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The use of stainless steel and aluminum today has become inevitable. It has nearly become impossible to go about one’s day without coming in contact with aluminum or stainless steel. These two metals are found in cars, kitchens, bridge constructions, aircraft, building constructions, and many more.
Although stainless steel and aluminum may look similar in appearance, they exhibit different properties that differentiate both metals for use in the manufacturing industry.
Consequently, making the best decision about your project design isn’t enough, rather the metal type also plays a major role in the success and longevity of the project.
Due to this, this article seeks to draw a comparison between stainless steel and aluminum using about 17 properties.
Stainless steel and aluminum exhibit a vast variety of impressive properties that can be used to differentiate both metals. These properties will be used in this chapter to differentiate stainless steel from aluminum. These characteristics include element composition, corrosion resistance, electrical resistance, thermal conductivity, melting point, hardness, weight, and more.
The consideration of the elemental composition of the metal is crucial in the selection of material for a project. This is because, the components of such metal are responsible for its properties such as hardness, corrosion resistance, melting point, and many more. When compared, stainless steel is composed of a vast variety of elements in different proportions. Stainless steel contains chromium (11%) while other elements range in composition from about 0.03% to over 1.0%. Other components include aluminum, silicon, sulfur, nickel, selenium, molybdenum, nitrogen, titanium, copper, and niobium.
As said, each elemental composition plays an active role in the properties of the metal, for example, the chromium content is responsible to provide heat and corrosion resistance.
On the other hand, aluminum contains different constituents including aluminum, silicon, zinc, magnesium, manganese, copper, iron, titanium, chromium, zirconium, and many more.
Both stainless steel and aluminum exhibit excellent corrosion resistant properties. However, stainless steel has an edge over aluminum due to its elemental composition. Stainless steel is made up of chromium, iron, nickel, and more. The chromium is an added agent to help give stainless steel an invisible shield to prevent corrosion. When rusting of stainless steel occurs, this protective layer takes the brunt of it. Whenever the rust on its surface is scrubbed off, the chromium shield content of stainless steel simply renews itself.
On the other hand, aluminum does not rust the same way stainless steel does, but rather aluminum corrode. Interestingly, aluminum has a shield which is a thin protective layer of aluminum oxide that prevents its surface from rust. However, the protective shield – aluminum oxide does not prevent aluminum from other forms of corrosion.
Electrical conductivity is a fundamental property of a metal that quantifies how strongly it conducts electric current. To determine the electrical conductivity of stainless steel and aluminum, copper is used as a standard to rate both metal’s conductivity. This is because copper is highly conductive and it is ranked 100 on a scale of 0 to 100.
In comparison relative to the electric conductance of copper, aluminum is a better conductor than steel. It exhibits about 61 percent of copper’s conductivity with about 30% of copper’s weight. This makes it an ideal material for use in long-distance electrical transmission and high voltage overhead power lines. In contrast with aluminum relative to the electric conductance of copper, stainless steel is a poor conductor. It only exhibits about 3.5% of copper’s conductivity.
Thermal conductivity is a crucial factor to consider when selecting a material for your project. The thermal conductivity of a metal is referred to as its ability to conduct or transfer heat. In some applications, it’s important to determine the thermal conductivity to know which material is the perfect choice. In essence, a good radiator must have a high rate of conductivity while a material with low thermal conductivity is a good insulator.
In comparison, aluminum has a much better thermal conductivity of 1460 BTU-in/hr-ft²-°F (210 W/m-K). This is why it is mostly used for air conditioning units and radiators. On the other hand, stainless steel can be used at much higher temperatures compared to aluminum which mostly becomes soft at a temperature above 400-degree Fahrenheit.
The melting point of a material is also important in material selection. This is because metals are most formable when they are in a liquid state. This means that the melting point can be used to determine the formability of a material. Another thing to consider is that component failure can occur once a material reaches its melting point or temperature.
Therefore, the melting point is the temperature at which a material begins to transform from a solid-state to a liquid state. In comparison, stainless steel has a higher melting point ranging from 1230 °C to about – 1530 °C (2250 – 2790 °F). On the other hand, aluminum exhibit a lower melting point of 660.37 °C (1220.7 °F) compared to stainless steel. This shows that stainless steel is more applicable for a heat resistance application than aluminum.
When it comes to hardness, it is the comparative value of the metal that describes the metal’s response to etching, deformation, denting or scratch along its surface. This hardness test is widely carried out in the manufacturing space with a tool known as an indenter machine.
The hardness of a material is important in obtaining the strength of the material. It is measured using several methods, in this case, we are using the Brinell’s scale as a mean of measuring the hardness of stainless steel and aluminum hardness for comparisons. The Brinell’s hardness of stainless steel (80 – 600 HB) is greater than that of aluminum (15 HB), hence, stainless steel is harder to form compared to aluminum. Therefore, in applications that require hardness, stainless steel is preferred over aluminum.
Generally, aluminum is typically not as strong as stainless steel which can be recycled without losing strength. It is about one-third of the weight of stainless steel. Aluminum exhibit a density of 2.7 g/cm3 while stainless steel exhibit about 8.0 g/cm3. These values show that aluminum is lighter in weight than stainless steel. As a result of the lightweight aluminum, it is mostly used in skyscrapers and airplanes. Recently, the majority of the world’s skyscrapers are built out of aluminum.
Also, aluminum alloys are developed to be stronger compared to pure aluminum so that they can support the weight of heavy glass panes used for constructing tall buildings.
A material is said to be durable if it remains functional without the use of excessive repairs or maintenance whenever it is acted upon by challenges of normal operations. Aluminum and stainless steel are both durable in their respective domain. However, it is crucial to determine the most durable material especially when durability is a crucial entity in your project requirement.
In comparison, in terms of strength and hardness, stainless steel is considered the undisputed winner. This is why the vast majority of trucks and cars feature more stainless steel than aluminum. Stainless steel is stronger, and more durable than aluminum, hence it is preferred over aluminum in automotive and similar applications.
The machinability of any material is referred to the ease with which the material can be machined. Also, how machinable the material is dependent on the cutting condition and physical properties of the material.
In this case, aluminum is more machinable than stainless steel and most metals. This is attributed to the fact that its lower hardness that makes it chip easily when machined. It can be said that aluminum is relatively easy to shape than stainless steel. Easy chipping means the metal is more free machining with the depiction that the cutting tools spend more time and effort cutting the work-piece rather than the chips it has just created. Aluminum can also be machined up to 3 times or 4 times faster than stainless steel.
Formability is the ability of a material to exhibit plastic deformation when formed without getting damaged. Stainless steel is resistant to wear and abrasion and it’s harder compared to aluminum which is fairly soft and easier to form and cut. Most aluminum tempers and alloys dent, ding, or scratch more easily as compared to stainless steel. While stainless steel is strong and hard, it is less likely to warp, deform or bend under the application of weight, force, or heat. In an application where the formability of material is deemed important for a project, aluminum is a perfect choice.
Choosing stainless steel or aluminum for a project often comes down to application. Whether welding aluminum parts or stainless steel parts, a quality weld is always required. Aside from having different varieties of quality that can be quite advantageous for different industrial applications, stainless steel, and aluminum weld differently too.
When we compare, welding of stainless steel is fairly cost-effective and easy to carry out than aluminum welding. The welding of aluminum requires more skills and cleanliness but aluminum parts are resistant to corrosion and lighter in weight. On the other hand, stainless steel is 2.5 times heavier and much stronger than aluminum. Consequently, it can bend and distort when welded but does no easily crack compared to aluminum.
The yield tensile strength of a partis the highest stress with which part or material begins to deform permanently while the yield point is the point where non-linear deformation begins. Once a material has passed its yield point, some fraction of the deformation will be permanent and non-reversible. Aluminum exhibit a yield strength ranging from 7 MPa for low-strength aluminum up to about 11 MPa for high strength aluminum.
On the other hand, stainless steel exhibit yield strength ranging from 25 MPa for a low strength stainless steel to about 2500 MPa for a high strength stainless steel. Therefore, if your project requirement has to do with yield strength, then stainless steel is preferred.
The ultimate tensile strength is referred to as the highest on the curve of stress-strain. This is said to be the maximum stress that a material can sustain in tension. If this stress is applied and maintained, it will result in a fracture. In most cases, this value is significantly higher than the yield stress of about 50 to 60 % more than the yield for few metals.
In this case, we compared stainless steel with aluminum, which shows that stainless steel exhibited higher tensile strength than aluminum. Stainless steel exhibited 34.5 – 3100 MPa while pure aluminum exhibits a tensile strength of 90 MPa and can be increased to over 690 MPa for some heat-treatable alloys of aluminum.
The shear strength of a material is its resistant properties against shear load before the component fails in shear. This phenomenon majorly occurs normally on a plane in a parallel direction to the direction of the force acting on it. Stainless steel shear stress is rated between 74.5 – 597 MPa depending on alloy properties while the shear strength of aluminum is rated between 85 to about 435 MPa. This depicts that in applications that require high resistance against shear load, stainless steel is a perfect choice over aluminum.
To avoid using the wrong material for your project, it advisable that users must be conversant with the color of materials to be used. In this case, aluminum and stainless steel are two metals that look very similar but are different.
Aluminum exhibit a silvery-white appearance that varies in color from silver to dull grey depending on the material’s surface. The appearance of aluminum is normally towards silver for smooth surfaces. Stainless steel in contrast with aluminum is relatively shiny and exhibits a tint that is more silver than grey. In most cases, stainless steel will still be shinier and brighter compared to the appearance of aluminum even when these appearances have been tampered with over time by the weather.
Stainless steel in the industrial space is now being used in vast varieties of applications. While it is 100% recyclable, it is found almost in everywhere and citizen interacts with products manufactured with stainless steel daily. This application ranges from the kitchen, road, hospitals, buildings, and many more. Below are the major applications of stainless steel:
Generally, aluminum is usually used in vast varieties of industries due to its excellent corrosion resistance. It exists in a vast variety of alloys and forms which markedly help to improve aluminum mechanical characteristics especially when tempered. The most common form of aluminum alloy for example is its form as foils and beverage can which are made up of 92% to about 99% aluminum. The following are the major application of aluminum:
In weight comparison, aluminum is relatively more expensive than stainless steel. However, aluminum is about one-third of stainless-steel’s weight. As a result, when the same volume of stainless steel and aluminum are placed side by side, stainless steel is more expensive usually by 30%. This means that if the cost of material is very crucial overall criteria, then aluminum is the cheapest and it is considered over stainless steel.
Having used about 17 properties to draw comparisons between stainless steel and aluminum in chapter 1, we present a summary table below to help you compare and contrast between the two metals.
Stainless steel and aluminum are among the most commonly used metals in the manufacturing space. Their applications in rages from aerospace, medical, culinary, architecture, construction, and many more. While both stainless steel and aluminum are similar, they both possess specific and unique properties. It is, however, more than just cost, the factors or properties explained in this article are very crucial when choosing the right type of metal for your project. If followed, then your project is a successful one.
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