Metal Material Selection Guide: How to Choose the Right Alloy for CNC Machining

Introduction

Selecting the right metal alloy for CNC machining is one of the most consequential decisions in precision manufacturing. The material you choose determines not only the mechanical performance of the final part — its strength, hardness, wear resistance, and fatigue life — but also how efficiently it can be machined, what surface finish is achievable, and ultimately, the cost per part.

With over 50 material grades available through MetalBizz, engineers face a complex decision matrix. Aluminum alloys offer excellent machinability and light weight. Steels provide unmatched strength and wear resistance. Titanium delivers exceptional strength-to-weight ratios for demanding applications. Brass and copper bring superior electrical and thermal conductivity. This guide provides mechanical properties data, machinability ratings, and application guidance for each family, helping you make an informed material selection for your CNC machining project.

Aluminum Alloys

Aluminum is the most commonly machined metal across all industries — from aerospace to automotive to consumer electronics. Its combination of light weight (2.7 g/cm³), good corrosion resistance, and excellent machinability makes it the default choice for a wide range of applications. The two most widely used grades are 6061 and 7075.

**6061 Aluminum** is the general-purpose workhorse. It offers good strength (tensile yield 276 MPa), excellent corrosion resistance, good weldability, and very good machinability. It is heat-treatable to the T6 temper, which maximizes its mechanical properties while maintaining reasonable cost. Typical applications include structural frames, automotive components, marine hardware, and consumer electronics enclosures.

**7075 Aluminum** is the high-strength option, with a tensile yield strength of 503 MPa in the T6 temper — approaching some low-grade steels. It is the preferred material for aerospace structural components, high-performance bicycle frames, and molds. However, its machinability is slightly inferior to 6061, and it has lower corrosion resistance, often requiring protective coatings.

**2024 Aluminum** offers high strength and excellent fatigue resistance, commonly used in aircraft wing structures. Its machinability is good but not as consistent as 6061.

Grade │ Tensile Yield (MPa) │ Ultimate Tensile (MPa) │ Hardness (HB) │ Machinability Rating │ Density (g/cm³) │ Typical Applications

|-------|--------------------|----------------------|--------------|---------------------|----------------|---------------------|

6061-T6 │ 276 │ 310 │ 95 │ Excellent (90%) │ 2.70 │ Structural frames, automotive, marine

7075-T6 │ 503 │ 572 │ 150 │ Good (70%) │ 2.81 │ Aerospace, high-performance, molds

2024-T3 │ 345 │ 469 │ 120 │ Good (70%) │ 2.78 │ Aircraft structures, military

5052-H32 │ 193 │ 228 │ 60 │ Very Good (80%) │ 2.68 │ Sheet metal, tanks, marine

5083-H116 │ 228 │ 317 │ 89 │ Good (65%) │ 2.66 │ Shipbuilding, pressure vessels

Machinability ratings are relative to 6061-T6 (100% baseline).

Steel Grades

Steel remains the backbone of industrial manufacturing, offering the broadest range of strength, hardness, and wear resistance among common machined metals. Carbon steels, alloy steels, and stainless steels each fill distinct roles.

**1215 Carbon Steel** is the most machinable steel grade, containing lead or sulfur additives that create chip-breaking inclusions. It achieves machinability ratings of 80–90% relative to 6061 aluminum, making it ideal for high-volume turned parts. However, its strength is limited (tensile yield 415 MPa), and it lacks corrosion resistance.

**4140 Alloy Steel** is the most popular general-purpose steel for CNC machining. It offers excellent strength (tensile yield 655 MPa in the quenched-and-tempered condition), good toughness, and moderate machinability (65–70%). It is widely used for shafts, gears, axles, structural components, and tooling. Pre-hardened 4140 (28–32 HRC) arrives at the machine ready to use without post-machining heat treatment.

**304 Stainless Steel** is the most common austenitic stainless steel, combining good corrosion resistance with moderate strength. It work-hardens rapidly during machining, requiring rigid setups and sharp tooling. Its machinability is rated at 45–50%, significantly lower than carbon steels. Applications include food processing equipment, chemical tank fittings, and architectural hardware.

**316 Stainless Steel** adds molybdenum for improved corrosion resistance, especially against chlorides and marine environments. Its machinability is similar to 304 (40–45%), but it is more prone to work hardening. It is the standard for marine components, pharmaceutical equipment, and chemical processing.

Grade │ Tensile Yield (MPa) │ Ultimate Tensile (MPa) │ Hardness (HRC / HB) │ Machinability Rating │ Typical Applications

|-------|--------------------|----------------------|--------------------|---------------------|---------------------|

1215 │ 415 │ 540 │ 179 HB │ Very good (85%) │ High-volume turned parts, fittings

4140 (Q&T) │ 655 │ 1020 │ 28–32 HRC │ Good (65%) │ Shafts, gears, axles, tooling

1018 │ 310 │ 440 │ 126 HB │ Good (70%) │ Structural parts, low-stress components

304 SS │ 215 │ 505 │ 201 HB │ Fair (45%) │ Food equipment, chemical fittings

316 SS │ 290 │ 579 │ 217 HB │ Fair (40%) │ Marine components, medical devices

Titanium Alloys

Titanium alloys offer the highest strength-to-weight ratio among common structural metals, combined with exceptional corrosion resistance and biocompatibility. Grade 5 (Ti-6Al-4V) accounts for approximately 50% of all titanium used worldwide.

**Ti-6Al-4V (Grade 5)** has a tensile yield strength of 880 MPa at a density of just 4.43 g/cm³ — a strength-to-weight ratio roughly double that of 304 stainless steel. It maintains strength up to 400°C and is virtually inert in the human body, making it the standard for aerospace structural components and medical implants. However, it is notoriously difficult to machine, with a machinability rating of only 20–25%. Titanium's low thermal conductivity traps heat at the cutting edge, accelerating tool wear. Successful machining requires low cutting speeds, high pressure coolant, and sharp carbide or PCD tooling.

**Grade 2 (Commercially Pure Titanium)** offers lower strength (tensile yield 345 MPa) but superior corrosion resistance and formability. It is easier to machine than Grade 5 but still challenging compared to aluminum or steel. Common applications include chemical processing equipment, heat exchangers, and marine components.

Grade │ Tensile Yield (MPa) │ Ultimate Tensile (MPa) │ Hardness (HRC) │ Machinability Rating │ Density (g/cm³) │ Typical Applications

|-------|--------------------|----------------------|---------------|---------------------|----------------|---------------------|

Ti-6Al-4V (Grade 5) │ 880 │ 950 │ 36 │ Poor (20%) │ 4.43 │ Aerospace, medical implants

Grade 2 (CP) │ 345 │ 483 │ 80 HB │ Fair (30%) │ 4.51 │ Chemical processing, marine

Ti-6Al-4V ELI (Grade 23) │ 830 │ 900 │ 34 │ Poor (20%) │ 4.43 │ Surgical implants, cryogenic

Brass Alloys

Brass is an alloy of copper and zinc, prized for its excellent machinability, corrosion resistance, and attractive gold-like appearance. It is the fastest-machining common metal, with machinability ratings of 100–150% relative to 6061 aluminum.

**C36000 (Free-Cutting Brass)** is the standard for high-speed CNC turning. Its lead content creates short, broken chips that evacuate easily, allowing cutting speeds of 400–600 m/min with excellent surface finishes as low as Ra 0.4μm. Tensile yield strength is 310 MPa. It is used for fittings, valves, electrical connectors, decorative hardware, and plumbing components. Note that RoHS regulations restrict lead content in some markets — lead-free alternatives such as C69300 are available.

**C46400 (Naval Brass)** adds tin for improved corrosion resistance in marine environments. It has good strength (tensile yield 240 MPa) and good machinability (80%). It is used for marine hardware, propeller shafts, and condenser plates.

Grade │ Tensile Yield (MPa) │ Ultimate Tensile (MPa) │ Hardness (HB) │ Machinability Rating │ Density (g/cm³) │ Typical Applications

|-------|--------------------|----------------------|--------------|---------------------|----------------|---------------------|

C36000 │ 310 │ 448 │ 100 │ Excellent (150%) │ 8.50 │ Fittings, valves, connectors

C46400 │ 240 │ 400 │ 95 │ Good (80%) │ 8.41 │ Marine hardware, shafts

C26000 │ 200 │ 380 │ 82 │ Good (70%) │ 8.53 │ Decorative, architectural, musical

Copper Alloys

Copper and its alloys are specified primarily for their outstanding electrical and thermal conductivity. Pure copper (C11000) has the highest conductivity of any common machined metal — 100% IACS (International Annealed Copper Standard) — with a thermal conductivity of 401 W/m·K, roughly 20× that of titanium and 4× that of steel.

**C11000 (Electrolytic Tough Pitch Copper)** is the standard pure copper grade. It machines well with sharp tooling but produces long, stringy chips that require chip-breaking features. Tensile yield is 200 MPa. Applications include bus bars, electrical connectors, heat sinks, and RF components.

**C17200 (Beryllium Copper)** combines high strength (tensile yield 1140 MPa in the hardened condition — comparable to tool steel) with good conductivity (22–25% IACS). It is the material of choice for springs, electrical contacts, molds, and down-hole tools. It commands a significant cost premium and requires proper ventilation during machining due to beryllium content.

**C14500 (Tellurium Copper)** is a free-machining alternative to pure copper, with sulfur or tellurium additions that improve chip breakage. It retains 90–95% of pure copper's conductivity with significantly better machinability.

Grade │ Tensile Yield (MPa) │ Ultimate Tensile (MPa) │ Hardness (HB) │ Machinability Rating │ Conductivity (% IACS) │ Typical Applications

|-------|--------------------|----------------------|--------------|---------------------|----------------------|---------------------|

C11000 │ 200 │ 379 │ 80 │ Fair (40%) │ 100% │ Bus bars, heat sinks, electrical

C17200 │ 1140 (HT) │ 1250 (HT) │ 40 HRC │ Fair (40%) │ 22–25% │ Springs, contacts, molds

C14500 │ 220 │ 345 │ 75 │ Good (70%) │ 90–95% │ Electrical components, fittings

How to Choose the Right Material

Material selection is a multi-variable engineering trade-off. The optimal choice depends on the specific requirements of your application across several dimensions:

Strength requirements:: For parts bearing static or cyclic loads, compare yield strength and fatigue limits. Steel (4140 Q&T at 655 MPa) and titanium (Grade 5 at 880 MPa) lead in strength. Aluminum 7075 (503 MPa) is a strong lightweight alternative.

Weight constraints:: When every gram matters — aerospace, automotive, robotics — aluminum (2.7 g/cm³) and titanium (4.4 g/cm³) are the clear choices over steel (7.8 g/cm³) and brass/copper (8.5 g/cm³).

Corrosion environment:: Marine and chemical processing applications demand stainless steel (316), titanium (Grade 2), or properly anodized aluminum. Carbon steels and plain brass require protective coatings in corrosive environments.

Electrical/thermal needs:: Copper (100% IACS) is unmatched for electrical conductivity. Brass (26% IACS) is a good machinable alternative. Aluminum (61% IACS) provides good conductivity at lower weight.

Machinability and cost:: Brass C36000 machines fastest, followed by aluminum 6061. Steel 1215 is the most machinable steel. Titanium and stainless steel (304/316) are the most expensive to machine due to slow cutting speeds and accelerated tool wear.

Surface finish requirements:: Aluminum 6061, brass, and 1215 steel achieve the finest as-machined surface finishes (Ra 0.4–0.8μm). Titanium and stainless steel typically require secondary operations for fine finishes.

Budget:: Per-part material cost varies significantly. Aluminum is generally the most cost-effective. Steel is moderate. Brass is 2–3× more expensive. Titanium and beryllium copper are the most expensive materials to machine.

Material Properties Comparison Table

Property │ Aluminum 6061-T6 │ Steel 4140 Q&T │ Ti-6Al-4V │ Brass C36000 │ Copper C11000

|----------|-----------------|---------------|-----------|-------------|--------------|

Density (g/cm³) │ 2.70 │ 7.85 │ 4.43 │ 8.50 │ 8.92

Tensile Yield (MPa) │ 276 │ 655 │ 880 │ 310 │ 200

Ultimate Tensile (MPa) │ 310 │ 1020 │ 950 │ 448 │ 379

Elongation at Break (%) │ 12 │ 22 │ 14 │ 25 │ 45

Hardness │ 95 HB │ 28–32 HRC │ 36 HRC │ 100 HB │ 80 HB

Machinability Rating │ 100% (baseline) │ 65% │ 20% │ 150% │ 40%

Thermal Cond. (W/m·K) │ 167 │ 42.6 │ 6.7 │ 120 │ 401

Electrical Cond. (% IACS) │ 43 │ 3 │ 1 │ 26 │ 100

Melting Point (°C) │ 585–652 │ 1416 │ 1604–1660 │ 900–940 │ 1083

Relative Material Cost │ $ │ $$ │ $$$$ │ $$$ │ $$

Relative Machining Cost │ $ │ $$ │ $$$$$ │ $ │ $$

FAQ

What is the easiest metal to CNC machine?

Brass C36000 (free-cutting brass) is widely regarded as the easiest metal to machine, with machinability rated at 150% of 6061 aluminum. It produces short, broken chips, allows high cutting speeds (400–600 m/min), and achieves excellent surface finishes. Aluminum 6061 and steel 1215 are also excellent choices for easy machining.

What is the strongest metal alloy for CNC machining?

For common machined alloys, beryllium copper C17200 in the hardened condition achieves tensile yield strength of 1140 MPa — comparable to tool steel. Among structural materials, Ti-6Al-4V (tensile yield 880 MPa) and 4140 alloy steel (655 MPa quenched-and-tempered) are the most widely used high-strength options. For maximum strength, consider tool steels such as A2 or D2 (1800–2000 MPa) though these require specialized machining.

Can aluminum and stainless steel be machined on the same CNC machine?

Yes, but with important caveats. Stainless steel work-hardens and can leave embedded work-hardened particles on the machine table and in coolant, which can then cause galling on softer aluminum parts machined subsequently. Best practice is to machine aluminum first, then stainless steel, with thorough cleaning of the work zone and coolant between material changes. Some shops maintain dedicated machines for stainless steel.

How do I choose between 6061 and 7075 aluminum?

Choose 6061-T6 when you need good strength, excellent corrosion resistance, very good machinability, and lower cost — suitable for 80% of general applications. Choose 7075-T6 when you need approximately 80% higher yield strength (503 MPa vs 276 MPa) and the part will not be exposed to corrosive environments without protective coating. 7075 is approximately 30–50% more expensive and slightly harder to machine.

Does material choice affect CNC machining lead time?

Significantly. Aluminum 6061 and brass can be machined at 2–4× the cutting speeds of stainless steel and titanium. A simple part that takes 15 minutes in aluminum may require 45–60 minutes in 316 stainless steel and 60–90 minutes in Ti-6Al-4V. This directly extends lead time and increases cost. Always consider material machinability when planning project timelines.

Conclusion

Material selection is the foundation of successful CNC machining projects. Aluminum 6061-T6 remains the best all-around choice for most applications, offering the optimal balance of strength, weight, machinability, and cost. When higher strength is needed, 4140 alloy steel or 7075 aluminum provide excellent options. For extreme strength-to-weight and biocompatibility, titanium Ti-6Al-4V is unmatched. Brass and copper serve specialized roles where conductivity or rapid machinability is paramount.

MetalBizz offers over 50 material grades for CNC machining, supported by in-house material stock and engineering expertise. Our team provides DFM feedback within 24 hours, including material recommendations tailored to your specific application. Upload your CAD files or visit our Materials page to explore the full catalog.

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