Aluminum vs stainless steel

What is aluminum

Aluminum is a lightweight metal material with strong corrosion resistance. The strength of aluminum itself is not high, but the strength of aluminum alloy is improved after adding some elements.

Physical properties of aluminum

The density of aluminum and aluminum alloys is 2.7g/cm³, the melting point is 660°C, the boiling point is 2520°C, and they have strong electrical conductivity, thermal conductivity, ductility and corrosion resistance. Therefore, aluminum and aluminum alloys are widely used in the fields of automobile industry, aerospace industry, shipbuilding, construction applications, pharmaceutical and food packaging, etc.

Aluminum vs stainless steel

What is stainless steel

Stainless steel is a type of alloy made primarily from iron and carbon, with a significant addition of chromium, usually at least 10.5%. This chromium content is what gives stainless steel its remarkable corrosion resistance, as it forms a thin, passive layer of chromium oxide on the surface that prevents rust and degradation when exposed to moisture and air.

Physical properties of stainless steel

Stainless steel exhibits a range of physical properties that make it a versatile material for many applications. Here are the key physical properties of stainless steel:

1. Density

• – Typical Range: 7.75 to 8.1 g/cm³.
• – Description: The density of stainless steel is relatively high, contributing to its strength and durability. The exact density can vary slightly depending on the specific alloy composition.

2. Melting Point

• – Typical Range: 1,370°C to 1,530°C (2,500°F to 2,800°F).
• – Description: Stainless steel has a high melting point, which makes it suitable for applications involving high temperatures, such as in furnaces and jet engines.

3. Thermal Conductivity

• – Typical Value: 16 to 24 W/m·K (watts per meter-kelvin) at room temperature.
• – Description: Stainless steel has lower thermal conductivity compared to other metals like copper or aluminum, which means it is less efficient in transferring heat. This property is advantageous in applications requiring heat retention.

4. Thermal Expansion

• – Coefficient of Thermal Expansion: Approximately 16.5 to 18.5 x 10⁻⁶ /°C.
• – Description: Stainless steel expands and contracts with temperature changes. The coefficient of thermal expansion is important in applications where dimensional stability is critical, such as in construction and manufacturing.

5. Electrical Conductivity

• – Typical Value: 1.45 to 1.6 x 10⁶ S/m (siemens per meter).
• – Description: Stainless steel has relatively low electrical conductivity compared to other metals like copper. This makes it less suitable for electrical applications but is beneficial for use as a resistive material.

6. Magnetic Properties

• – Description: The magnetic properties of stainless steel vary depending on the alloy. Austenitic stainless steels (e.g., 304, 316) are generally non-magnetic, while ferritic and martensitic stainless steels can be magnetic.

7. Tensile Strength

• – Typical Range: 515 to 827 MPa (megapascals).
• – Description: Stainless steel is known for its high tensile strength, which refers to the maximum stress it can withstand while being stretched or pulled before breaking. This makes it ideal for structural and load-bearing applications.

8. Hardness

• – Typical Value: Varies with the alloy, but generally between 140 to 300 on the Brinell scale.
• – Description: Stainless steel exhibits good hardness, meaning it resists deformation and scratching. Hardness can be increased through processes like work hardening.

9. Ductility

• – Description: Stainless steel is generally quite ductile, meaning it can be drawn into wires or other shapes without breaking. This property is essential in forming and shaping the material into various products.

10. Corrosion Resistance

• – Description: One of the most notable properties of stainless steel is its excellent resistance to corrosion. The chromium in the alloy forms a passive oxide layer on the surface, protecting it from rust and other forms of corrosion, even in harsh environments.

Stainless steel and its applications

11. Modulus of Elasticity

• – Typical Value: 193 to 200 GPa (gigapascals).
• – Description: This property measures the stiffness of stainless steel, indicating how much it will deform under a given load. A high modulus of elasticity means the material is stiff and resists deformation.

Aluminum vs stainless steel

Corrosion resistance

Both aluminum and stainless steel have strong corrosion resistance. Although they have different compositions, the principle of rust prevention is to generate a dense oxide layer to prevent the product from corrosion.

Aluminum naturally forms a thin layer of aluminum oxide when exposed to air, which provides decent corrosion resistance. This oxide layer is relatively stable and protects the underlying metal from further oxidation.

Stainless steel’s corrosion resistance comes from its chromium content (usually at least 10.5%). Chromium reacts with oxygen to form a very stable and protective chromium oxide layer on the surface, which prevents further corrosion.

Strength

In the selection of materials, strength is a property that cannot be ignored. Generally, the strength of aluminum alloy is not as good as that of stainless steel, but some aluminum alloys with relatively high strength, such as 2024, 7075, have strength.

The strength of stainless steel is generally higher than that of aluminum alloy. This conclusion is based on the comparison of the physical and mechanical properties of the two materials. Stainless steel, as an alloy steel, is mainly composed of elements such as iron, chromium, and nickel, and has good corrosion resistance, high temperature resistance, wear resistance, and excellent mechanical properties. The strength of stainless steel can be further enhanced by cold hardening or heat treatment, so that it has higher strength and hardness, as well as better fatigue resistance and impact resistance.

In contrast, although aluminum alloy has the characteristics of low density, high strength, good plasticity, excellent electrical and thermal conductivity, and its strength can be enhanced by alloying heat treatment, its strength is usually difficult to reach the level of stainless steel. The strength of aluminum alloy is comparable to that of high-quality steel and can meet the requirements of many structural parts, but its wear resistance and high temperature resistance are relatively poor in the untreated state.

Aluminum alloy and its application

Therefore, in applications requiring high strength, stainless steel is usually a better choice. Aluminum alloys are widely used in aviation, automobile, electronics and other fields due to their light weight and good processing properties.

Strength-to-weight ratio

Aluminum alloys have a higher strength-to-weight ratio than stainless steel.

Although stainless steel is stronger than aluminum alloys, aluminum alloys have a lower density than stainless steel. The density of aluminum alloys is 2.7g/cm³, while the density of stainless steel is 7.75 to 8.1 g/cm³. The density of aluminum alloys is about 1/3 of that of stainless steel.

Aluminum alloys are lightweight metals with a high strength-to-weight ratio. Its tensile strength is usually around 60,000 PSI, while some alloys can even reach 100,000 PSI. The advantages of aluminum alloys are good plasticity and easy processing into various shapes and sizes. In contrast, although stainless steel has the benefit of resisting corrosion and oxidation, its tensile strength is between 30,000-50,000 PSI, but it is denser than aluminum alloys and may be more difficult to process.

In summary, aluminum alloys have lighter weight and better processability while maintaining high strength, making them a superior choice in many applications.

Price

Generally speaking, the price of stainless steel is higher than that of aluminum alloy. When both materials can meet the performance requirements of the product, aluminum alloy is undoubtedly the best choice to reduce costs.

The price of stainless steel is higher than that of aluminum alloy, and the density is also higher than that of aluminum alloy. The same one ton of aluminum alloy can produce three times the same volume of stainless steel products. Therefore, when both can meet the performance requirements, aluminum alloy is the most affordable choice.

What is the difference between aluminum alloy and stainless steel?

• 1. Material composition: Stainless steel contains elements such as iron, chromium, and nickel, while aluminum alloy mainly contains aluminum and a small amount of magnesium, silicon, and other elements.
• 2. Performance characteristics: Stainless steel has good corrosion resistance, wear resistance, and high-temperature strength, while aluminum alloy has high electrical conductivity, thermal conductivity, and low density.
• 3. Appearance color: The surface of stainless steel is silvery white, while the surface of aluminum alloy is silvery white or light yellow.
• 4. Price: The price of stainless steel is usually higher than that of aluminum alloy.
• 5. Application: Stainless steel is commonly used in construction, furniture, kitchenware, and other fields, while aluminum alloy is commonly used in aviation, automobiles, construction, and other fields.

How to choose aluminum alloy and stainless steel

Both aluminum alloy and stainless steel have high strength, high corrosion resistance, electrical conductivity, thermal conductivity and other properties, but there are still some gaps in specific single properties. In terms of material selection, we must consider the application scenario of the material.

If the application scenario of the product has high requirements for strength and no requirements for weight, then stainless steel is the best choice.

If the application scenario of the product has requirements for lightweight and requires a high strength-to-weight ratio, then aluminum alloy is better than stainless steel.