Types of Aluminum Alloys: A Practical Guide for CNC Machining

What Are Aluminum Alloys?

Aluminum alloys are materials produced by mixing pure aluminum with one or more other alloying elements, such as copper, magnesium, silicon, zinc, or manganese. The purpose of alloying aluminum is to improve the metal’s mechanical, thermal, and chemical properties, including potential increases in strength, hardness, corrosion resistance, and thermal conductivity. At the same time, it also aims to preserve aluminum’s natural benefits, such as light weight and good formability.

Pure aluminum alloy is relatively soft and ductile. Aluminum alloys, however, can be specifically tailored for different engineering applications. For example, aluminum-copper alloys are strong but may have low corrosion resistance. In contrast, other aluminum grades offer good corrosion resistance and are well-suited for marine components or aircraft fuel tanks.

Components of Aluminum Alloys

Below are the major components of different types of aluminum alloys:

Copper (Cu)

Copper contributes significantly to the enhancement of aluminium’s strength and hardness when subjected to heat treatment. Aluminum-copper alloys, represented in the 2000 series, are characterized by a high strength-to-weight ratio, making them popular in the aerospace industry. Consequently, aluminum-copper alloys typically exhibit poor corrosion resistance, often requiring protective coatings or anodizing.

Magnesium (Mg)

Magnesium provides enhanced corrosion resistance, weldability, and strength without a substantial increase in weight. Aluminum-magnesium alloys, 5000 cast aluminum series alloys, are known for their corrosion resistance and are prevalent in marine applications, fuel tanks, and pressure vessels.

Silicon (Si)

Silicon improves the fluidity and castability of alloys, making it essential in cast aluminum alloys, 4000 and 6000 series. When used in conjunction with magnesium (Mg), the combination forms magnesium-silicide (Mg₂Si), which enables heat-treatable alloys that have excellent mechanical properties and excellent corrosion resistance.

Manganese (Mn)

Manganese improves strength through strain hardening and increases resistance to different forms of failure. In the non-heat treatable alloys, 3000 series alloys, it is an important alloying element, used extensively in sheet metal fabrication, automotive body panels, and heat exchangers.

Zinc (Zn)

Zinc adds significant strength to heat-treatable alloys (7000 series), typically combined with magnesium and copper. Alloys containing zinc are utilized in aircraft components, structural applications, and sporting equipment. However, alloys containing zinc will suffer from stress corrosion cracking if treated incorrectly.

Iron (Fe)

Iron is usually present as an impurity in aluminum alloys; however, controlled amounts can improve strength and wear resistance. Nevertheless, an excess of iron in an aluminum alloy can decrease both ductility and corrosion resistance.

Other metal alloying elements, which include chromium (Cr), titanium (Ti), or nickel (Ni), can be alloyed in small amounts for grain structure improvement, fatigue resistance improvement, or high-temperature performance.

Properties of Aluminum Cast Alloys

Here are the common properties of aluminum alloys:

• A high strength-to-weight ratio: Aluminium alloys are lightweight yet strong, making them excellent for aeronautical, automotive, and structural applications that require strength and light weight.
• Excellent corrosion resistance: Most aluminium alloys produce a thin layer of aluminium oxide, which protects them against corrosion. Series magnesium and silicon alloys are highly resistant to corrosion, particularly in maritime conditions.
• Good thermal and electrical conductivity: Aluminium alloys have good thermal and electrical conductivity, making them useful in heat exchangers, electrical conductors, and cooling systems.
• Ductility and formability: They are easily moulded, rolled, or extruded into a variety of shapes without breaking, making them ideal for sheet metal manufacturing and complex structural components.
• Recyclability: Aluminium alloys are completely recyclable without losing mechanical qualities, which promotes sustainable manufacturing and reduces environmental impact.
• Good machinability and weldability: Certain aluminium grades have great machinability, making them ideal for CNC machining and welded assemblies with little material loss.
• Heat treatable: Many alloys are heat treatable, which allows producers to improve their tensile strength, hardness, and fatigue resistance via regulated heat treatment techniques.

Different Grades of Aluminum Alloys

There are different grades of aluminum alloys with each having its unique pairings, proportions, and digit combination:

1xxx Series

1XXX Series Alloy comprises at least 99% pure aluminium. Because of their purity, 1XXX series aluminium alloys are highly corrosion resistant but sensitive to high temperatures. Furthermore, the purest alloys from the 1XXX class are commonly used in food packaging and electrical applications.

2xxx Series

The 2XXX Series Alloy is a combination of aluminium and copper, providing higher strength but lower corrosion resistance. Heat treatment of these alloys improves the strength of aluminium over time. Stronger alloys, such as Alloy 2024-T351, are widely used in aeroplanes and the aerospace sector.

3xxx Series

The 3XXX Series Alloy is the most common alloy available. When manganese and aluminium are combined, the result is a highly malleable substance with exceptional heat tolerance. Alloy 3004, a moderately robust and workable alloy, is commonly used in aluminum cans for beverages. Furthermore, 3XXX Series Alloys are well-suited to the manufacture of consumer and electrical items.

4xxx Series

The 4XXX Series Alloy adds silicon to aluminium, resulting in a highly ductile product with a narrow melting range. While this combination lowers the melting point, 4XXX alloys maintain strength throughout the process. These alloys, particularly Alloy 4043, are widely utilised in the automotive and construction industries. Other typical applications for this alloy include decorative architecture and die casting.

5xxx Series

The 5000 Series Alloy combines magnesium and aluminium to create a strong and durable alloy. Alloys in this class are commonly used in marine manufacturing, structural engineering, and the automobile industry. Furthermore, alloys 5052 and 5182 are commonly utilised in the production of aluminium cans for the beverage industry.

6xxx Series

The 6xxx Series Alloy combines aluminium, magnesium, and silicon to create the most flexible and ductile alloy in the series. Furthermore, this mix of materials makes these alloy types strong and resistant to corrosion. Alloys like 6061 have a higher delicacy, making them perfect for the production of truck and boat parts.

7xxx Series

7000 Series Alloy is a zinc and aluminium alloy that has strong stress resistance and great heat reactivity. Alloys such as 7050 and 7075 are ideal for the aircraft sector.

Classification of Aluminum Alloys

Aluminum alloys are generally divided into two major categories.  However, this depends on how they are produced and processed.

Wrought Aluminum Alloys

Wrought aluminum alloys are formed by mechanical processing, primarily rolling, extrusion, or forging. They possess a high strength-to-weight ratio, good formability, and superior corrosion resistance. They are often used in the aerospace, automotive, and construction industries.

Wrought aluminum series are classified by a four-digit numbering system from the series 1xxx to 7xxx (e.g., 6061 or 7075). Each of these series is based on the primary alloying element (e.g., copper, magnesium, silicon, or zinc).

Cast Aluminum Alloys

Cast aluminum alloys are produced by pouring molten aluminum into molds to create complex shapes. Cast aluminum alloys typically have lower tensile strength but better fluidity and are more cost-effective than wrought alloys.

Cast aluminum alloys are commonly used for automotive engine components, pressure vessels, and structures. Cast aluminum alloys are classified based on the series of the primary alloying elements, e.g., silicon, magnesium, and copper, that are added in the CNC manufacturing process.

Common Types of Aluminum Alloy Used in Machining

Here are the common aluminum alloys used in the aluminum CNC machining process:

Aluminum 6061

Aluminium 6061 consists primarily of silicon and magnesium. It is suitable for a variety of applications due to its strength, corrosion resistance, weldability, and heat treatability. It is well-suited to the extrusion technique, and T6 tempering improves its strength and durability. Similarly, it works well with anodising for a more visually appealing finish.

Aluminum 7075

The 7075 aluminium alloy is a robust alloy with comparable strength to steel. The principal alloying components are copper and zinc. It is used in applications that require a high level of strength, such as spacecraft and aircraft. Although not weldable, it is robust, relatively weldable, and can sustain stress.

Aluminum 5052

Aluminium 5052 is a dependable alloy with high corrosion resistance and moderate strength. The alloy’s lack of copper content makes it ideal for marine applications. Marine equipment is the most prevalent application for 5052 aluminium. However, because the 5052 is made of 5xxx aluminium alloy, it cannot be heat-treated.

Aluminum 6063

Aluminium 6063, often known as architectural aluminium, is a magnesium-silicon alloy with moderate strength and good flexibility. It is very compatible with die formation. Furthermore, the magnesium-silicide makeup of aluminium 6063 makes it very corrosion-resistant.

Architectural objects, furniture, pipelines, and other items are among the most popular parts made from 6063 aluminium. This grade of aluminium can also be laser etched.

Common Applications of Aluminum Grade Alloys

Below are some of their most common applications:

Aerospace Industry

Aluminum alloys are critical in the aerospace industry when making aircraft parts, including fuselages, wings, and landing gear. Their high strength-to-weight ratio and fatigue resistance make them a good fit for strength and lightweight demands.

Automotive Industry

Aluminum alloys can be found in many automotive parts like body panels, truck wheels, engine blocks, and fuel tanks. They improve fuel economy because of the reduced weight of the vehicle without compromising structural integrity and crash performance.

Construction and Architecture

Aluminum alloys are used in aluminum alloys for structural components and facades, as well as roofing systems and window frames. Their corrosion resistance and aesthetic appeal are great for both interior and exterior architecture.

Marine Applications

Certain aluminum alloys are used in marine applications such as boat hulls, decks and offshore structures due to their corrosion resistance. They can withstand saltwater exposure and other environmental conditions that will allow them to perform for several years.

Factors to Consider When Selecting an Aluminum Alloy

Here are key factors to consider when selecting an aluminum alloy for your needs:

Strength Specifications

Strength specifications differ depending on the project, as heat-treatable alloys, such as those in the 2000, 6000, and 7000 series, are best for high-strength designs, like aerospace or automotive structures, while non-heat-treatable alloys, such as 1000 or 3000 series, are good for general-purpose and light structural designs.

Corrosion Resistance

Alloys with high corrosion resistance, such as the 5000 and 6000 series, are preferred for use in marine environments or construction or outdoor environments, and copper-containing alloys (2000 series) have relatively low corrosion resistance and often need surface protection by anodizing or powder coating.

Thermal and Electrical Conductivity

Alloys with high thermal conductivity, such as the 1000 series, are best for heat exchangers and electrical conductors, and all alloying elements reduce conductivity, with a purer alloy being more conductive for electrical applications.

Cost and Availability

Cost and Availability Last, you should consider the cost and availability of specific alloys. Some high-performance alloys offer exceptional strength or corrosion resistance, but these alloys come at an expense. Ultimately, for each project, the ideal balance must satisfy the performance, cost and manufacturability considerations.

Conclusion

Aluminium alloys are valued for their lightweight, high strength, corrosion resistance, and versatility, making them an ideal choice for companies in aerospace, automotive, and construction. Knowing the alloys and their properties helps you decide what is best suited for your application. At AT Machining, we offer CNC precision machining, and machining increases aluminum parts, providing tightly held tolerances and high-quality surface finishes. Contact us to get reliable, high-performance aluminum parts for your next project.