Aluminum Alloy Hardness Chart: HW, HB, HV, HRB, HBA

Introduction

Definition of Aluminium Hardness

Hardness in aluminium refers to the material’s ability to resist localized plastic deformation, which can occur due to indentation, abrasion, or penetration. This property is crucial for understanding how aluminium alloys will perform under various mechanical stresses and conditions. Hardness is a significant parameter that influences the durability, wear resistance, and overall mechanical performance of aluminium alloys.

Importance of Hardness in Aluminium Alloys

The hardness of aluminium alloys is a key factor in determining their suitability for different applications. It directly affects the material’s resistance to wear and tear, its ability to hold shape under mechanical stress, and its overall longevity in service. For instance, higher hardness values in aluminium alloys are desirable in applications where abrasion resistance and structural integrity are critical, such as in aerospace and automotive components.

Hardness also correlates with other mechanical properties, such as tensile strength and yield strength, making it a vital consideration in the material selection process. Understanding the hardness of aluminium alloys helps engineers and manufacturers ensure that the chosen material will meet the performance requirements of specific applications, enhancing safety, reliability, and efficiency.

Measurement of Hardness in Aluminium Alloys

Hardness in aluminium alloys can be measured using several different methods, each with its own relevance and application. The most common methods include Brinell, Rockwell, and Vickers hardness tests.

• Brinell Hardness Test: This method involves pressing a hard steel or carbide ball into the material under a specific load. The diameter of the indentation left in the material is measured, and the hardness value is calculated. Brinell hardness numbers (BHN) are commonly used for softer aluminium alloys.
• Rockwell Hardness Test: The Rockwell test measures the depth of penetration of an indenter under a large load compared to the penetration made by a preliminary load. The Rockwell hardness number (HR) is derived from the depth difference. This method is quicker and more straightforward, suitable for a wide range of aluminium alloys.
• Vickers Hardness Test: This method uses a diamond pyramid indenter and applies a specific load to create an indentation. The size of the indentation is measured microscopically, and the Vickers hardness number (HV) is calculated. The Vickers test is highly accurate and can be used for both hard and soft aluminium alloys.

For example, the 6061 aluminium alloy typically has a Brinell hardness of around 95 BHN, while the 7075 aluminium alloy, known for its high strength, has a Brinell hardness of approximately 150 BHN. These values illustrate how different aluminium alloys can vary significantly in hardness, influencing their application.

Factors Influencing Hardness in Aluminium Alloys

Several factors influence the hardness of aluminium alloys, including alloying elements, heat treatment, and work hardening.

Work Hardening: The process of deforming the aluminium alloy at room temperature can increase its hardness. Cold working, such as rolling or hammering, introduces dislocations in the material’s crystal structure, making it harder and stronger.

Alloying Elements: Elements such as copper, magnesium, silicon, and zinc are added to aluminium to enhance its mechanical properties, including hardness. For instance, the addition of zinc in the 7075 aluminium alloy significantly increases its hardness and strength.

Heat Treatment: Heat treatment processes, such as solution heat treatment and aging, can alter the microstructure of aluminium alloys, thereby affecting their hardness. For example, the T6 tempering process for 6061 aluminium involves solution heat treatment followed by artificial aging, resulting in improved hardness and mechanical properties.

Aluminum Alloy Hardness Chart

The table below provides typical Vickers hardness values measured with a Tianxing W-20 Vickers hardness tester for nearly 400 different grades of aluminum alloy materials with different heat treatment processes.

The Vickers hardness values in the table are actual measured typical hardness values of various aluminum alloy materials and are not used as the basis for whether the material is qualified. The hardness qualification values for various materials should refer to the corresponding product technical specifications. For example, it is stipulated in the national standard GB 5237.1 “Aluminum Alloy Building Profiles Part 1: Base Material” that the Vickers hardness value of 6063-T5 should not be less than 8HW, and the Vickers hardness value of 6063A-T5 should not be less than 10HW.

The Brinell hardness, Vickers hardness, Rockwell hardness, and Barcol hardness are for reference only and cannot be used for conversion. If conversion is required, it is recommended to use the hardness conversion table of the American standard ASTM E140.

Aluminum Alloy Hardness Chart

Comparative Analysis

Comparison of Hardness Across Aluminium Alloys

Methodology for Comparison

Conducting a comparative analysis of aluminium hardness involves evaluating various factors such as alloy type, temper, and the presence of reinforcing materials. The comparison is typically based on standardized hardness testing methods like Rockwell, Brinell, and Vickers. These tests provide quantifiable measurements that can be used to compare different alloys’ hardness levels under similar conditions.

Factors Influencing Hardness

Several key factors influence the hardness of aluminium alloys:

1. Alloying Elements:
   • Copper (Cu): Enhances hardness and strength. For example, alloy 2024, which contains copper, is known for its high strength and hardness, making it suitable for aerospace applications.
   • Magnesium (Mg): Contributes to moderate hardness and corrosion resistance. Alloy 5052, which contains magnesium, is used in marine environments due to its good corrosion resistance and moderate hardness.
   • Silicon (Si): Improves casting properties and moderate hardness. Casting alloy 356, which contains silicon, is commonly used in automotive parts for its good casting characteristics and sufficient hardness.
   • Zinc (Zn): Increases hardness and strength significantly. Alloy 7075, containing zinc, is one of the strongest aluminium alloys, used in applications requiring high strength like aircraft structures.
2. Heat Treatment Processes:
   • Solution Heat Treatment: Involves heating the alloy to dissolve alloying elements, followed by rapid cooling to create a supersaturated solution. This process enhances the hardness of alloys like 6061 and 7075.
   • Aging: Both natural and artificial aging processes allow the formation of precipitates, increasing hardness. For example, the T6 temper involves solution heat treatment followed by artificial aging, which enhances hardness in alloys like 6061-T6 and 7075-T6.
3. Natural Aging: Over time, aluminium alloys naturally age, leading to changes in hardness due to the slow formation of precipitates. This process can be accelerated through artificial aging treatments.
4. Reinforcing Materials: Adding materials like zirconium diboride or snail shells to aluminium matrices can increase hardness and elastic modulus. The reinforcement percentage directly correlates with the composite’s hardness and mechanical properties.

The factors influencing hardness play a crucial role in determining the suitability of an aluminium alloy for specific applications.

Determining the Best Alloy for Specific Needs

Decision-Making Process Based on Hardness and Properties

Selecting the best aluminium alloy for a specific application requires considering the desired balance of hardness, strength, ductility, and other mechanical properties. This decision-making process involves:

1. Application Requirements: Understanding the specific demands of the application, such as load-bearing capacity, wear resistance, and environmental conditions.
2. Mechanical Properties: Evaluating the tensile strength, yield strength, and elongation of potential alloys to ensure they meet the performance criteria.
3. Heat Treatment Capabilities: Considering the feasibility and benefits of heat treatment processes to enhance hardness and other properties.
4. Cost and Availability: Balancing the material costs and availability with the required performance characteristics.

Case Studies or Examples of Comparisons

1. 6061 vs 7075 Aluminium:
   • 7075 Aluminium: Known for its superior hardness and strength, with a Brinell hardness of about HB 150 in the T6 temper. It is ideal for high-stress applications like aerospace and military components.
   • 6061 Aluminium: Offers moderate hardness (HB 90-95 in the T6 temper) and good machinability, making it suitable for automotive parts and construction.
2. 5052 vs 6063 Aluminium:
   • 5052 Aluminium: Provides good corrosion resistance and moderate hardness, commonly used in marine environments and for architectural applications.
   • 6063 Aluminium: A heat-treatable alloy that can achieve higher hardness through tempering, often used in extrusion processes for window frames and piping.
3. Reinforced Composites:
   • Adding zirconium diboride to aluminium matrices increases hardness and elastic modulus, making these composites suitable for applications requiring enhanced mechanical properties.

By understanding and comparing the hardness and mechanical properties of different aluminium alloys, engineers and manufacturers can make informed decisions to select the most appropriate materials for their specific needs, ensuring optimal performance and longevity in their applications.

Compliance and Standards

Importance of Standards in the Aluminium Industry

Compliance with industry standards is essential to ensure the reliability, safety, and performance of aluminium alloys across various applications. These standards provide a uniform framework for testing, classification, and quality assurance, ensuring that aluminium parts meet the stringent requirements of different industries such as aerospace, automotive, and construction.

Overview of Industry Standards

Several key standards govern the hardness and other properties of aluminium alloys, facilitating consistency and quality control across manufacturing and application processes.

AMS 2658D

The specification AMS 2658D, “Hardness and Conductivity Inspection of Wrought Aluminum Alloy Parts,” is crucial in the aerospace industry. It establishes the acceptance criteria for the hardness and electrical conductivity of finished or semi-finished parts of wrought aluminium alloys. This standard specifies the required values for hardness and conductivity, ensuring that the materials meet the necessary performance criteria for aerospace applications.

ASTM B647-10(2016)

The ASTM B647-10(2016) standard describes the use of the Webster hardness gage for measuring the hardness of aluminium alloys. Although less sensitive than Rockwell or Brinell hardness machines, the Webster gage is valuable for production control and field testing. This standard helps maintain quality during manufacturing and ensures that the aluminium parts adhere to specified hardness levels.

EN Standards

The EN standards provide a comprehensive framework for aluminium alloys, covering mechanical properties, heat treatment designations, and corrosion resistance. These standards, which have replaced older standards like BS1470, ensure consistency and quality across different applications and industries. They are essential for manufacturers to produce aluminium parts that meet the required specifications and performance criteria.

Specific Standards for Aluminium Hardness

Different aluminium alloys have specific standards and properties that must be met to ensure their suitability for intended applications. For instance:

• 2024-T351: Known for its high strength and fatigue resistance, this alloy is widely used in aerospace applications. The standards for 2024-T351 ensure that it meets the required hardness and mechanical properties for critical structural components.
• 6061-T651: This versatile alloy is used in various industries, including automotive and construction. Standards for 6061-T651 specify its hardness, tensile strength, and corrosion resistance, ensuring it performs reliably in diverse applications.
• 7075-T651: One of the highest-strength aluminium alloys, 7075-T651 is essential for high-stress applications such as aircraft wings and military vehicles. The standards for this alloy ensure it meets the stringent hardness and mechanical property requirements necessary for these demanding applications.

Ensuring Compliance in Manufacturing

Manufacturers must adhere to industry standards to ensure the quality and performance of aluminium alloys. This involves rigorous testing and certification processes to verify that the materials meet the specified criteria.

Testing and Certification Processes

• Hardness Testing: Methods such as Rockwell, Brinell, and Vickers hardness tests are employed to measure the hardness of aluminium alloys. These tests ensure that the materials meet the required hardness levels specified by industry standards.
• Conductivity Measurements: Electrical conductivity measurements, expressed as a percentage of the International Annealed Copper Standard (IACS), are used to verify the properties of heat-treated aluminium parts. These measurements are influenced by the amount of alloying elements in solid solution and the nature of the precipitates formed during heat treatment.

Consequences of Non-Compliance

Non-compliance with industry standards can have severe consequences, including:

• Product Failures: Aluminium parts that do not meet the required hardness and mechanical properties may fail under stress, leading to safety risks and potential catastrophic failures in critical applications such as aerospace and automotive components.
• Financial Losses: Non-compliance can result in costly recalls, repairs, and legal liabilities, affecting the manufacturer’s reputation and financial stability.
• Regulatory Penalties: Failure to adhere to industry standards can lead to regulatory penalties and loss of certifications, restricting the manufacturer’s ability to supply materials to certain industries.

Ensuring compliance with standards such as AMS 2658D, ASTM B647-10(2016), and the EN standards is essential for maintaining the quality, safety, and performance of aluminium alloys across various applications. These standards provide a framework for testing, classification, and application, helping manufacturers produce reliable and high-quality aluminium parts that meet the stringent requirements of different industries.

Which elements added to an aluminum alloy can most significantly enhance its hardness?

Elements such as magnesium, manganese, titanium, and rare earth elements (like lanthanum and yttrium) can be added to an aluminum alloy to enhance its hardness. Incorporating magnesium can notably increase the tensile strength of aluminum; for each 1% increase in magnesium, the tensile strength increases by approximately 34 MPa.

The introduction of manganese can supplement the strengthening effect and also decrease the susceptibility to thermal cracking.

Furthermore, the addition of rare earth elements (like lanthanum and yttrium) can enhance the resistance to the peeling of the oxidation layer. Hence, the incorporation of these elements can boost the hardness of aluminum alloys to varying degrees.

How can the hardness and wear resistance of aluminum alloys be improved through surface treatment methods?

There are several methods that can be employed to enhance the hardness and wear resistance of aluminum alloys through surface treatment:

Anodic oxidation treatment: This common method involves forming a dense oxide film on the surface of the aluminum alloy, thereby enhancing its hardness and corrosion resistance.

Surface electroplating: By coating a layer of metal (such as tin or copper) on the surface of the aluminum alloy, its hardness and wear resistance can be effectively improved.

Spraying wear-resistant coatings: A special wear-resistant coating is evenly sprayed on the surface of the aluminum alloy material to form a uniform, dense, and hard coating. This method not only improves wear resistance and corrosion resistance but also enhances the appearance.

Cold work hardening: This method hardens the aluminum alloy at room temperature through cold working, suitable for aluminum alloy materials that need to maintain their original shape.

Heat treatment: For certain specific types of aluminum alloys (like 6061), their strength and hardness can be enhanced through aging treatment. This usually involves an aging treatment after solution treatment.

Direct current magnetron sputtering deposition of amorphous CrAlN coating: This method deposits an amorphous CrAlN coating on the surface of the aluminum alloy, improving its corrosion resistance and wear resistance.

Thermal spraying and self-propagating high-temperature synthesis: These methods can prepare wear-resistant ceramic coatings on the surface of the aluminum alloy, significantly improving the wear resistance of the aluminum alloy.