Not safely. 7075-T6 is roughly twice the yield strength of 6061-T6, so a thinner section may pass in 6061 on paper and still deflect in service.
Tell the shop which property matters. If it is stiffness, geometry changes more than grade. If it is yield, the grade is the point.
Why does 304 stainless cost more to machine than 303?
303 contains sulfur, which breaks the chip and lets the tool run faster with less rubbing. 304 work-hardens under the cut, so a heavy pass that rubs hardens the next pass.
The difference shows up in cycle time and tool changes, not in the bar price. On a deep bore, 303 can cut the machining cost by a third.
When is titanium worth the cost?
When weight and corrosion resistance both matter, or when the service temperature rules out aluminum. TC4 keeps strength to roughly 400 °C in many applications.
If the part is a static bracket at room temperature, aluminum does the same job for less. Titanium earns its price on loaded, hot or aggressive parts.
Does hardness decide the tolerance I can hold?
Partly. Soft grades like C110 copper and 5052 deflect under clamping and cutting pressure, so the finished part can spring back after unclamping. Harder grades hold form better.
For tight work, we rough, stress-relieve where the alloy allows, then finish in a light pass. That is how ±0.005 mm stays repeatable on thin walls.
What surface finish can I expect from each family?
Aluminum and brass reach Ra 0.8-1.6 μm with normal finishing passes, and Ra 0.2-0.8 μm with a dedicated fine pass.
Stainless and titanium sit one band rougher for the same setup. If the drawing calls for a mirror finish on 316L, plan for extra polishing time.
Can one shop run all 24 grades?
Only with the right tooling and coolant. Aluminum wants high speed and sharp edges; Inconel wants low speed, rigid holders and through-tool coolant.
Ask which grades the shop runs weekly. The answer tells you more than a capability list.
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