In recent years, the market has seen a surge in lightweight materials, but one material has consistently remained popular: aluminum. What makes aluminum so desirable? What are its advantages? And when it comes to aluminum machining, especially milling, what pitfalls should you be aware of? Read our overview to find out!

This article analyzes the topic from the following six aspects:

1. Characteristics of Aluminum

2. Mechanical Properties of Aluminum

3. Categories of Aluminum Forging Materials: The Key to Successful Machining

4. Challenges in Aluminum Machining

5. Is Cutting Fluid Necessary When Milling Aluminum?

6. Feed Rates and Cutting Speeds for Aluminum

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01. Characteristics of Aluminum

Aluminum is indispensable in industrial production. This is mainly due to its unique properties:

• Lightweight: In automotive and aerospace industries, aluminum helps reduce weight and fuel consumption.

• Stable: Thanks to various alloying elements, aluminum’s tensile strength can almost match that of steel.

• Good conductor: Its high thermal conductivity and specific heat make it suitable for machining at high cutting speeds.

• Resource-saving: Aluminum is ideal for recycling.

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02. Mechanical Properties of Aluminum

Aluminum, a non-ferrous metal with the chemical symbol Al, is widely used as a structural material in electrical engineering, packaging, and construction. Compared with other metals, aluminum is lighter, more electrically conductive, and has better thermal performance—key factors in its application.

Aluminum is soft and light yet tough. Its melting point is 660.4°C, much lower than other metals, and its density is 2.70 g/cm³, about one-third that of steel. The tensile strength of aluminum depends on its purity: pure aluminum has a tensile strength of 45 N/mm², while commercial pure aluminum can reach up to 90 N/mm². Its thermal conductivity is 237 W/(m·K), higher than most base metals, second only to silver, copper, and gold. High thermal conductivity makes aluminum widely used in electrical engineering. Its physical properties also make it an excellent conductor, often used in energy technologies as a large cross-section conductor, replacing copper.

When exposed to air, aluminum quickly forms an oxide layer. This gives unprocessed aluminum a silver-gray, slightly dull appearance. The oxide layer is about 0.05 μm thick, providing excellent corrosion resistance and preventing further oxidation.

Depending on the application, aluminum can be used in pure or alloyed form. By melting with other metals, certain properties of this lightweight metal can be enhanced or suppressed. Aluminum alloys are produced as casting or forging alloys, mainly using manganese, magnesium, copper, silicon, nickel, zinc, and beryllium. The base material is usually Al99.5 (EN AW-1050A).

There are distinctions between heat-treatable and non-heat-treatable aluminum alloys, as well as between forged and cast aluminum alloys. Naturally hardening aluminum alloys (e.g., AlMg), as well as pure and ultra-pure aluminum, belong to forged aluminum alloys. Heat-treatable alloys (e.g., AlMgSi, AlCuMg, or AlCuSiMn) also belong to forged alloys, suitable for producing semi-finished products such as strips, sheets, wires, or tubes.

Adding small amounts of copper, nickel, zinc, silicon, manganese, or magnesium can produce forged alloys with higher hardness and tensile strength, though electrical conductivity decreases. These alloys are still machinable, making them ideal for ships, aircraft, or transport containers.

The most important casting aluminum alloy is the aluminum-silicon eutectic alloy, with about 12% silicon. Its very low viscosity maintains high tensile strength while ensuring excellent casting properties. As a result, it has a long history in automotive and aerospace components such as gearboxes and motor housings.

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03. Categories of Aluminum Forging Materials: The Key to Successful Machining

Unfortunately, not all aluminum alloys and related materials have the same machinability. For example, pure aluminum is very soft and, due to low tensile strength, difficult to machine. These materials significantly affect chip shape, tool wear, surface finish, and cutting forces. Therefore, categorizing aluminum forging materials into three classes has proven useful.

1st Class Aluminum Forging Materials
These include low-tensile-strength alloys, such as non-hardened or partially solidified alloys like the 1000 series, 5005A, and 5454. Also included are non-hardened forms of heat-treatable alloys such as EN AW-6063, 6060, and 6082. Due to low tensile strength, machining often causes chip adhesion and a “smearing effect,” leading to more severe built-up edge (BUE). Using appropriate cutting fluids is recommended to minimize BUE formation.

2nd Class Aluminum Forging Materials
These materials have higher tensile strength. This includes non-hardened materials in work-hardened conditions, such as 5000 series alloys, and heat-treatable materials in hardened states, such as 6000 and 7000 series alloys. Their tensile strength ranges from 300–600 N/mm², with no hard inclusions, resulting in minimal wear. Higher tensile strength also reduces BUE formation.

3rd Class Aluminum Forging Materials
This class includes free-machining alloys with lead or bismuth as chip-breaking additives, such as EN AW-2011, 2007, or 6012. These alloys produce short chips that are less prone to BUE formation.

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04. Challenges in Aluminum Machining

Although aluminum is generally considered easy to machine, it still faces challenges. Chip adhesion and built-up edge are the most troublesome issues during milling. A successful approach combines proper cutting fluid strategies with high-speed machining (HSC) and suitable tools. Cutting forces are roughly one-third of those for steel.

The primary goal when milling aluminum is to quickly remove chips from the cutting zone. Smooth, low-friction milling cutters help evacuate sticking aluminum chips. Compared to steel cutters, aluminum cutters have fewer teeth, aiding chip evacuation. Specially optimized coatings can also improve chip removal.

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05. Is Cutting Fluid Necessary When Milling Aluminum?

During aluminum milling, cutting fluid not only provides cooling but also lubricates, minimizing wear and frictional heat. Cooling is particularly important because aluminum has greater thermal expansion than steel. Proper heat dissipation improves dimensional accuracy. Emulsified micro-lubricants composed of water and cutting oil have proven highly effective for cooling and lubrication.

Ethanol is also recommended in aluminum milling for cooling chips and preventing clogging. Oil-free fluids make chips easier to blow away, collect, and recycle.

If cutting fluids are not desired or prohibited, DLC (diamond-like carbon) coatings are an excellent alternative. These high-performance coatings allow even dry machining, making the machine operate as if lubricated. Aluminum’s properties help here as it dissipates heat more easily than steel.

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06. Feed Rates and Cutting Speeds for Aluminum Milling

A simple rule for successful aluminum milling: higher cutting speeds yield smoother surfaces, but this also increases tool wear. High-speed cutters (HSC) operate at speeds far exceeding conventional cutters.

Hard aluminum alloys are best suited for milling at cutting speeds of 100–500 m/min, depending on cutter diameter and feed rate. For cutter diameters of 2–4 mm, feed per tooth is 0.02–0.03 mm; for 5–8 mm, feed increases to 0.05 mm; for 9–12 mm, feed rises to 0.10 mm. Hard aluminum alloys are machined at 100–200 m/min, with feed rates similar to soft aluminum.