Aluminum casting & mold design services

Introduction

In Japanese manufacturing, enhancing product functionality and reducing weight are urgent challenges, leading to a rapid increase in the adoption of aluminum alloys as a solution. Particularly in fields requiring high reliability and performance, such as automotive, aerospace, and industrial machinery components, the demand for aluminum castings, die casting, sand casting, permanent mold casting, etc., has grown year by year, with domestic production reaching approximately 2 million tons in 2022, Source: Japan Aluminum Association,. Essential for meeting these demands for high functionality is the ’heat treatment’ of aluminum alloys.

Heat treatment is a technology that dramatically improves the mechanical properties of aluminum alloys, such as strength, ductility, corrosion resistance, and dimensional stability, making it an extremely critical process that dictates the performance of the final product. However, the choice and management of heat treatment are complex, and thorough quality control is indispensable, especially in overseas procurement. Inappropriate heat treatment can lead to premature product failure and performance degradation, potentially causing significant impacts across the entire supply chain.

This article focuses on the primary heat treatments for aluminum alloys—T4, T6, and T7—detailing their effects on strength and ductility, their mechanisms, and a comparison based on specific numerical data. Our aim is to provide insights for Japanese manufacturing executives, procurement managers, and purchasing managers to choose optimal aluminum alloy products and mitigate quality risks in overseas procurement. We will also touch upon the heat treatment technology and quality control system offered by Daiwa Aluminum Vietnam, introducing its value as a reliable overseas procurement partner.

What is Aluminum Alloy Heat Treatment: Basics of T4, T6, and T7 Treatments

Heat treatment of aluminum alloys primarily consists of two processes: ’Solution Treatment’ and ’Aging Treatment.’ By combining these processes, the microstructure of the alloy is altered to achieve desired mechanical properties.

Solution Treatment

Solution treatment involves heating the alloy to a high temperature to uniformly dissolve solute elements, such as magnesium, silicon, and copper, responsible for age hardening into the aluminum matrix. For A356 material, a common aluminum casting alloy, it is typically held at temperatures ranging from approximately 495°C to 540°C for several hours, Source: Japan Aluminum Association,. After the solute elements are dissolved at this temperature, rapid cooling, quenching, forms an unstable state called a supersaturated solid solution. If this rapid cooling rate is insufficient, solute elements will precipitate, significantly reducing the effectiveness of subsequent age hardening.

Aging Treatment

Aging treatment is a phenomenon where, from the supersaturated solid solution formed after solution treatment, solute elements precipitate as fine particles, hindering the movement of dislocations in the crystal and thereby improving hardness and strength. There are two types of aging treatment: natural aging and artificial aging.

• Natural Aging: This is a phenomenon where hardening gradually progresses by holding the material at room temperature for an extended period. The size of the precipitates is very small, and ductility is relatively maintained.
• Artificial Aging: This treatment involves holding the material at a relatively high temperature, e.g., 150°C to 200°C, for several hours to tens of hours to accelerate the formation of precipitates, achieving high hardness and strength in a shorter time. Properties can be adjusted by controlling the size and distribution of precipitates.

T4 Treatment, Solution Treatment + Natural Aging,

T4 treatment involves rapid cooling after solution treatment, followed by natural aging at room temperature. This treatment is chosen when high ductility and toughness are desired while ensuring a certain level of strength. Natural aging progresses over several days to weeks until the final properties are achieved. For example, A356 material subjected to T4 treatment typically achieves a tensile strength of approximately 230-250 MPa and an elongation of about 8-12%, Source: ASM Handbook Volume 15: Casting,. It is suitable for parts requiring impact absorption and machinability.

T6 Treatment, Solution Treatment + Artificial Aging,

T6 treatment involves rapid cooling after solution treatment, followed by artificial aging at high temperatures. This treatment aims to maximize the strength and hardness of aluminum alloys. The temperature and time for artificial aging are strictly controlled depending on the alloy type and desired properties. For example, for A356 material, it is common to hold it at 155°C for approximately 4 to 6 hours. T6 treatment increases the tensile strength of A356 material to approximately 290-320 MPa and yield strength to about 210-240 MPa, a significant improvement compared to T4 treatment. However, ductility tends to decrease to about 3-6%, Source: JIS H 5202:2010,. It is widely applied to structural components and engine parts subjected to high loads.

T7 Treatment, Solution Treatment + Over-aging,

T7 treatment involves rapid cooling after solution treatment, followed by ’over-aging’ at a higher temperature or for a longer duration than T6 treatment. The primary purpose of this treatment is to improve resistance to stress corrosion cracking, SCC, at a slight expense of strength. In over-aging, precipitates coarsen, and stress concentration is alleviated, thereby reducing SCC susceptibility. For A356 material, T7 treatment results in a tensile strength of approximately 270-300 MPa and a yield strength of about 190-220 MPa, which is slightly lower than T6 treatment, but elongation is maintained at about 4-7%, while SCC resistance is significantly improved. It is applied to components used in high-temperature environments or corrosive atmospheres, such as aircraft parts. For instance, reports indicate that while T6-treated alloys may fracture in approximately 100 hours in stress corrosion cracking tests, T7-treated alloys can withstand over 5000 hours, Source: Heat Treatment and Mechanical Properties of Aluminum Alloy Castings,.

The application examples and properties of each treatment are summarized as follows:

• T4 Treatment: High ductility, moderate strength. Impact-absorbing parts, complex-shaped parts.
• T6 Treatment: High strength, moderate ductility. Structural components, engine blocks, wheels.
• T7 Treatment: High stress corrosion cracking resistance, moderate strength and ductility. Aircraft parts, parts in corrosive environments.

Impact of T4, T6, and T7 Treatments on Strength and Ductility: A Comparison with Specific Numerical Values

Heat treatment of aluminum alloys results in distinct differences in their mechanical properties. Here, using the widely used A356 aluminum alloy as an example, we will compare the effects of T4, T6, and T7 treatments on tensile strength, yield strength, and elongation using specific numerical data, and examine their trade-off relationships in detail.

From the table above, the impact of each heat treatment on mechanical properties is clearly understood.

• • T4 Treatment, Solution Treatment + Natural Aging,:

A356-T4 material exhibits a tensile strength of 230-250 MPa and a yield strength of 110-130 MPa, showing a significant increase in strength compared to F material, as-cast,. Most notably, the elongation is very high at 8-12%. This is because fine precipitates are uniformly dispersed, hindering dislocation movement while allowing for significant plastic deformation. It is suitable for parts that may be subjected to impact or require deformation absorption after welding.

• • T6 Treatment, Solution Treatment + Artificial Aging,:

A356-T6 material exhibits even higher strength than T4 treatment, with a tensile strength of 290-320 MPa and a yield strength of 210-240 MPa. This is because artificial aging forms precipitates of optimal size and density, most effectively inhibiting dislocation movement. However, in exchange for this high strength, elongation decreases to about 3-6%. This is due to the increased density of precipitates, which tends to make the material more brittle. It is ideal for applications requiring high strength and rigidity, such as automotive suspension components and engine brackets.

• • T7 Treatment, Solution Treatment + Over-aging,:

A356-T7 material has a tensile strength of 270-300 MPa and a yield strength of 190-220 MPa, which is slightly lower than T6 treatment but still higher than F or T4 materials. Elongation is around 4-7%, slightly higher than T6 material. The greatest advantage of T7 treatment is a significant improvement in resistance to stress corrosion cracking, SCC,. Over-aging causes precipitates to coarsen, alleviating stress concentration at grain boundaries, thereby reducing the risk of SCC. It is chosen for applications requiring long-term reliability in harsh environments, such as aircraft components and parts used in marine environments. For example, for aircraft parts, it has been reported that while T6-treated alloys fracture in approximately 100 hours in stress corrosion cracking tests, T7-treated alloys can withstand over 5000 hours, Source: Heat Treatment and Mechanical Properties of Aluminum Alloy Castings,.

These numerical data highlight the importance of clearly prioritizing properties such as strength, ductility, and corrosion resistance in product design and choosing the optimal heat treatment. For instance, T6 treatment is often chosen for automotive wheels due to high strength and lightweighting, but T4 treatment may be considered for chassis components requiring impact absorption. Furthermore, for applications demanding extremely high reliability, such as aircraft parts, improving SCC resistance through T7 treatment may be prioritized.

Microstructural changes also significantly contribute to these property differences. Rapid cooling after solution treatment results in a uniform distribution of solute atoms as a supersaturated solid solution. In T4 treatment’s natural aging, very fine precipitate precursors called GP zones, Guinier-Preston Zone, slowly form at room temperature. In T6 treatment’s artificial aging, GP zones grow, and more stable metastable phases, e.g., Mg2Si phase, precipitate at optimal size and density, strongly hindering dislocation movement. In T7 treatment’s over-aging, this metastable phase further grows and coarsens, transforming into a stable phase. The coarsening of precipitates weakens their effect on hindering dislocation movement while changing the precipitation morphology at grain boundaries, thereby improving SCC resistance, Source: Japan Institute of Light Metals,.

Heat Treatment Technology and Quality Control Provided by Daiwa Aluminum Vietnam

For Japanese manufacturers considering overseas procurement, one of the biggest concerns is often ’consistency of quality.’ Especially in the heat treatment process, which significantly affects product performance, a robust quality control system is extremely important. Daiwa Aluminum Vietnam, with its many years of experience in aluminum casting manufacturing, state-of-the-art equipment, and stringent quality control system, provides heat treatment services that meet the diverse needs of its customers.

Overview and Capacity of Heat Treatment Facilities

Daiwa Aluminum Vietnam has introduced multiple state-of-the-art heat treatment furnaces, capable of flexibly handling various heat treatments such as T4, T6, and T7. Our heat treatment furnaces excel in temperature uniformity, achieving precise temperature control within ±5°C. This ensures uniform mechanical properties throughout the product and minimizes quality variations. For example, the cooling rate after solution treatment is maximized for rapid quenching effect and ensures the formation of a supersaturated solid solution through optimized water bath temperature control and transfer speed. Our annual production capacity reaches 15,000 tons, aluminum castings, allowing for flexible response to customer production plans, from mass production to high-mix, low-volume production.

Track Record and Expertise in Each Heat Treatment, T4, T6, T7,

We have accumulated a track record of T4, T6, and T7 treatments in a wide range of fields, including automotive parts, motorcycle parts, and industrial machinery components. Specifically, we propose and implement optimal heat treatments according to the customer’s product application and required properties, such as T6 treatment for automotive engine brackets and suspension components requiring high strength and lightweighting, and T7 treatment for marine-related parts where corrosion resistance and reliability are paramount.

The expertise accumulated over many years allows us not only to apply standard heat treatment conditions but also to make fine adjustments according to individual alloy compositions, casting conditions, and product shapes. For example, for complex-shaped castings, jig design and optimization of the cooling process are essential to minimize deformation due to thermal stress, and we possess the technical capabilities to address such challenges.

Quality Assurance System: ISO Certification, Inspection System

Daiwa Aluminum Vietnam has obtained ISO 9001 certification, an international quality management system standard, and has established a strict quality control system for all manufacturing processes, including the heat treatment process. The main elements of our quality assurance system are as follows:

• Process Control: We monitor and record temperature profiles, time, and cooling conditions of heat treatment furnaces in real-time to ensure traceability. We can provide data proving that the heat treatment conditions were appropriate for each batch.
• Inspection System: We conduct various mechanical property tests in-house on heat-treated products, including hardness tests, Brinell hardness, Rockwell hardness, tensile tests, tensile strength, yield strength, elongation, and microstructure observation, microscopic examination of grain size, precipitate confirmation,. This confirms that the heat treatment imparts the designed properties. We perform approximately 15,000 hardness tests and 5,000 tensile tests annually.
• Dimensional Inspection: To strictly manage dimensional changes due to heat treatment, we also conduct precise dimensional inspections using 3D measuring machines. Deformation after heat treatment is typically kept below 0.1%.
• Regular Equipment Calibration and Maintenance: Heat treatment furnaces and inspection equipment are regularly calibrated and maintained to consistently ensure high accuracy and reliability.

Contribution to Reducing Quality Risks in Overseas Procurement

When procuring aluminum castings from overseas, customers’ biggest concerns are often quality variations, delivery delays, and communication issues. Daiwa Aluminum Vietnam contributes to addressing these challenges in the following ways:

• Consistent Quality: We provide products of stable quality through a strict quality control system and skilled technicians. We have established a management system compliant with Japanese quality standards, reliably meeting customer specifications.
• Transparent Information Provision: We provide detailed reports on heat treatment data and inspection results, striving to ensure customers can use our products with confidence.
• Technical Support: We respond to technical consultations regarding heat treatment from the product design stage and collaboratively explore optimal solutions. Our technicians are capable of smooth communication in Japanese.
• Consideration for Cost and Delivery Time: Through competitive production costs in Vietnam and efficient supply chain management, we contribute to customer cost reduction and on-time delivery. The average lead time, including casting, heat treatment, and inspection, is approximately 4 weeks.

Daiwa Aluminum Vietnam is committed to providing value not just as a manufacturing partner, but as a reliable quality assurance partner in your supply chain.

Conclusion

This article has detailed the importance of aluminum alloy heat treatment on product performance, specifically the mechanisms and properties of T4, T6, and T7 treatments. Heat treatment of aluminum alloys is an indispensable technology not only for increasing strength but also for optimizing the balance with other critical mechanical properties such as ductility and corrosion resistance.

• T4 treatment is suitable for parts requiring high ductility, ideal for applications demanding impact absorption and machinability.
• T6 treatment is designed to maximize strength and hardness and is widely applied to structural components subjected to high loads.
• T7 treatment, while sacrificing some strength, significantly improves stress corrosion cracking resistance, making it essential for parts requiring long-term reliability in harsh environments.

The choice of these heat treatments dictates the final performance and reliability of the product, requiring careful consideration from the design stage. Particularly in overseas procurement of aluminum castings, quality control of the heat treatment process is extremely important for mitigating risks across the entire supply chain.

Daiwa Aluminum Vietnam provides high-quality aluminum casting products that meet diverse customer needs through state-of-the-art heat treatment facilities, a stringent quality control system backed by ISO 9001 certification, and technical expertise cultivated over many years of experience. We support various heat treatments, including T4, T6, and T7, and guarantee product quality through thorough inspections such as hardness tests, tensile tests, and microstructure observations. For Japanese manufacturing executives, procurement managers, and purchasing managers, Daiwa Aluminum Vietnam promises to be an ideal overseas procurement partner that balances cost competitiveness with quality reliability. We invite you to consider our technical capabilities and services.