Stainless steel vs aluminum, which is better for your CNC machining project

CNC machining is one of the most common manufacturing methods for custom parts and prototypes. The process of computer numerical control is highly automated and is superior to other traditional manufacturing processes in terms of speed, production efficiency, and precision. But choosing the right material for your CNC machining project also seem challenging, with many factors to consider, which include mechanical properties, cost, strength, weight, machinability, corrosion resistance, and surface finish.

CNC machining is compatible with hundreds of metal materials, of which stainless steel and aluminum are the most popular for custom parts and prototypes. Aluminium and stainless steel have similar looks, both are versatile, and products made of both materials are always found around us. Applications of stainless steel range from cookware and consumer goods to construction, and even ships, medical devices, and more. Aluminum is light in weight and is widely used in sporting goods, bicycles, automobiles, and aerospace. So how do we differentiate between the two most popular metal materials? Stainless steel vs aluminum, which is better for your CNC machining project? Today we analyze the difference between the two metals from various aspects to help you choose a more suitable material.

Stainless steel vs aluminum

Stainless steel vs aluminum:Elemental composition

The elemental composition of a material is critical to CNC machining projects, as the composition of the metal has a large impact on hardness, corrosion resistance, durability, and strength. Stainless steel is an iron alloy containing at least 10.5% chromium, and other elements include aluminum, silicon, sulfur, nickel, selenium, molybdenum, nitrogen, titanium, copper and niobium, accounting for about 0.03%-1%. The presence of chromium determines the excellent properties of stainless steel in terms of heat resistance and corrosion resistance. Other elements that aluminum contains include: aluminum, silicon, zinc, magnesium, manganese, copper, iron, titanium, chromium, zirconium, and more.

Composition of Major Stainless Steel Alloys

Alloy Grades

%C

%Mn

%P

%S

%Si

%Cr

%Ni

%Mo

SS304

0.040

1.580

0.024

0.040

0.400

18.35

8.040

0.070

SS304L

0.010

1.638

0.023

0.002

0.412

18.56

8.138

0.364

SS316

0.080

2.000

0.045

0.030

1.000

16.80

11.20

2.500

SS316L

0.020

1.390

0.024

0.080

0.480

16.80

10.22

2.080

Composition of Major Aluminum Alloys

Alloy

%Cu

%Mg

%Mn

%Si

%Zn

2024

4.4

1.5

0.6

0

0

6061

0

1

0

0.6

0

7005

0

1.4

0

0

4.5

7075

1.6

2.5

0

0

5.6

356.0

0

0.3

0

7

0

Stainless steel vs aluminum anodizing

Stainless steel vs aluminum:Corrosion resistance

Because stainless steel contains chromium, iron and nickel components, which determines that stainless steel has excellent corrosion resistance. Chromium forms a passivating protective layer on the surface of stainless steel and has a self-healing function. The reason for aluminum’s excellent corrosion resistance is that it has a protective oxide layer on its surface that prevents it from rusting and prevent it from other forms of corrosion.

Stainless steel vs aluminum:Electrical conductivity

Copper, as the standard for electrical conductivity, has a conductivity of 100%. Using copper as a reference, aluminum has a conductivity of 61% and is about 30% lighter than copper. The conductivity of stainless steel is 3.5% of that of copper, making it a poor conductor of electricity. Aluminum is the ideal material if conductivity is the first element for your CNC machining project. In fact, aluminum is also the first choice for carrying electricity and high-voltage wires over long distances.

Stainless steel vs aluminum:Thermal conductivity

Thermal conductivity is the first consideration for custom parts or prototypes for heat sinks. This is why aluminum is often the ideal material for air conditioning units or radiators.Aluminum has a thermal conductivity of 1460 BTU-in/hr-ft²-°F (210 W/mK), which is better than stainless steel, but aluminum has a lower melting point and softens or even melts above 400 degrees Celsius, losing its properties. Stainless steel is also thermally conductive, making it better for working at high temperatures.

Stainless steel vs aluminum:Melting point

The melting point of the material is very important for CNC machining projects. Parts operate at high temperatures, and if they reach their melting point, they will transform from solid to liquid and lose function. With a lower melting point, the material is more suitable for die casting or extrusion. The melting point of stainless steel varies depending on the alloying elements and is approximately between 1230 °C and 1530 °C. Aluminum has a relatively low melting point, around 660.37 °C. This means that if heat resistance is a primary consideration for your CNC machining project, stainless steel is preferable to aluminum.

Stainless steel vs aluminum:Hardness

The hardness of metal refers to the stress performance of etching, deformation, depression and scratches on the metal surface. Brinell hardness is usually used as an indicator of material hardness. Stainless steel varies with alloying elements. The average Brinell hardness is between 80 and 600, which indicates that stainless steel has high hardness and is difficult to form. The Brinell hardness of aluminum is around 15H, which is relatively soft. Stainless steel is ideal if hardness is the primary consideration for your CNC machining project.

Stainless steel vs aluminum:Weight

Aluminum has a density of approximately 2.7 g/cm 3 , while stainless steel has a density of 8.0 g/cm 3 . The same volume of stainless steel is about three times the weight of aluminum, so aluminum is much lighter than stainless steel. Lightweight aluminum is widely used in aircraft, ships, construction and other fields.

Stainless steel vs aluminum:Durability

Both stainless steel and aluminum have excellent durability, and there is no doubt that stainless steel is harder and stronger than aluminum. That’s why stainless steel is often used to make truck and auto parts. Stainless steel is ideal if durability is a primary consideration for your CNC machining project.

Stainless steel vs aluminum:Processability

The machinability of a material refers to how easily a custom part or prototype can be manufactured through CNC milling, CNC turning or stamping. Both stainless steel and aluminum are easier to CNC machine. Aluminum is softer and less rigid, so CNC machining aluminum is also relatively inexpensive. Comparing the two kind of material, CNC machining stainless steel is about three times as difficult as aluminum.

Stainless steel vs aluminum:Formability

Compared to stainless steel, aluminum is softer, has a lower melting point, and is easier to form. Stainless steel is strong and will not warp or deform under force, but if formability is a primary consideration for your project, aluminum is still the best choice.

Stainless steel vs aluminum:Solderability

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

Stainless steel vs aluminum:Yield strength

Yield strength refers to the stress at which a material begins to deform permanently. The yield strength of stainless steel varies depending on the alloying elements, from 25 MPa to 2500 MPa. The yield strength of aluminum alloys ranges from 7 MPa to 11 MPa. Therefore, the yield strength of stainless steel is much higher than that of aluminum.

Stainless steel vs aluminum:Tensile strength

Stainless steel has a tensile strength of 34.5 – 3100 MPa, while aluminum has a tensile strength of 90 MPa, and for some heat treatable aluminum alloys, such as aluminum 7075, the tensile strength can be increased to over 690 MPa. It can be seen that the tensile strength of stainless steel is much higher than that of aluminum.

Stainless steel vs aluminum:Shear strength

Shear strength refers to the resistance of a material to shear loads. The shear strength of stainless steel is between 74.5 – 597 MPa, while that of aluminum is between 85 and 435 MPa. The shear strength of stainless steel is stronger than that of aluminum.

Stainless steel vs aluminum:Cost

Stainless steel and aluminum exhibit different properties due to different alloying elements, including many many different types, such as martensitic stainless steel, ferritic stainless steel, duplex stainless steel, austenitic stainless steel, precipitation hardening stainless steel, etc., while the aluminum type There are 1-9 series. In general, CNC machining stainless steel costs more than aluminum.

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Stainless steel vs aluminum:Scope of application

Stainless steel304, 316 and other austenitic stainless steels are most popular due to their excellent balance of strength, corrosion resistance and cost. Grades 430 and 434 are popular ferritic stainless steels, while grade 420 stainless steel (usually in annealed form) is a popular choice for martensitic stainless steels. Applications of stainless steel include aerospace, agriculture, construction, automotive, construction, electronics, food service, household appliances, manufacturing, marine, medical, oil and gas, pharmaceutical, power generation, pulp and paper, sports equipment and other industries.

Aluminum:The most popular aluminum models include 2024, 5052, 6061, 6063 and 7075, of which aluminum 5052 has excellent seawater corrosion resistance and is the first choice for the manufacture of marine parts. Applications of aluminum include aerospace, medical, automotive, chemical processing, heat dissipation components, electronic products, marine engineering, power systems, etc.

Summarize

  • Aluminum is known for its rust resistance, light weight, and general corrosion resistance and strength.

  • Stainless steel has excellent corrosion resistance and tensile strength, and its weight is about three times that of aluminum.

  • Stainless steel has excellent heat resistance, while aluminum has excellent thermal conductivity, but aluminum cannot withstand high temperature applications due to its melting point.

  • The welding performance of stainless steel is better than that of aluminum.

  • Aluminum is the first choice for lightweight conductive material, which achieves a good balance between conductivity and cost.

  • Aluminum is more suitable for die casting or extrusion, while austenitic stainless steel also has good formability and does not require additional processing.

  • The cost of stainless steel and aluminum fluctuates greatly according to different models. Usually CNC machining stainless steel is more expensive than aluminum.