Impact of Reduction Rate Miscontrol on Grain Non-Uniformity and Heat Dissipation Defects in 6.35μm Aluminum Foil for VR/AR Micro Heat Sinks

1. Introduction: Application Characteristics of Aluminum Foil for Micro Heat Sinks in VR/AR Devices and the Significance of Reduction Rate Control

Aluminum foil for micro heat sinks in VR/AR devices (primarily 1235/8079 alloys, 6.35μm thick) serves as a core heat dissipation component in VR/AR headsets, controllers, and similar devices. Due to the limited internal space of such devices (e.g., heat dissipation cavity volume ≤15cm³ in VR headsets), heat sinks must be miniaturized (size 3-15mm) with uniform thermal conductivity to avoid local overheating—especially since chip heat power ranges from 5-15W, requiring a local temperature difference ≤3℃.

During the rolling process, the reduction rate (total reduction rate = [(initial thickness – final thickness)/initial thickness]×100%; single-pass reduction rate = [(initial thickness of the pass – final thickness of the pass)/initial thickness of the pass]×100%) is a key parameter regulating grain evolution. According to 2024 VR/AR industry data, 42% of device heat dissipation failures stem from “local overheating of micro heat sinks,” which can be traced to improper reduction rate control of aluminyo foil for micro heat sinks in VR/AR devices: ① Insufficient total reduction rate causes uneven grain size, leading to a 7W/(m·K) difference in local thermal conductivity of the heat sink; ② Excessive fluctuation in single-pass reduction rate creates a “fine-grain/coarse-grain” gradient, forming heat dissipation dead zones (temperature difference >5℃); ③ Uneven transverse reduction rate results in edge overheating, reducing the service life of VR/AR device chips by 20%.

To address these challenges, it is first necessary to clarify the relationship between reduction rate, grain structure, and thermal conductivity—laying a theoretical foundation for precise rolling of this type of aluminum foil.

2. Theoretical Relationship Between Reduction Rate, Grain Structure, and Thermal Conductivity for Aluminum Foil in VR/AR Micro Heat Sinks

(1) Core Mechanism of Grain Regulation by Reduction Rate: Adapting to Miniature Heat Dissipation Requirements

The rolling of aluminum foil for micro heat sinks in VR/AR devices involves “multi-pass cold rolling” (8-12 passes, reducing thickness from 2mm to 6.35μm, with a total reduction rate ≈99.68%). The reduction rate influences dynamic recrystallization (DRX) through “deformation stored energy,” which in turn determines grain suitability for heat dissipation:

1. Deformation Stored Energy and Recrystallization: The critical stored energy for DRX of this aluminum foil (1235 haluang metal) is 75J/m³. A single-pass reduction rate of 20%-25% generates stored energy of 80-110J/m³, forming equiaxed grains of 5-7μm—ideal for ensuring uniform thermal conductivity in micro heat sinks;

2. Grain Orientation and Thermal Conductivity: A reasonable reduction rate (22%-24% per pass) promotes the {111} texture to account for >60% (thermal kondaktibiti 12% higher than random texture). In contrast, abnormal reduction rates (>30%) increase the {100} texture proportion to 18%, reducing thermal conductivity by 5%—failing to meet the heat dissipation precision requirements of VR/AR devices.

(2) Quantitative Model of Grain Structure and Thermal Conductivity: Addressing the Specificity of Micro Heat Sinks

Due to the small size and high heat flux density (10-20W/cm²) of VR/AR micro heat sinks, a more precise grain-thermal conductivity relationship is required. Derived from metal thermal conduction theory, the formula is:

λ = λ₀ × [1 – k×(6/d)]

• λ₀: Thermal conductivity of single-crystal aluminum (237W/(m·K) at 25℃);

• k: Grain boundary scattering coefficient (0.12 for this type of aluminum foil);

• d: Grain size (M; micro heat sinks require d=5-7μm with a standard deviation ≤2μm).

When d increases from 5μm to 15μm, λ rises from 225W/(m·K) to 232W/(m·K), a difference of 7W/(m·K). For micro heat sinks, this difference causes a local temperature difference exceeding 4℃—far beyond the ≤3℃ limit for VR/AR devices—resulting in heat dissipation dead zones.

3. Three Scenarios of Uneven Grain Structure Caused by Improper Reduction Rate Control (Adapted to VR/AR Heat Dissipation Needs)

To quantify the impact of improper reduction rate control on grain uniformity and heat dissipation, Table 1 summarizes the key parameters of each failure scenario, directly linking process defects to device performance issues:

Table 1: Grain Structure and Heat Dissipation Parameters Under Improper Reduction Rate Scenarios

(1) Insufficient Total Reduction Rate (<50% in Critical Passes): Inadequate Recrystallization and Local Overheating of Heat Sinks

1. Process Characteristics: For aluminum foil for micro heat sinks in VR/AR devices, the total reduction rate in the 3 passes before finish rolling (thickness from 50μm→25μm→12μm) must be ≥50%. If reduced to 40% (50μm→30μm), the stored energy drops to 65J/m³—below the critical value for DRX;

2. Impact on Grain Structure and Heat Dissipation: As shown in Table 1, this scenario forms a bimodal grain distribution. The corresponding λ difference in the micro heat sink reaches 8W/(m·K), leading to a 10℃ local temperature difference in VR/AR headset chips and causing frame drops—directly affecting user experience.

(2) Excessive Fluctuation in Single-Pass Reduction Rate (Deviation >8%): Grain Gradient and Heat Dissipation Dead Zones

1. Process Characteristics: The single-pass reduction rate in the 2 passes before final rolling (25μm→12μm→6.35μm) must be stable at 45%-50%. Roller wear may cause fluctuations to 38%-48% (10% deviation);

2. Impact on Grain Structure and Heat Dissipation: Notably, this fluctuation creates alternating “cold/hot strips” along the rolling direction. As Table 1 indicates, the thermal conductivity difference reaches 8W/(m·K), and the temperature difference exceeds 10℃—far beyond the VR/AR device limit—forming irreversible heat dissipation dead zones.

(3) Uneven Transverse Reduction Rate (Edge-Center Deviation >5%): Edge Overheating and Reduced Device Reliability

1. Process Characteristics: Abnormal roller crown (0.02mm→0.04mm) causes a 6% transverse reduction rate deviation (48% at the center, 42% at the edges);

2. Impact on Grain Structure and Heat Dissipation: Beyond the above scenarios, transverse unevenness primarily affects device durability. Table 1 shows the edge temperature is 7℃ higher than the center, accelerating sealing rubber aging and increasing the failure rate from 1.5% to 4.8%—a major cost driver for manufacturers.

4. Verification of VR/AR Device Heat Dissipation Failures Caused by Uneven Grain Structure

Building on the scenario analysis, both laboratory testing and industrial case studies were conducted to validate the practical impact of grain unevenness. Table 2 presents detailed laboratory verification data, while real-world cases further confirm the findings.

Table 2: Laboratory Verification Results of Micro Heat Sink Performance

(1) Laboratory Verification (Matching Micro Heat Sink Scenarios)

1. Sample Preparation: Select aluminum foil for micro heat sinks in VR/AR devices with “fluctuating single-pass reduction rates” (fine-grain zone d=5μm, coarse-grain zone d=14μm) and fabricate 10mm×5mm×6.35μm micro heat sinks;

2. Testing: As Table 2 shows, applying a heat flux of 15W/cm² (simulating VR chip heat generation) revealed a 11℃ temperature difference—far exceeding the ≤3℃ requirement. Laser flash analysis (NETZSCH LFA 467) confirmed the thermal conductivity difference of 8W/(m·K);

3. Pangwakas na Salita: Heat dissipation dead zones caused by uneven grain structure push VR device chip temperatures above the threshold (60℃), triggering frequency reduction protection.

(2) Industrial Case: Failure Analysis of a VR Device Manufacturer

Sa 2023, a VR headset manufacturer used aluminum foil for micro heat sinks in VR/AR devices with “uneven transverse reduction rates,” leading to:

• As reflected in Table 2, the edge temperature of the heat sink reached 58℃ (mga bes. 51℃ at the center), causing frequent chip frequency reduction (frame rate dropping from 90Hz to 75Hz);

• The customer complaint rate rising from 2.3% sa 8.5%, with a single after-sales cost exceeding 5 million yuan;

• After replacing the foil with optimized reduction rates (as shown in the third row of Table 2), the heat dissipation temperature difference dropped to 2.5℃, and the complaint rate fell back to 1.2%.

5. Precision Reduction Rate Control Strategies for Aluminum Foil in VR/AR Micro Heat Sinks

Based on the verification results, targeted control strategies were developed to address each failure scenario. The core lies in staged reduction rate design, stable single-pass control, and uniform transverse distribution—with key parameters detailed in Table 3.

Table 3: Staged Reduction Rate Design for 6.35μm 1235 Aluminum Foil (Initial Thickness 2mm)

(1) Staged Total Reduction Rate Design: Adapting to Grain Requirements for Micro Heat Dissipation

As Table 3 illustrates, the finish rolling stage (passes 7-8) is critical—maintaining a total reduction rate ≥50% ensures deformation stored energy reaches 90-110J/m³. This triggers sufficient DRX, resulting in grain sizes of 5-7μm with a standard deviation ≤2μm—perfectly matching the thermal conductivity needs of VR/AR micro heat sinks.

(2) Stable Single-Pass Reduction Rate Control: Suppressing VR/AR Heat Dissipation Dead Zones

1. Roller Monitoring: Use a laser profilometer for real-time wear detection (accuracy 0.001mm). Automatically replace rollers when wear exceeds 0.02mm, reducing fluctuations from ±8% to ±3%—a key step to avoid the “fine-grain/coarse-grain” gradient in Table 1;

2. Tension Coordination: Maintain stable finish rolling tension at 15-18kN (fluctuation ≤±1kN). Compensate for deviations by adjusting rolling speed (100-120m/min), limiting single-pass fluctuations to ≤5%;

3. Online Feedback: Use an X-ray thickness gauge (accuracy 0.1μm) to collect data every 10ms. Adjust the pressure of the reduction cylinder (accuracy 0.01MPa) when thickness deviation exceeds 0.3μm—ensuring consistency with the single-pass rates in Table 3.

(3) Uniform Transverse Reduction Rate: Avoiding Edge Overheating

1. CVC Roller Crown: Adjust the crown to 0.015-0.02mm based on heat sink width (3-15mm), limiting transverse pressure deviation to ≤3%—addressing the edge-center issue in Table 1;

2. Edge Heating: Install an edge heating device (50-60℃) at the rolling mill inlet to reduce edge deformation resistance, lowering edge-center deviation from >5% to ≤3%;

3. Grain Monitoring: Integrate an online EBSD system to collect grain data from 3 transverse sections per meter of foil. Adjust roller crown when grain size difference exceeds 15%—ensuring the transverse uniformity reflected in the optimized sample of Table 2.

6. Conclusions and Outlook

Improper reduction rate control of aluminum foil for micro heat sinks in VR/AR devices triggers a chain reaction of “stored energy→grain structure→thermal conductivity,” forming heat dissipation dead zones (maximum temperature difference 11℃) and compromising device stability. As demonstrated by Tables 1-3, implementing “total finish rolling reduction rate ≥50%, single-pass fluctuation ≤±5%, transverse deviation ≤3%” achieves grain sizes of 5-7μm (standard deviation ≤2μm) and thermal conductivity differences ≤3W/(m·K)—meeting the ≤3℃ heat dissipation requirement for VR/AR devices.

Future development directions focus on two areas: ① Develop an “AI reduction rate prediction system” to address the trend of higher VR/AR device power densities (chip power reaching 20W by 2025), enabling proactive deviation correction; ② Integrate pulse current-assisted rolling to further reduce grain size differences, advancing this type of aluminum foil toward “zero heat dissipation dead zones.”

Core Principle: Reduction rate control for aluminum foil for micro heat sinks in VR/AR devices must prioritize “grain uniformity adapted to miniature heat dissipation.” Only when parameters are precisely matched to the heat dissipation needs of the device— as reflected in the data from Tables 1-3—can long-term reliable operation of VR/AR equipment be guaranteed.