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The most common silvery metal options that instantly knock your head are either aluminum or stainless steel. Both are widely used but have differences in physical, chemical, and mechanical properties and also in their application.
So, let’s explore the difference between aluminum and stainless steel and find the best one for your project.
What is Aluminum?
Aluminum is one of the most abundant metals on the earth’s crust. It comprises about 8% of the earth’s weight! The greatest feature of this metal is it is very lightweight; aluminum weighs one-third the weight of steel. So, you can use it for applications where reducing weight is crucial.
Besides, aluminum is corrosion-resistant and has excellent heat and electricity conductivity. It is also malleable and non-toxic; you can use it in food packaging and utensils.
Common Aluminum Grades
| Aluminum Series | Main Alloying Element | Common Grades | Basic Features | Application |
|---|---|---|---|---|
| 1xxx Aluminium Grade Series | Pure aluminum (99%) | 1050, 1100 | – Soft and ductile – Good workability – Non-heat-treatable – Corrosion resistant | – Chemical equipment – Food processing and packaging – Railroad tank cars – Electrical transmission – Dials – Nameplates |
| 2xxx Aluminium Grade Series | Copper | 2024, 2124 | – High strength – Poor workability – Heat treatable | – Aircraft parts – Automobile applications |
| 3xxx Aluminium Grade Series | Manganese | 3003, 3105 | – 20% stronger than 1xxx series – Good workability – Corrosion resistant – Moderate strength | – Cooking utensils – Heat exchangers |
| 4xxx Aluminium Grade Series | Silicon | 4032, 4045 | – High wear resistance – Good weldability – Not heat-treatable | – Pressure cookers – Frying pans – Architectural designs |
| 5xxx Aluminium Grade Series | Magnesium | 5052, 5754 | – Moderate to high strength – High corrosion resistant – Not heat-treatable – Good weldability | – Constructions – Shipbuilding industry – Storage tanks – Pressure vessels – Electronics – Window frames – Beverage cans |
| 6xxx Aluminium Grade Series | Silicon and magnesium | 6061, 6063 | – Moderate to high strength – High corrosion resistant – Not heat-treatable – Good weldability | – Aircraft – Automotive – Architectural & – Marine applications |
| 7xxx Aluminium Grade Series | Zinc and magnesium | 7075, 7050 | – Good corrosion resistance – Heat-treatable – Highest strength – Mediocre weldability | – High-stress parts – Aircraft structures – Hydraulic equipment – Mobile |
What is Stainless Steel?
Stainless steel is known for its high anti-corrosion-resistant properties and greater strength. This is mainly made of iron with other alloying elements, primarily chromium. Other alloying elements include molybdenum, carbon, nickel, sulfur, etc. Based on this alloying element, stainless steel can be of different types and grades. The five types of stainless steel are:
- Austenitic
- Ferritic
- Martensitic
- Duplex
- Precipitation-Hardening (PH)
Compared to aluminum, stainless steel is more durable and can withstand high temperatures. These are widely used in heavy-duty applications in the industrial sector.
Common Stainless Steel Grades
| Type | Common Grades | Composition | Applications |
|---|---|---|---|
| Austenitic | 304 | Chromium (18–20%) Nickel (8–10.5%) | – Kitchen equipment – Sinks – Building facades – Food processing |
| 316 | Chromium (16–18%) Nickel (10–14%) Molybdenum (2–3%) | – Marine applications – Chemical processing – Surgical tools | |
| 310 | Chromium (24–26%) Nickel (19–22%) | – Furnace parts – Heat exchangers – Kilns | |
| Ferritic | 430 | Chromium (16–18%) | – Automotive trim – Appliances – Roofing materials |
| 409 | Chromium (11.5–13.5%) | – Automotive exhaust systems – Mufflers | |
| Martensitic | 410 | Chromium (11.5–13.5%) | – Cutlery – Surgical instruments – Fasteners |
| 420 | Chromium (12–14%) | – Knife blades – Surgical tools – Valves | |
| Duplex | 2205 | Chromium (22–24%) Nickel (4.5–6.5%) Molybdenum (3–3.5%) | – Oil and gas industries – Marine equipment |
| Precipitation-Hardening (PH) | 17-4 PH | Chromium (15–17.5%) Nickel (3–5%) Copper (3–5%) | – Aerospace components – Chemical processing – Nuclear industries |
Aluminum vs Stainless Steel: Know The Differences
1. Composition
Aluminum (AI) is a single element in its pure form. However, to boost its strength and physical properties, different elements like manganese, silicon, zinc, copper, etc. are alloyed with it. For example, the 6061 Aluminum contains magnesium (1%) and silicon (0.6%). Meanwhile, another popular grade, 7075 aluminum, contains zinc (5.6%) and copper (1.6%). The most common alloying elements used in aluminum are as follows:
| Common Alloys Of Aluminum | Typical Percentage in Alloys |
|---|---|
| Silicon (Si) | 4% to 13% |
| Magnesium (Mg) | 0.5% to 5% |
| Copper (Cu) | 2% to 10% |
| Zinc (Zn) | 3% to 8% |
| Manganese (Mn) | 0.3% to 1.5% |
| Iron (Fe) | 0.1% to 1% |
| Chromium (Cr) | 0.05% to 0.25% |
| Nickel (Ni) | 1% to 3% |
| Titanium (Ti) | 0.01% to 0.2% |
| Lithium (Li) | 1% to 2% |
In contrast, stainless steel is not a single element but an alloy of iron (Fe). It also contains a wide variety of alloying elements depending on the type and grade of the stainless steel. Yet the most common alloying elements used in different grades of stainless steel are as follows:
| Common Alloys Of Stainless Steel | Percentage By Weight |
|---|---|
| Chromium | 16% to 18% |
| Carbon | 0.030% |
| Manganese | 2% |
| Silicon | 0.75% |
| Nickel | 10% to 14% |
| Molybdenum | 2% to 3% |
| Phosphorus | 0.045% |
| Sulfur | 0.030% |
| Nitrogen | 0.10% |
| Iron | 7% |
2. Color
Stainless steel is of bright silver color and it’s very shiny and reflective. Depending on your application needs, you can get polished, brushed, satin, or matte finish options in stainless steel. As it has a chromium-rich oxide layer, this metal doesn’t tarnish or darken easily. So, for a natural metallic color, stainless steel is best.
Aluminum, on the other hand, is a silver-white matte finished metal. It is more of a light grey tone. You can polish it to get a mirror-like finish, but it doesn’t come out as shiny as stainless steel. Besides, they easily darken and tarnish. The plus point is that you can easily anodize aluminum to create vibrant, durable color finishes (e.g., gold, black, blue). These customized aluminium are widely used in decorative and industrial applications.
3. Hardness
The hardness of any metal is its resistance against deformation. This is measured through different hardness tests. Comparing their hardness, stainless steel is much harder than aluminum. Depending on the grades, the Brinell Hardness (BHN) of stainless steel ranges from 80 to 600 HB. In contrast, for aluminum, it ranges from 15–150 BHN (varies with alloy).
Therefore, we can see that stainless steel is significantly harder than aluminum. Besides, the precipitation-hardened grades of stainless steel are the hardest variant that aluminum can’t beat. Nevertheless, for moderate hardness and lightweight application requirements, aluminum is best.
4. Density & Weight
The density of the metal affects its weight. Due to varying atomic structure and composition, there is a major difference in the density of stainless steel and aluminum. The density of pure aluminum is 2.7 g/cm3, whereas for stainless steel it is 8.0 g/cm3.
Due to this difference in density, stainless steel is three times heavier than aluminum. So, if you take sheets of the same size, one made of stainless steel and the other of aluminum, the latter one will be lighter. This makes aluminum lightweight and suitable for aircraft applications.
5. Strength-to-Weight Ratio
Aluminum is lightweight and has reasonable strength, which gives it a high strength-to-weight ratio. This makes it ideal for lightweight structural applications. For example, Aluminum alloys like 7075 have exceptional strength and are used in aircraft and automotive components.
In contrast, stainless steel is significantly stronger, but it weighs heavily due to its high density. This reduces its overall strength-to-weight efficiency. So, you should use stainless steel for applications where strength is more prioritized overweight. For example, stainless steel is ideal for construction or industrial machinery.
6. Corrosion Resistance
Stainless steel has superior resistance against corrosion. The high chromium content in this metal forms a chromium oxide layer, offering exceptional resistance to rust and corrosion. Besides, the grade containing molybdenum can withstand chlorides, moisture, and acidic environments. For instance, 316 stainless steel is suitable for marine use and doesn’t rust in a salty sea environment.
Like stainless steel, aluminum doesn’t contain chromium, so it lacks the protective chromium oxide layer that stainless steel has. However, when aluminum comes in contact with air, it forms aluminum oxide, which provides corrosion resistance to an extent. However, it is vulnerable to chlorides (e.g., saltwater) and acidic/alkaline conditions.
7. Durability
Stainless steel is stronger and harder than aluminum. Moreover, they are also corrosion-resistant. This obviously makes stainless steel more durable than aluminum. Again, aluminum loses strength at high temperatures (above 200°C) and may become brittle in extreme cold. So, it won’t be durable in high temperatures.
The case is not the same with stainless steel; it can withstand extremely high temperatures. Some grades are also highly corrosive and resistant to withstand chlorine or seawater, e.g., 316 marine grade stainless steel. Therefore, it can last longer in harsh environmental conditions than aluminum.
8. Machinability
Due to the low hardness of aluminum, it is very machining-friendly. You can easily cut, drill, or shape them while manufacturing. As aluminum is soft in nature, it causes minimal tool wear. The biggest point here is that machining aluminum is pretty fast, and you can machine it at high speed.
On the other hand, stainless steel is much harder than aluminum, and so it is difficult to machine. This also causes high tool wear, especially for austenitic grades, as they are very hard. The tools used for machining stainless steel are heavy-duty and more expensive. Moreover, the machining speed of stainless steel is three to four times less than that of aluminum.
9. Malleability & Formability
Formability refers to the ability of a metal to be shaped without losing its structural integrity or cracking. As aluminum is soft and has high ductility, you can easily shape it into complex structures. It also supports stretching, bending, or rolling without cracking. Thus, aluminum has excellent formability and malleability even at room temperature.
Stainless steel, on the other hand, is hard and less ductile than aluminum. Besides, it requires more force to shape and is prone to cracking during extreme deformation. However, austenitic grades (e.g., 304, 316) exhibit good formability and malleability.
10. Magnetic Property
Aluminum is non-ferromagnetic; that is, it doesn’t have magnetic properties. This makes it suitable for MRI machines, electrical wiring in sensitive environments, non-magnetic tools, and applications requiring materials that are unaffected by magnetic fields.
Stainless steel can be both magnetic and non-magnetic based on its type or grade. The ferritic and martensitic stainless steel contains iron and is magnetic. These variants are used in appliances and industrial machinery. The 3xx series, or the austenitic stainless steel, is non-magnetic and is used in medical devices, chemical processing, and environments where magnetism could interfere.
11. Yield Strength
The yield strength of stainless steel is much higher than that of aluminum. Based on the grades of the stainless steel, the yield strength usually ranges from 215–900 MPa. Martensitic grades usually have higher yield strength than austenitic-grade stainless steels.
On the contrary, pure aluminum has a low-yielding strength of just 30 MPa. However, depending on the alloying element, this can go high up to 500 MPa, which is less compared to stainless steel. This makes aluminum not a suitable metal for structural or engineering applications.
12. Tensile Strength
Stainless steel has about 34.4 times higher tensile strength than pure aluminum. It has a tensile strength of 34.5 to 3100 MPa. Such strength makes stainless steel highly suitable for heavy-load-bearing applications.
Meanwhile, pure aluminum has a tensile strength of only 90 MPa. So, they can easily get deformed under high pressure or excess loading. However, high-strength aluminum alloys can have a tensile strength of up to 690 MPa.
13. Shear Strength
Aluminum has lower shear strength than stainless steel. Pure aluminum has a shear strength of ~54 MPa (using 60% of UTS) only. So, at lower shear forces, pure aluminum goes through high deformation. However, the high-strength aluminum alloy has high shearing strength; for instance, aluminum 7075-T6 has a shear strength of 331 MPa.
In contrast, stainless steel has high shear strength ranging from 74.5 to 597 MPa. This resists cracking or tearing under heavy loads. So, for high-stress applications, stainless steel is better suited to use than aluminum.
14. Applications
| Industry | Application of Aluminum | Application Of Stainless Steel |
|---|---|---|
| Aerospace & Automotive | – Aircraft bodies – Car chassis – Fuel tanks – Marine parts | Engine components Exhaust systems Structural parts |
| Consumer Products | Laptops Smartphones Cans Cookware Utensils | Appliances Cutlery Cookware Jewelry |
| Construction | Window frames Roofing Curtain walls Scaffolding | Bridges Facades Handrails Structural supports |
| Industrial Use | Heat exchangers Lightweight piping Frames | Chemical tanks Factory equipment Cutting tools |
| Electrical Applications | Power lines Transformer windings Wiring | Electric enclosures Grounding equipment |
| Medical & Food | Food packaging | Surgical tools Implants Food processing tanks |
| Luxury & Aesthetics | Anodized panels Decorative items Lightweight designs | Polished jewelry Watches Home Decor |
15. Electrical Conductivity
Aluminum has an electrical conductivity of approximately 37.7 million S/m, equivalent to 61% IACS (International Annealed Copper Standard). This makes it a popular choice for electrical wiring and power transmission lines. So, aluminum is suitable for overhead power lines, transformer windings, and busbars in electrical substations.
Stainless steel has much lower electrical conductivity, approximately 1.45 million S/m, which is less than 3% IACS. Therefore, it is not typically used for electrical applications where conductivity is critical. However, its high corrosion-resistant properties make stainless steel suitable for applications requiring durability and low conductivity, such as heating elements or shielding materials.
16. Melting Point & Heat /Thermal Conductivity
Aluminium has a low melting point of 660°C and high thermal conductivity of 237 W m−1 K−1. It quickly absorbs and distributes heat, which is ideal for thermal management applications. This makes aluminum suitable for cookware or similar cases where heat transfer control is crucial. For example,- aluminum is used in heat exchanges, baking trays, automotive radiators, etc.
In contrast, stainless steel has a high melting point of 1400°C to 1530°C. Therefore, it has low thermal conductivity (15-25 W m−1 K−1); that is, it doesn’t easily disperse heat. So, stainless steel is not suitable for applications that require rapid heat transfer. But where you need to maintain a constant temperature, stainless steel is good to go.
17. Environmental Impact
Aluminum production involves bauxite mining, refining, and smelting, which requires high energy and disrupts the environment. Besides, smelting aluminum through the Hall-Héroult process consumes significant amounts of electricity. In contrast, stainless steel production involves mining iron ore, nickel, and chromium. The overall carbon footprint in producing stainless steel is lower compared to aluminum smelting.
Besides, stainless steel is more long-lasting and durable than aluminum. So, it needs less replacement than aluminum. Plus, it is 100% recyclable without quality loss and often contains over 60% recycled content. Thus, it ensures fewer products enter landfills, reducing waste generation.
18. Effect on Foods
Aluminum reacts with acidic or alkaline food, which can affect the taste and quality of the food. So, non-reactive coatings (e.g., anodization) are required for safe use in cookware.
In contrast, stainless steel is non-reactive and doesn’t react with any kind of food. Moreover, due to high-temperature resistance, you can use stainless steel as cookware. It is corrosion-resistant, too. So, all these features make stainless steel suitable for food-grade applications.
19. Cost
Aluminum is very affordable and widely available. But it is not as robust and durable as stainless steel. Aluminum can’t withstand high temperatures or impact as stainless steel can.
Though stainless steel is more expensive than aluminum, it is worth the price for its durability. It is used in heavy-duty applications and can withstand harsh weather conditions. So, for industrial needs, investing in stainless steel is worthwhile.
Overall Comparison Chart: Aluminum vs Stainless Steel
| Criteria | Aluminum | Stainless Steel |
|---|---|---|
| Color | Silver-white | Bright Silver |
| Hardness | 15–150 BHN | 80 to 600 HB |
| Density | 2.7 g/cm3 | 8.0 g/cm3 |
| Strength-to-Weight Ratio | High | Low |
| Magnetic | No | Yes (except austenitic grade) |
| Durability | Moderate | High |
| Corrosion Resistance | Moderate | High |
| Machinability | High | Low |
| Mealability | High | Low |
| Formability | High | Low |
| Yield Strength | 30–500 MPa | 215–900 MPa |
| Tensile Strength | 90 to 690 MPa (based on alloy) | 34.5 to 3100 MPa |
| Shear Strength | 54 to 331 MPa(based on alloy) | 74.5 to 597 MPa |
| Electric Conductivity | 37.7 million S/m | 1.45 million S/m |
| Melting Point | 660°C | 1400°C to 1530°C |
| Thermal Conductivity | 237 W m−1 K−1 | 15 to 25 W m−1 K−1 |
| Cost | Cheap | Expensive |
Which Metal Is Best For Your Needs: Aluminum Or Stainless Steel?
The best metal depends on your application needs. For harsh weather that deals with chlorine or other toxic chemicals, stainless steel is better as it is non-reactive. This also supports heavy-duty, industrial-grade applications. Again, stainless steel is best for use where the metal needs to go through extreme heat and high load.
However, if you need lightweight metal, aluminum is the better option. You can use it for aerospace and other weight-sensitive applications. Besides, its high malleability and machinability facilitate complex shaping. So, aluminum works great when making complex lightweight parts that can deal with a moderate load. It is also affordable and a good-to-go metal if you are on a tight budget.
Wrapping Up
Before choosing between aluminum and stainless steel, consider your application requirements. For heavy-duty applications requiring greater strength and greater corrosion resistance, choose stainless steel. And for lightweight applications with moderate strength needs, aluminum is good to go.
Whether you are working with aluminum or stainless steel, RICHCONN offers you a CNC machining facility for both metals. You can choose the grade of the metal and place your order for machining aluminum or stainless steel. Go through our service page for details, and get a free quote.
FAQs
What is cheaper, stainless steel or aluminum?
Aluminum is more widely available and cheaper than stainless steel. However, the price varies for different grades or alloying elements.
Is aluminum or stainless steel more heat resistant?
Stainless steel is more heat resistant than aluminum. It has a higher melting point of 1400°C to 1530°C, which is much greater than that of aluminum. Thus, stainless steel can withstand high temperatures where aluminum melts above 660°C (approx).
Does stainless steel heat up faster than aluminum?
No, stainless steel has lower thermal conductivity than aluminum. Therefore, it takes more time to heat up compared to aluminum.
Which aluminum or stainless steel is better for your health?
Aluminum is reactive to acid and alkaline. So, if you put food in an aluminum container, it can contaminate the food and affect your health. In contrast, stainless steel is non-reactive to alkaline and acidic food and causes no harm to health.
Does aluminum corrode faster than stainless steel?
Yes, aluminum corrodes faster than stainless steel. It at once forms a thin, protective aluminum oxide layer when it comes in contact with air. This prevents corrosion in mild conditions, but the oxide layer breaks down in marine, salty, or acidic environments. This leads to corrosion. In contrast, stainless steels have chromium, nickel, and molybdenum that offer high resistance against corrosion. Some grades also withstand marine and chlorine.
