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CNC machining and milling are the most popular methods for manufacturing custom parts and prototypes. The computer numerical control process has a high degree of automation and surpasses other traditional manufacturing processes in terms of production speed, efficiency and precision. Choosing the right material for a CNC machining project can seem challenging, containing many factors, including mechanical properties, cost, strength, weight, machinability, corrosion resistance, and surface finish. The machining is compatible with hundreds of metal materials, stainless steel, and aluminum being the most popular materials for custom parts and prototypes. How is aluminum machining different from steel machining? What mechanical properties do both products have? What is the degree of hardening of the material machined using CNC? We write about all this below.

Aluminum and steel – a discussion

Aluminum and stainless steel are similar in appearance and versatility, and products from these two materials can be found around us. Stainless steel is used in everything from cookware and consumer goods to construction, medical equipment, ships, and much more. Aluminum is lightweight and widely used in sports equipment, bicycles, automobiles and aerospace. So how do you differentiate between these two most popular metals? Which is better for your CNC machining project, stainless steel or aluminum milling? Today we’ll examine the difference between the two metals from different angles to help you choose a more suitable material.

Function of the materials

Aluminum is favored in consumer electronics projects because of its fine texture and versatility. Manufacturing countries are now replacing steel and plastics with this very material. Both of these materials are used to make products. If you are buying a product for long-term consumption, such as jewelry, you will need to understand the difference between these materials at some point. If you have never bought an item made of machined aluminum or steel, you won’t notice the most significant difference at first.

Stainless steel and aluminum: elemental composition and alloy properties

The elemental composition of materials is crucial for CNC machining projects, as it can significantly affect the hardness, corrosion resistance, durability and strength. Stainless steel is an iron alloy with at least 10.5% chromium, and other elements include aluminum, silicon, sulfur, nickel, selenium, molybdenum, nitrogen, titanium, copper, niobium, etc., accounting for about 0.03% -1%. The presence of chromium determines the excellent performance of stainless steel in terms of heat resistance and general corrosion resistance. The elements contained in aluminum are aluminum, silicon, zinc, magnesium, manganese, copper, iron, titanium, chromium, zirconium, etc.

Stainless steel and aluminum: corrosion resistance

Since stainless steel contains chromium, iron, nickel and other components, this means that stainless steel has excellent corrosion resistance. Chromium forms a passive protective layer on the surface, which has a self-repairing function. Aluminum has excellent corrosion resistance because it has a protective oxide layer on its surface that prevents rust and other forms of corrosion.

Stainless steel vs. aluminum: conductivity

Copper is used as a standard for conductivity. This is because it has a conductivity of 100%. Using copper as a reference for this element, it can be pointed out that aluminum conducts 61% and is lighter than it by about 30%. The conductivity of stainless steel is 3.5% that of copper, making it a poor conductor of electricity. Aluminum is ideal if electrical conductivity is a priority in a CNC machining project. In fact, aluminum is also the first choice for long-distance transmission of electricity and high-voltage cables.

Thermal conductivity

Thermal conductivity is a primary consideration for custom prototype parts or heat sinks. For this reason, aluminum is often an ideal material for air conditioners or radiators. It has a thermal conductivity of 1460 BTU-in/hr-ft²-°F (210 W/mK), making it better than stainless steel, but it has a lower melting point and softens above 400 degrees Celsius. Stainless steel is also thermally conductive, making it better suited for high-temperature work.

Material hardness

Metal hardness refers to the performance of a metal’s surface by analyzing stresses, deformations, depressions and scratches. The Brinell scale is often used as an indicator of material hardness. The hardness of stainless steel varies depending on the alloying elements. Its average on the Brinell scale ranges from 80 to 600, indicating that stainless steel has a high hardness and is difficult to form. On that scale, aluminum is determined at about 15H, which is relatively soft. Stainless steel is an ideal choice if hardness is a significant factor in a CNC machining project.

Stainless steel versus aluminum: weight

Aluminum has a density of about 2.7 g/cm3, while stainless steel has 8.0 g/cm3. The same volume of stainless steel is about three times the weight of aluminum, so aluminum comes off as a much lighter material than stainless steel. Lightweight aluminum is widely used in aircraft, ships, construction, and other applications.

Stainless steel vs. aluminum: Durability

Both stainless steel and aluminum offer excellent durability. However, the former material significantly outperforms its competitor. For this reason, stainless steel is often used to manufacture parts for cars and trucks. It is ideal if durability is a major concern in a CNC machining project.

Machinability – stainless steel or aluminum?

Material machinability refers to the ease with which milling, CNC turning, or stamping can produce custom parts or prototypes. Both stainless steel and aluminum are easier to CNC-machine. Aluminum is softer and less complicated, so CNC machining aluminum is also relatively inexpensive. Comparing the two, stainless steel is about three times harder than aluminum in CNC machining, so if ease of cutting is a major factor in a CNC machining project, aluminum is better.

Stainless steel versus aluminum in terms of plasticity

Aluminum is softer, has a lower melting point, and is easier to form than stainless steel. Steel is strong and will not warp or deform under stress, but aluminum is still the best choice if your project’s deformability is a major concern.

Stainless steel versus aluminum – the weldability aspect

Both stainless steel and aluminum are considered easy to weld, but aluminum requires more knowledge and skill, and more care must be taken when welding to avoid cracks.

Stainless steel and aluminum – yield strengths

Yield strength is the stress at which a material begins to deform permanently. Stainless steel varies from 25 MPa to 2,500 MPa depending on the alloying elements. The yield strength of aluminum alloys ranges from 7 MPa to 11 MPa. Therefore, it is much higher in stainless steel than in aluminum.

Tensile strength

The tensile strength of stainless steel is 34.5 – 3100 MPa, while that of aluminum is 90 MPa, and for some heat-treated aluminum alloys, such as aluminum 7075, the tensile strength can be increased to more than 690 MPa. It can be noted that the range in this category for stainless steel is higher than for aluminum. This means that aluminum milling is done with less tensile strength.

Shear strength

Shear strength refers to the resistance of a material to shear loads. Stainless steel ranges from 74.5 to 597 MPa, while aluminum ranges from 85 to 435 MPa, so stainless steel is a more preferred material than aluminum due to its higher shear strength.

Production costs

Stainless steel and aluminum exhibit different properties due to other alloying elements, including many types such as martensitic stainless steel, ferritic stainless steel, duplex stainless steel, austenitic stainless steel, hammer hardening, etc. In general, the CNC machining cost of stainless steel is higher than that of aluminum.


Aluminum and steel are often confused with each other. This leads people to believe that one material is better than the other, when they are very different products. Machined aluminum is a natural form of aluminum that was developed for use in aircraft and spacecraft. It is much stronger and lighter than ordinary aluminum. The most common uses for this material include producing parts for consumer electronics, including computer casings and spacecraft parts. While some consider machined aluminum to be an advancement in the steel industry, the two materials differ significantly in their properties. Stainless steel is heavier, more durable but more difficult to machine. While both products are great, each should be used for a specific job because of its characteristics. Proper chip removal and a large acceptable linear expansion coefficient are also important when working on stainless steel, machining copper, or stainless steel. Our company provides milling services to help with machine building or aluminum machining.