Know Your Metals: Aluminum

October 23, 2020 10:48 am

Aluminum and its alloys are highly popular in the machining industry for many reasons. Did you know it is the most abundant metal on Earth? That’s why it is such a cost-effective option. Aluminum is also desired for its physical properties. It is a great option when considering machinability, corrosion resistance, appearance, and recyclability.

Let’s take a more in depth look at the qualities of the material that make it suitable for a variety of applications and industries.

Physical Properties

Aluminum’s strength to weight ratio is unique, highly impressive and a core benefit when machining the material. It can be surprising how strong the metal is, considering how lightweight it is. This quality is what makes aluminum suitable for use in the aerospace and automotive industries.

Another quality, adding to aluminum’s popularity, is its resistance to corrosion. Aluminum develops an oxide layer to fully protect against corrosion. This “oxide skin” makes the metal resistant not only to weathering, but also to many (not all) acids.

Aluminum is also considered “easy” to machine. CNC machines and aluminum are compatible because the metal is pliable, so it chips easily. This allows the machines to cut quickly and accurately. That is not to say that aluminum comes without challenges as the machinability of aluminum varies depending on the alloy and grade.

Aluminum Grades and Alloys

The various grades and alloys have different physical properties. Different elemental chemistries are intentionally controlled to manipulate the metal’s microstructure and composition. This is done to enhance certain characteristics in order to satisfy various application/design needs.

There are many aluminum alloys and grades, but they can be split into two main groups: cast aluminum and wrought aluminum. What differentiates these two categories is the manufacturing processes used to develop them.

Cast Aluminum

Cast aluminum is melted and then poured into a mold. It has larger percentages of alloying elements than wrought aluminum. Due to its low tensile strength and flexibility, cast aluminum is most often used for making machine tools, engine cylinder heads, gearbox housing, cast wheels and more. It is also the cheaper option when compared to wrought aluminum.

See the image below for a breakdown of the different cast aluminum grades and Information about their properties.

Image Credit: https://www.thomasnet.com/articles/metals-metal-products/types-of-aluminum/

 

Wrought Aluminum

After the smelting process, the alloy is manipulated either by being rolled, forged, or extruded into a final shape. Due to its higher tensile strength, wrought aluminum is most frequently used in extrusions, aircraft frames, pressure vessels and more. With wrought aluminum, you can expect better surface finishes and structural integrity as opposed to cast aluminum.

See the image below to for breakdown of the different wrought aluminum grades and information about their properties.

Image Credit: https://www.thomasnet.com/articles/metals-metal-products/types-of-aluminum/

Challenges of Machining Aluminum

Similar to other metals, the physical properties that make aluminum suitable for machining can also cause some less than desirable qualities.

Because of aluminum’s soft nature, it is common for gummy buildup to form. This occurs because of the metals low melting point. If you can, choose an aluminum alloy that has been tempered for hardness. This helps manage the heat friction to prevent the material from fusing to the cutting edge.

Deformation of the part is also common due to the relatively low hardness and high thermal expansion quality of the metal. This pertains mainly to the machining of thin parts.

Tips for Machining Aluminum

Good practices will ensure successful machining with aluminum. Make sure to select the right cutting parameters. For best results, you should optimize toward high cutting speeds and invest in very hard and sharp cutting tools. Reducing back cutting depth is always important as it highly impacts cutting force. By reducing the back cutting depth and increasing the speed this will reduce the overall cutting force.

As mentioned above, deformation is a frequent challenge when machining aluminum. To avoid deformation, it is important avoid extreme concentration of heat. This can be achieved through symmetrical machining which reduces the rate of thermal deformation.

Recommended Reads

As a machinist, it is imperative that you understand the properties of different metals. The better you understand the material you are machining, the more equipped you are to select the right tools and parameters for the application. Here are some resources to expand your knowledge of aluminum.

Handbook of Aluminum: Volume 2: Alloy Production and Materials Manufacturing

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This reference provides a thorough and in-depth coverage of the latest production and processing technologies encountered in the aluminum alloy industry. It also includes information about current analytical methods for aluminum alloy characterization as well as extractive metallurgy, smelting, master alloy formation, and recycling.

Aluminum Recycling

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What makes this book unique is its specific focus on aluminum recovery, rather than just recycling in general. It offers an integrated discussion of scrap recovery and re-melting operations and includes economic as well as technical elements of recycling. This book also covers other topics such as the scrap aluminum marketplace, how secondary aluminum is collected and sorted, the refining of molten aluminum, and the recovery and processing of dross from re-melting operations.

Properties of Aluminum Alloys: Tensile, Creep, and Fatigue Data at High and Low Temperatures

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This book includes more than 300 tables that detail the typical properties of a wide range of aluminum alloys. It also includes information about the mechanical properties and fatigue strength of wrought and cast aluminum alloys at various temperatures.

Encyclopedia of Aluminum and Its Alloys

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This encyclopedia is a comprehensive reference covering all major aspects of metallurgical science and engineering of aluminum and alloys. Topics covered include extractive metallurgy, powder metallurgy(including processing), physical metallurgy, production engineering, corrosion engineering, thermal processing (processes such as metalworking and welding, heat treatment, rolling, casting, hot and cold forming), and many more.

Fundamentals of Aluminum Metallurgy: Production, Processing and Applications

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This book is a standard reference for researchers in metallurgy, as well as all those involved in the manufacture and use of aluminum products. Part one discusses different methods for producing and casting aluminum, quality issues and specific production methods such as high-pressure diecasting. Part two covers the metallurgical properties of aluminum and its alloys and part three includes chapters on joining, laser sintering and other methods of processing aluminum.

Aluminum Alloy Castings: Properties, Processes and Applications

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This text provides property and performance data for all types of aluminum alloy castings and reviews the factors that contribute to and affect those properties including composition, microstructure, casting process, heat treatment, and quality assurance of aluminum.

Features of Aluminum Alloy Parts Processing on CNC Machines

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This book focuses on the features of processing of aluminum alloy blanks on CNC machines, In particular,: a literary review of aluminum alloys and their characteristics, the scope of application and main features, the basic calculations of cutting modes, characteristics of coolant and their role in aluminum applications, and the consequences of improper operation of coolant in CNC machine tools.

Machining of Light Alloys: Aluminum, Titanium, and Magnesium

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This book is a comprehensive source on the machining of light alloys, presenting a collection of both experimental and review studies. The work is arranged in eight chapters, presented by a group of international scholars, which analyze the main problems related to the machining of these alloys from different perspectives.

 

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