Aluminum Vs Stainless Steel: 8 Differences!

Aluminum and stainless steel are popular materials. Manufacturers use CNC machining to cut and shape these materials, creating the desired parts. However, these two materials differ from each other in various aspects. Those differences lead people to debate the aluminum vs stainless steel topic.

 

We offer CNC machining services, and our clients always ask whether they should use aluminum or stainless steel. We always answer, ‘It depends on your needs.’ It is key to understand the differences between these two materials to make wise decisions. In this article, I’ll explain all the key differences between aluminum and stainless steel. 

 

What are the Differences Between Aluminum & Stainless Steel?

 

These two materials offer pros and cons. We utilize CNC machining to cut and shape these materials, producing a range of parts. Both have different properties, which significantly change their usability. For example, aluminum is lightweight and soft. Stainless steel is durable, robust, and comes with exceptional rust resistance. 

 

We first analyze the purpose of each part and then use the most suitable material. Let’s dive in and discuss the differences between these two materials:

 

1- Composition

Aluminum and stainless steel differ in their chemical composition. Aluminum is a naturally occurring element found in the Earth’s crust. Generally, it is available and used in the pure form. Remember, aluminum is soft and lightweight in its pure form. However, some manufacturers add other elements to aluminum to create aluminum alloys. 

This is done to get the desired properties from the aluminum. On the other hand, stainless steel is an alloy composed of multiple elements. Those include iron, chromium, nickel, molybdenum, and manganese. Each of these alloy elements gives specific properties to stainless steel. For example, chromium enhances its resistance to rust, and nickel provides it with additional strength. 

Here is a table showing the chemical composition of stainless steel:

 

Element	Typical Range (%)
Iron (Fe)	Balance (principal component)
Chromium (Cr)	10.5% – 20%
Nickel (Ni)	0% – 14%
Carbon (C)	0.03% – 1.2%
Manganese (Mn)	0.1% – 2%
Molybdenum (Mo)	0% – 3%
Silicon (Si)	0.2% – 1%
Phosphorus (P)	< 0.05%
Sulfur (S)	< 0.03%

 

Remember, stainless steel is available in various grades, including 316, 304, and 410. The chemical composition of each of these grades differs from that of the others. For example, 410 grade has only 11.5 – 13.5% chromium. On the other hand, grade 304 has a higher chromium content of 18-20%. Similarly, the proportion of different elements can also vary. 

 

2- Weight & Strength 

Aluminum is known for its lightweight. It has a density of 2.7 g/cm³.  You’ll see many parts of aircraft made of this material. The reason is that aluminum is lightweight, which reduces the overall weight of the plane. As a result, aircraft fuel consumption decreases. 

On the other hand, stainless steel is a heavy-duty material. Its weight (7.8 g/cm³) is almost three times that of aluminum. Its higher weight is advantageous as it makes stainless steel robust and rugged. Therefore, it is very durable and stronger, able to bear extreme stress and load. Remember, aluminum is lightweight, but its strength is less than that of stainless steel. 

 

3- Rust Resistance

Both aluminum and stainless steel are resistant to rust. However, stainless steel performs well and doesn’t get rusty even in moist conditions. Remember, when aluminum comes in contact with oxygen, it makes aluminum oxide. 

This oxide layer protects the aluminum from rusting. However, this layer is not very durable, which is a drawback. The stainless steel has over 10.5% chromium. Chromium reacts with oxygen to form a chromium oxide layer. This layer is highly durable, protecting the stainless steel from rust and corrosion. 

Even in extreme conditions, this chromium layer does not get rusty. Therefore, you’ll see many parts made with stainless steel used in marine applications. The aluminum oxide layer generally deteriorates over time. Moreover, consistent exposure to moisture or salty water also damages this layer. Aluminum is less effective in terms of rust resistance. 

 

4- Machinability & Weldability

Aluminum is a superior option in terms of weldability and machinability. The reason is that aluminum is relatively softer and can be cut and shaped easily. Moreover, it has better thermal conductivity. So it dissipates the heat quickly when CNC machines cut it. 

As a result, the cutting tools do not wear out. Due to effective heat dissipation, the cutters also remain cool and do not overheat. On the other hand, stainless steel is a robust and durable material. So, it is very challenging to cut and shape this material. The cutters must apply more power, which can result in overheating.

The CNC machining of aluminum is easier and machine-friendly. Aluminum also wins the race when it comes to weldability. This is due to the better thermal conductivity of this material. Remember, welding stainless steel material can also be done. However, this material has lower heat dissipation, which can result in distortion at the weld spot. 

 

5- Thermal Conductivity & Heat Resistance

As I said earlier, aluminum has excellent thermal conductivity. It means that it can transfer heat from one point to another very quickly. So, it is used in heat sinks, engine components, and cooling systems. If you heat an aluminum part, the heat will soon spread from one end to the other. 

This property makes aluminum suitable for use in the electronics industry. It won’t overheat due to a balanced distribution of heat. On the other hand, stainless steel has compromised thermal conductivity. So, it does not transfer the heat effectively. Therefore, this material is used where heat insulation is required. 

It won’t allow heat to transfer easily. The melting point of aluminum is lower, i-e, 660°C. It quickly melts and cannot resist heat. On the other hand, stainless steel is a very thermally stable material. Its higher melting point of 1000°C makes it an excellent heat-resistant material. This material is used to manufacture exhaust systems, ovens, and other related products. 

 

6- Aesthetics Appeal & Durability

Both aluminum and stainless steel have excellent physical appearance. Aluminum looks matte silver and has a smooth surface. Manufacturers further add coatings to enhance the rust resistance of aluminum material. This coating enhances the look and feel of this material. However, aluminum can get scratches if used harshly.

On the flip side, stainless steel has a bright, shiny surface. It looks more polished and aesthetically appealing. Interestingly, the stainless steel material keeps its shine and charm for a longer duration. It does not deteriorate and remains scratch-resistant, even in the harshest conditions. 

Stainless steel surpasses aluminum in terms of durability. The reason is that it has better strength and hardness due to the presence of nickel. Additionally, the presence of chromium makes this material corrosion resistant. Aluminum is soft and less rigid, which makes it less durable. It also gets rusty when used in harsh conditions. 

 

7- Magnetic Nature

Aluminum is a non-magnetic material in all of its forms. It won’t show any love or attraction towards the magnet. Remember, non-magnetic materials are not ideal for CNC machining. The reason is that the chips produced during machining don’t collect at a single point. So their chip evacuations or management can be challenging.

You’ll need to manually remove chips during the machining of non-magnetic materials. Stainless steel is also non-magnetic; however, some grades exhibit magnetism. Here is a table showing the magnetic behavior of different grades of stainless steel:

 

Stainless Steel Grade	Type	Magnetic Behavior
304	Austenitic	No (mostly non-magnetic)
316	Austenitic	No (mostly non-magnetic)
430	Ferritic	Yes
410	Martensitic	Yes

 

8- Cost & Applications

Aluminum is less costly and readily available. As I said earlier, this material is obtained from the Earth’s crust. It is present in abundance in the Earth’s crust. Moreover, its machining cost is also very low, which is a big plus. It has better heat conductivity (dissipation) and is soft. 

The cutting tools easily cut it without overheating. This ensures less wear and tear on the cutters. On the other hand, stainless steel is strong and rigid. It is considered a premium and very expensive material. Moreover, the costs of stainless steel CNC machining can exceed your budget. It has lower heat conductivity, which can cause the cutting tools to overheat, resulting in increased wear and tear. 

Here is a table showing a comparison of the application of these two materials:

 

Aluminum Applications	Stainless Steel Applications
Aircraft frames, body panels, fittings	Engine components, structural supports
Engine blocks, wheels, heat exchangers	Exhaust systems, trim, and fasteners.
Laptop bodies, smartphone frames	Enclosures, connectors, and brackets.
Prosthetic parts, light equipment frames	Surgical tools, hospital equipment, trays
Window frames, roofing, and curtain walls	Railings, cladding, and structural components
Boat hulls, masts, deck parts	Propellers, pumps, underwater hardware
Bicycles, flashlights, furniture frames	Appliances, cutlery, water bottles

 

Which One Should You Choose, Aluminum or Stainless Steel?

 

As mentioned earlier, both aluminum and stainless steel have their unique value propositions. Aluminum is lightweight, but stainless steel is stronger and more durable. Their selection can vary according to individual needs and preferences.

 

I recommend using stainless steel due to its better properties. It is rust-resistant, robust, and heat-resistant. Moreover, its physical appearance is also attractive, making it ideal for decorative products. However, aluminum is a cost-effective material, suitable for budget-friendly projects.

 

Remember, stainless steel is a premium material, and its higher cost can be a genuine hurdle for many. Therefore, I present aluminum as a more affordable alternative to stainless steel. Its properties don’t match stainless steel, but it can be a good starting point for someone with a tight budget.

 

Frequently Asked Questions

 

Is stainless steel better than aluminum?

Yes, stainless steel is better due to its excellent strength and corrosion resistance. Moreover, its heat resistance also makes it a superior option over aluminum. However, aluminum is a cheaper alternative to stainless steel with some compromised properties. 

 

Which lasts longer, stainless steel or aluminum?

Stainless steel is more durable, strong, and rigid. Moreover, it contains chromium, which makes it resistant to rust. So, stainless steel material lasts longer than aluminum. 

 

What is healthier to cook with, aluminum or stainless steel?

I consider stainless steel a healthier option for utensils and cooking products. The reason is that this material is non-reactive. It remains safe even at very high temperatures.

 

Is stainless steel exhaust better than aluminum?

Yes, stainless steel has a higher melting point of 1,000 degrees Celsius. This material can withstand high temperatures (heat) easily. Therefore, using stainless steel to make the exhaust is a wise option.

 

Can stainless steel rust?

Generally, stainless steel is rust-resistant due to the presence of chromium. This chromium forms an oxide layer, known as chromium oxide. It protects the surface of stainless steel from corrosion even in harsh or salty conditions. 

 

Conclusion

 

Both of these materials have pros and cons. So, I recommend you carefully analyze your needs before choosing between aluminum and stainless steel. If you prefer a lightweight product, opt for aluminum. However, if strength, durability, and overall longevity are necessary, stainless steel is the best choice. In this article, I explained eight significant differences between these two materials. You should read it carefully and then make a final decision between aluminum and stainless steel.