3003 aluminum round sheet heat dissipation base: The influence of stress-relieving annealing parameters on thermal deformation

1. Introduction: Application Scenarios of 3003 Aluminum Disc Heat Sink Bases

3003 aluminum disc heat sink base is widely used in electronic devices (e.g., CPU heat sinks, LED drivers) and household appliances (e.g., refrigerator compressors).

Notably, it owes its popularity to moderate mechanical strength (140-160MPa tensile), excellent thermal conductivity (150-160W/(m·K)), and cost advantage (20%-25% lower than 6061 aluminum)—key attributes that make it a preferred choice for mid-power heat dissipation scenarios.

2. Thermal Deformation: A Critical Pain Point

However, the heat sink base requires strict flatness (≤0.05mm/100mm) and thermal stability for efficient heat transfer. Even minor deformation can disrupt heat conduction paths.

Processing (stamping, CNC milling) generates internal stress. When heated to 50-100℃ (typical electronic device operating temperature), this stress releases, causing warping or depression.

This deformation directly reduces contact area with heat-generating components by over 30% and increases thermal resistance by 50%-80%, severely impairing heat dissipation efficiency and shortening device lifespan.

3. Role of Mn Element in Internal Stress Distribution

Specifically, Mn in 3003 aluminum plays a dual role: it enhances corrosion resistance and mechanical strength but also alters internal stress behavior.

During processing, Mn reacts with Al to form Al₆Mn phases (0.5-1.0μm in size). These hard phases hinder dislocation movement, leading to stress accumulation at phase interfaces—with peak stress reaching 80-120MPa. This concentrated stress becomes a primary driver of thermal deformation.

4. Need for Optimized Stress Relief Annealing

Thus, stress relief annealing emerges as the key process to eliminate internal stress and inhibit thermal deformation.

Yet, improper parameter selection (e.g., overheating causing grain growth, rapid cooling generating new residual stress) can worsen deformation or reduce thermal conductivity—undermining the heat sink’s core function.

Thus, analyzing how annealing parameters (temperature, time, cooling rate) affect thermal deformation is essential to develop scientifically optimized processes.

5. Root Cause of Thermal Deformation: Processing-Induced Internal Stress

Fundamentally, processing generates two types of internal stress that collectively drive thermal deformation of the heat sink base:

(1) Macroscopic Internal Stress (Type I)

Stamping, the most common forming process for such discs, causes uneven plastic deformation: edge regions undergo 15%-20% deformation, while central regions only experience 5%-8%.

This uneven strain forms a “edge-tension, center-compression” stress field, with stress values reaching 60-90MPa. When heated, this stress relaxes, pulling edges upward and pushing the center downward—resulting in warping.

(2) Microscopic Internal Stress (Type II)

At the microscale, Al₆Mn phases block dislocation slip, leading to dislocation accumulation (dislocation density rises from an initial 1.0×10¹⁵ m⁻² to 2.5×10¹⁵ m⁻² after processing).

This accumulation creates local stress concentrations (peak stress 100-120MPa) at phase interfaces. When heated, these micro-stresses trigger grain rotation and boundary sliding, further exacerbating overall deformation.

6. Principle of Stress Relief Annealing

To address this issue, stress relief annealing eliminates internal stress via three sequential stages—all conducted below 3003 aluminum’s recrystallization temperature (300-350℃) to avoid grain growth and performance degradation:

(1) Atomic Diffusion Stage (250-300℃)

Heating energizes Al atoms, which diffuse along grain boundaries and dislocation lines.

This diffusion relieves stress concentrations at Al₆Mn phase interfaces, eliminating 30%-40% of microscopic internal stress without altering the alloy’s basic structure.

(2) Dislocation Movement Stage (300-320℃)

As temperature rises, dislocations gain sufficient energy to overcome Al₆Mn phase hindrance, enabling slip and climb.

Dislocation density drops below 1.2×10¹⁵ m⁻², eliminating 60%-70% of macroscopic internal stress. This stage is critical for reducing large-scale warping.

(3) Stress Relaxation Stage (Soaking)

Sustained soaking at the target temperature enables uniform stress release across the entire disc, avoiding local deformation caused by uneven stress relaxation.

The final stress elimination rate exceeds 80%, with grain size remaining stable at 5-8μm (initial size 4-6μm) and thermal conductivity loss limited to ≤5%—ensuring the heat sink’s performance is preserved.

7. Influence of Annealing Temperature on Thermal Deformation

Among all annealing parameters, temperature is the most critical for stress elimination. Its effects vary significantly across different ranges:

Specifically, the key conclusion is: temperature must stay within 300-320℃. This range ensures efficient stress relief while avoiding grain growth (which weakens mechanical strength) or Al₆Mn phase coarsening (which reduces thermal conductivity).

8. Influence of Soaking Time on Thermal Deformation

Beyond temperature, soaking time is equally important for ensuring uniform stress release. Its effects on the heat sink base are shown below:

Notably, 2-3h is the optimal soaking time. Short soaking causes uneven stress relief (edge-center difference >15%), leading to asymmetric warping; long soaking, while improving uniformity, increases surface oxide film thickness (which raises thermal resistance) and reduces production efficiency.

9. Influence of Cooling Rate on Thermal Deformation

Additionally, cooling rate controls the generation of new thermal stress during the final stage of annealing:

Practically, a 3-5℃/min medium cooling rate balances deformation control and production efficiency for most commercial heat sink bases. Rapid cooling generates new stress, while slow cooling is only feasible for high-precision, low-volume applications due to its long cycle time.

10. Experimental Verification: Scheme Design

To quantitatively validate the above conclusions, experiments were conducted using 3003 aluminum discs (100mm diameter, 5mm thickness) with an initial internal stress of 70-90MPa (simulating post-stamping conditions).

An L9(3³) orthogonal experiment was designed to isolate the effects of the three core parameters:

• Temperature: 280℃ (low), 310℃ (optimal), 340℃ (high)

• Time: 1h (short), 2.5h (optimal), 4h (long)

• Cooling rate: 2℃/min (slow), 4℃/min (medium), 8℃/min (rapid)

Test indicators included thermal deformation (ΔL), stress relief rate (η), thermal conductivity (λ), and flatness—all aligned with industrial quality standards.

11. Experimental Results: Parameter Significance

Analysis of the experimental data revealed that parameter influence followed the ranking: T (R=0.18) > t (R=0.07) > v (R=0.05).

This confirms that temperature has the most significant impact on thermal deformation, consistent with the theoretical analysis above. Key experimental results are highlighted below:

12. Optimal Parameter Combination

Based on these results, Experiment No. 5 (T=310℃, t=2.5h, v=2℃/min) was identified as the optimal parameter combination:

• ΔL=0.04mm (well below the industrial threshold of ≤0.1mm)

• η=85% (residual stress reduced to 10-12MPa)

• λ=156W/(m·K) (excellent thermal conductivity retained)

• Microstructure stability: grain size 6-7μm, Al₆Mn phase size 0.6-0.8μm (no coarsening or growth)

13. Verification Experiment Results

To confirm the stability of the optimal process, 100 samples were processed using the identified parameters:

• Average ΔL=0.038mm (standard deviation 0.005mm), achieving a 100% qualification rate

• Average stress relief rate=84.5%, average thermal conductivity=155.2W/(m·K)

• Process stability met mass production requirements, with no significant performance fluctuations between batches.

14. Engineering Application: Specification Adaptation

In practical engineering applications, different heat sink base specifications (thickness, diameter) require tailored annealing parameters—due to variations in internal stress distribution and heat transfer efficiency:

Thicker discs, for example, require slightly higher temperatures and longer soaking times to ensure stress is fully released from their central regions.

15. Quality Control Measures

To ensure consistent performance in mass production, a full-process quality control system is required:

(1) Incoming Inspection

• Initial internal stress of 3003 aluminum discs must be ≤100MPa (pre-annealing is required if exceeding this value)

• Grain size must be 4-6μm, and Al₆Mn phase volume fraction 0.3%-0.5% (verified via SEM)

(2) Annealing Monitoring

• Furnace temperature uniformity must be ≤±5℃ (monitored in real time using a multi-point thermometer) to avoid local overheating

• Nitrogen atmosphere purity ≥99.99% to prevent surface oxidation (oxide film thickness ≤0.8μm)

(3) Finished Product Test

• ΔL ≤0.1mm (tested using a laser flatness meter with ±0.001mm accuracy)

• Residual stress ≤20MPa (sampled and tested via X-ray stress analyzer per GB/T 7704-2019)

• Thermal conductivity ≥145W/(m·K) (sampled and tested via laser flash method per GB/T 22588-2008)

16. Cost-Efficiency Balance

While optimizing performance is critical, cost and production efficiency must also be considered in industrial settings:

• For mass production: Use a continuous annealing furnace operating at the optimal parameters (310℃×2.5h, 4℃/min cooling). This configuration achieves a capacity of ≥500 pieces per batch and unit energy consumption ≤0.5kW·h/kg—balancing performance and cost.

• For abnormal handling: Over-deformed samples (ΔL=0.12-0.15mm) can undergo secondary annealing (300℃×1.5h, 3℃/min cooling). This process reduces ΔL to below 0.08mm, with rework cost ≤15% of the original production cost—minimizing waste.

17. Conclusions: Key Findings

In summary, this study yields three core conclusions regarding 3003 aluminum disc heat sink bases:

(1) Optimal Parameter Range

The optimal stress relief annealing parameters are 300-320℃ temperature, 2-3h soaking time, and 3-5℃/min cooling rate. Within this range:

• Internal stress relief rate ≥80%

• Thermal deformation ΔL ≤0.08mm

• Thermal conductivity retention ≥95%

(2) Core Mechanism

Al₆Mn phases must be controlled at 0.6-0.8μm to avoid excessive stress concentration. Annealing parameters must match the diffusion characteristics of Al₆Mn to prevent phase coarsening or grain growth—both of which degrade performance.

(3) Engineering Value

Applying these optimal parameters reduces the heat sink base’s thermal resistance by 40%-50% and improves heat dissipation efficiency by 25%-30%—effectively addressing the thermal deformation pain point in mid-power electronic devices.

18. Future Research Directions

Looking ahead, two directions will further advance the performance of 3003 aluminum disc heat sink bases:

(1) Low-Temperature Rapid Annealing

Add trace Zr (0.05%-0.1%) to 3003 aluminum to refine grains. This modification lowers the recrystallization temperature to 280℃, enabling rapid annealing within 1.5h—improving production efficiency by 40% while maintaining deformation control.

(2) Intelligent Temperature Control

Combine AI algorithms with real-time ultrasonic stress detection to automatically optimize annealing parameters. This system will adjust temperature, time, and cooling rate dynamically based on the initial stress of incoming discs, achieving precise thermal deformation control (ΔL ≤0.05mm) for high-end applications.

This study provides a quantitative, actionable guide for the heat treatment process of 3003 aluminum disc heat sink bases. By solving thermal deformation-induced heat dissipation failure, it promotes the wider application of this cost-effective material in high-power electronics and new energy fields.