Cast Iron vs Cast Aluminum – How are they different?

As we are probably already aware, cast iron and cast aluminum are two of most widely used metals, both serve different services across millions of different applications in many industries. But both metals are very different from each other, from manufacturing processes, to their unique properties, so how do we tell apart their differences? This article will take a detailed comparison between cast iron vs cast aluminum, hopefully you will learn something by the reading this article.

Contents Overview

What is Cast Iron?

Cast iron is an iron-carbon alloy with a carbon content greater than 2%. It is made by remelting pig iron along with substantial amounts of scrap iron, scrap steel, limestone, carbon (coke), and taking various steps to remove undesirable contaminants. It is poured into molds to make a variety of products. As we have talked about before in our cast iron casting article, there are a few types if cast iron, here is a rewind of the types below:

Common Types

Gray Cast Iron: The most common type, characterized by its flake graphite microstructure, which gives it good damping properties and compressive strength but makes it brittle in tension.
White Cast Iron: Contains carbon in the form of cementite (iron carbide, Fe₃C). It is harder and more brittle due to its microstructure and is often used as a material for wear-resistant surfaces.
Ductile Cast Iron (Nodular Cast Iron): This type has its carbon content in the form of tiny, round nodules of graphite, giving it enhanced ductility and toughness compared to gray cast iron.
Malleable Cast Iron: Made by heat-treating white cast iron to convert the carbides into graphite in the form of irregularly shaped aggregates. It has better ductility than gray and white cast irons.

Basic properties of cast iron

Density: Approximately 6.9 to 7.8 grams per cubic centimeter
Melting Point: Ranges from about 1150 to 1200 degrees Celsius
Typical Uses: Widely used in the automotive industry for engine blocks and cylinder heads, pipes and fittings in the plumbing industry, and for cookware.

Check below table for a detailed comparison between basic properties each type of cast iron

Type of Cast Iron	Density (g/cm³)	Melting Point (°C)
Gray Cast Iron	6.9 – 7.3	1150 – 1200
White Cast Iron	7.0 – 7.7	1150 – 1250
Ductile (Nodular) Cast Iron	7.0 – 7.3	1150 – 1200
Malleable Cast Iron	6.9 – 7.8	1150 – 1200

As you can see. These values provide a general guide to the properties of various cast irons, though specific compositions can slightly alter these figures.

What is cast Aluminum?

What about cast aluminum? Cast aluminum refers to aluminum objects produced by pouring molten aluminum into molds to achieve desired shapes. Aluminum is alloyed with other materials like silicon, copper, magnesium, and zinc to improve its properties.

Common Alloys Used

A356 Aluminum Alloy: Contains silicon and magnesium. It is known for its excellent castability, weldability, and strength.
Alloy 380: An aluminum-silicon blend that is the most commonly used die-cast aluminum alloy, balancing castability with mechanical properties.
Alloy 319: Contains aluminum, silicon, and copper, used for good casting properties and decent strength.

Basic Properties

Density: Typically around 2.7 grams per cubic centimeter, depending on the alloying elements.
Melting Point: Generally ranges from 600 to 660 degrees Celsius, based on the specific alloy.
Typical Uses: Used in a wide range of applications including automotive components such as transmission cases and engine blocks, cookware, and small appliance housings.

As you can see from the below table, both the density and melting point of cast iron are significantly lower than cast iron.

Types of Cast Aluminum	Density (g/cm³)	Melting Point (°C)
A356 Aluminum	Approx. 2.68	615 – 655
Alloy 380	Approx. 2.71	595 – 650
Alloy 319	Approx. 2.79	555 – 630

And because of this property, cast aluminum is cast using different processes compared to cast iron; its lower density also makes cast aluminum lighter; thus it is suitable for different applications compared to cast iron. We will cover these applications later in this article.

Appearance Difference Between Cast Iron vs Cast Aluminum

Can you tell apart cast iron vs cast aluminum just by looking at them? When comparing cast iron vs cast aluminum, the visual differences can be quite noticeable. Cast iron typically has a darker, often grayish color. This is due to its high carbon content, which affects its color and texture. In contrast, cast aluminum usually appears lighter, with a silvery finish because of its primary aluminum composition.

When discussing cast iron vs cast aluminum, another key difference in appearance is the surface texture. Cast iron might display a rougher, more porous surface. This is a result of the casting process and the material’s properties. On the other hand, cast aluminum tends to have a smoother surface which can give it a cleaner, more polished look.

In the battle of cast iron vs cast aluminum, weight is also a visible clue. Though not immediately obvious until you handle the materials, cast iron is significantly heavier than cast aluminum. This weight difference might not be seen but can be felt, adding another layer to their distinction.

So, when you compare cast iron vs cast aluminum, check the color, texture, and weight. These features will help you identify which is which more easily.

Manufacturing Processes Difference Between Cast Iron vs Cast Aluminum

When looking at the manufacturing advantages of cast iron vs cast aluminum, particularly with methods like investment casting, sand casting, shell molding, and die casting, each material showcases unique benefits suitable for different applications.

For both cast iron and cast aluminum, sand casting offers a significant advantage due to its flexibility and cost-effectiveness. This method allows for the creation of large and complex shapes without the high costs associated with other techniques, making it a practical choice for both materials.

Investment casting provides advantages such as excellent surface finish and high dimensional accuracy for both cast iron and cast aluminum. This makes it ideal for producing components that require intricate details and precision, benefiting a wide range of industries from automotive to aviation components.

Shell molding, utilized for both cast iron and cast aluminum, is known for its ability to achieve better surface quality and more complex geometries compared to traditional sand casting. This method is particularly advantageous when tighter tolerances and smoother surfaces are necessary, enhancing the overall quality of the cast components.

Die casting, on the other hand, is a standout process for cast aluminum but not used for cast iron. The main advantage of die casting for cast aluminum includes producing high-volume, complex parts with excellent dimensional accuracy and smooth surfaces at a faster rate. Since cast aluminum has a lower melting point and is less abrasive to molds, it is more suitable for the high-pressure and high-speed environment of die casting.

Below is a comparison table highlighting the advantages of different manufacturing processes for cast iron vs cast aluminum:

Manufacturing Process	Advantages for Cast Iron	Advantages for Cast Aluminum
Sand Casting	Flexible, cost-effective, allows for large and complex shapes	Flexible, cost-effective, allows for large and complex shapes
Investment Casting	Excellent surface finish, high dimensional accuracy	Excellent surface finish, high dimensional accuracy
Shell Molding	Better surface quality, complex geometries, tighter tolerances	Better surface quality, complex geometries, tighter tolerances
Die Casting	Not commonly used	High-volume production, excellent dimensional accuracy, faster production rates, smooth surfaces

This table provides a clear and simple overview of how each process benefits cast iron and cast aluminum, focusing on the specific advantages applicable to each material.

Mechanical Properties Comparison Between Cast Iron vs Cast Aluminum

When comparing the mechanical properties between cast iron vs cast aluminum, we can see that each material showcases unique characteristics, making them suitable for specific uses based on their weight, heat conductivity, corrosion resistance, strength, and other vital properties.

Weight

Starting with weight, cast aluminum is notably lighter than cast iron. This makes cast aluminum an attractive choice for industries where reducing overall weight is beneficial, such as in automotive or aerospace manufacturing. The lightweight nature of cast aluminum simplifies handling and transportation, and it contributes to better fuel efficiency in vehicles.

Heat Conductivity

Moving on to heat conductivity, cast aluminum is superior to cast iron. Aluminum’s ability to conduct heat quickly and efficiently makes it perfect for applications such as cooking utensils and radiators, where quick heat distribution is crucial. Cast iron, while slower to heat up and cool down, retains heat for longer periods, which is why it’s often used for pans and stoves.

Corrosion resistance

In terms of corrosion resistance, cast aluminum again has the upper hand over cast iron. Aluminum forms a natural oxide layer when exposed to air, which protects it from further corrosion. This trait is particularly valuable for products used outdoors or in corrosive environments. Cast iron, however, will rust and degrade unless it’s properly treated or painted, requiring more maintenance over its lifespan.

Strength

Discussing strength, cast iron typically displays greater compressive strength and hardness, making it suitable for heavy-duty applications. It’s commonly used in construction for support beams or pipes where high strength is essential. However, it’s more brittle and can crack under stress or shock, unlike cast aluminum, which, though softer, offers more flexibility and less risk of cracking under impact.

Ductility

Ductility is another aspect where cast aluminum shines over cast iron. The malleability of aluminum allows it to be used in designs that require intricate shapes and fine details without risking fractures during the casting process.

Wear Resistance

Finally, let’s touch on wear resistance. Cast iron, particularly white cast iron, is often used in surfaces that undergo high levels of friction and wear, such as in grinding machines and milling equipment, due to its hardness and ability to withstand wear.

Mechnical Properties Comparison Table

Check out this detailed comparison table that outlines the key mechanical properties of cast iron vs cast aluminum:

Property	Cast Iron	Cast Aluminum
Weight	Heavier, adding to sturdiness and stability	Lighter, enhancing ease of handling and efficiency
Heat Conductivity	Lower, retains heat longer, suitable for applications needing heat retention	Higher, dissipates heat quickly, ideal for applications requiring rapid heat transfer
Corrosion Resistance	Prone to rust unless treated, requires more maintenance	Naturally corrosion-resistant, requires less upkeep
Strength	High compressive strength and hardness, ideal for structural applications	Softer, less strong in compression but more adaptable to impact and stress
Ductility	Brittle, low ductility, can crack under stress	High ductility, can be cast into complex shapes without cracking
Wear Resistance	Excellent wear resistance, suitable for high-wear environments	Lower wear resistance, not ideal for high-friction applications unless alloyed with other metals

This table concisely captures the mechanical properties comparison between cast iron vs cast aluminum, showcasing how each material is suited to different applications based on their specific characteristics.

Application Comparison Between Cast Iron vs Cast Aluminum

When comparing cast iron vs cast aluminum in various industries, the distinction in their applications is influenced significantly by their properties. Here’s a simple breakdown of how cast iron castings and aluminum alloy castings are used across at different industries.

Automotive Industry:

Cast Iron Parts: Used for manufacturing heavy-duty engine blocks, brake rotors, and gear components due to the high strength and wear resistance of cast iron.
Aluminum Components: Predominantly used for making lighter engine parts like pistons, cylinder heads, and transmission housings, helping in reducing vehicle weight and improving fuel efficiency.

Construction and Infrastructure:

Cast Iron Components: Employed in the production of pipes, manhole covers, and architectural elements because of their durability and compressive strength.
Aluminum Castings: Used in constructing window frames, panels, and structural components where light weight and resistance to corrosion are paramount.

Cookware and Kitchen Appliances:

Cast Iron Castings: Ideal for skillets, pans, and cooking pots due to excellent heat retention and distribution.
Aluminum Alloy Castings: Commonly used for lighter, non-stick cookware and kitchen tools that require good thermal conductivity.

Aerospace Industry:

Cast Iron Parts: Less commonly used but found in specific applications requiring high wear resistance.
Aluminum Parts: Essential for aircraft frames, panels, and jet engine components because of their lightweight and ability to withstand high pressures and temperatures.

Energy Sector:

Cast Iron Components: Used in wind turbine housings and oil drilling equipment for their robustness and longevity.
Aluminum Components: Aluminum is preferred for solar panel frames and components of electrical transformers due to its corrosion resistance and lightweight.

Marine Industry:

Cast Iron Castings: Suitable for ballast weights and heavy-duty marine fittings.
Aluminum Alloy Parts: Favored for ship structures, hulls, and deck components to reduce overall mass and enhance corrosion resistance against harsh marine environments.

Foundry and Manufacturer Equipment:

Cast Iron Parts: Used in the manufacturing of heavy machinery and foundry tools.
Aluminum Castings: Often selected for machinery components that require lightweight and rust-resistant properties in a foundry or manufacturing setting.

Rail Industry:

Cast Iron Components: Used in making braking systems and track parts due to the need for heavy, robust materials.
Aluminum Alloy Castings: Utilized in railcar frames and interior components for reducing the weight of trains, thus enhancing speed and energy efficiency.

These examples illustrate how cast iron vs cast aluminum are selected based on specific industry requirements. While cast iron offers great strength and heat endurance, aluminum alloy parts provide advantages in weight reduction and corrosion resistance, making them ideal for different applications within these sectors. This comparison underlines the importance of choosing the right material—cast iron castings or aluminum castings—depending on the performance criteria and environmental conditions each industry faces.

How Should You Choose Between Cast iron and Cast Aluminum for Your Project

Choosing between cast iron and cast aluminum for your project involves understanding the key differences and strengths of each material. Here’s a straightforward guide on how to decide between cast iron vs cast aluminum, make sure you select the right material for your specific needs.

Consider the Weight Requirements:

If your project requires lightweight components, cast aluminum is the better choice due to its significantly lower weight compared to cast iron. This is crucial in industries like aerospace or automotive, where reducing weight can enhance performance and fuel efficiency.
For projects where weight adds stability and durability, such as in construction or machinery, cast iron may be preferable.

Evaluate the Working Environment:

Cast aluminum is highly resistant to corrosion, which makes it suitable for use in environments that are moist or corrosive. For outdoor furniture, marine applications, or any project exposed to harsh weather, aluminum components are ideal.
Cast iron, while robust, does require protective coatings to prevent rust when exposed to moisture, making it less suitable for outdoor or marine environments without proper treatment.

Assess the Mechanical Stress:

Cast iron offers superior strength under compression, making it excellent for supporting structures in construction or heavy-duty machinery. If your project involves heavy loads or needs to withstand significant stress, cast iron is likely the better option.
Cast aluminum, while not as strong as cast iron, provides enough strength for many applications and is preferable when the material must also be ductile and malleable. This makes it ideal for automotive parts and small components that need to be intricately shaped.

Review Thermal Requirements:

For projects requiring good heat conductivity, such as heat sinks or cookware, cast aluminum is advantageous because it conducts heat quickly and evenly.
If your project benefits from heat retention, such as in cooking pans or radiators, cast iron’s ability to retain heat might be more beneficial.

Budget Constraints:

Generally, cast aluminum can be more expensive than cast iron due to the cost of raw materials and the casting process involved. Consider your budget and how it aligns with the material costs and the production methods (like die casting for aluminum).

Longevity and Maintenance:

Think about the longevity and maintenance of the material. Cast iron, if maintained properly, can last a very long time but does require regular care to prevent rust and deterioration.
Aluminum is low maintenance and does not rust, which might reduce long-term upkeep costs.

Making Your Decision

The choice between cast iron and cast aluminum depends on the factors we’ve mentioned throughout the article, including differences in appearance, properties, manufacturing processes, applications, and simple guidance on how to choose between them. Ultimately, the decision is yours. However, the best material for your needs might not always be apparent. If that’s the case, just let us know. Taiyuan Simis is a professional precision casting foundry specialized in various casting methods like investment casting, sand casting, shell molding, and die casting.

We also provide in-house tooling and machining to accommodate each process. And it goes without saying that we offer heat treatment, surface treatment, shipping and tracking, as well as comprehensive guidance and support to help you achieve your project goals. We are a complete package, so if you have any questions about which material to choose or which processes you are uncertain of, please be sure to contact us without hesitation.