Composite Aluminum Discs for Kitchenware: Rolling Process Design and Performance Verification to Eliminate Interlayer Bubbles and Delamination

1. Introduction

Composite aluminum discs for kitchenware are core substrates for high-end cookware (e.g., non-stick frying pans, stainless steel-lined soup pots, and induction-compatible woks), requiring three non-negotiable core performances to meet daily cooking demands:

1. Thermal conductivity uniformity: Temperature deviation across the disc surface must be ≤5% to avoid local overheating (e.g., burnt egg edges in a frying pan) — this is achieved via the outer 3003 alloy, which has a thermal conductivity of 200W/(m·K), 30% higher than pure aluminum;

2. Structural strength: Yield strength ≥180MPa to resist deformation during stamping (e.g., forming a 10cm-deep soup pot) and long-term use — the middle 5052 alloy (Al-Mg 系) provides this strength, with Mg content of 2.5% enhancing corrosion resistance (critical for acidic foods like tomatoes);

3. Thermal shock resistance: No cracking after 20+ cycles between -20℃ (refrigerated storage) and 260℃ (oven baking) — a key requirement for cookware that transitions between cold storage and stovetop heating.

The typical composite structure is 3003/5052/3003, with diameters ranging from 100mm (small saucepans) to 300mm (large woks) and total thicknesses of 3-8mm (thicker for soup pots, thinner for frying pans).

A critical quality bottleneck is interlayer defects: Bubbles with diameter ≥0.5mm cause uneven heating (temperature differences up to 50℃), while delamination leads to cookware deformation or even detachment of the non-stick coating. According to 2024 data from the China Kitchenware Association, 32% of composite aluminum disc scrap stems from interlayer issues, with an average single-batch loss of ≥800,000 yuan (e.g., a 5,000-piece batch of 24cm pan discs  due to bubbles).

Traditional rolling processes fail to address these defects due to mismatched parameters (e.g., insufficient temperature for atomic diffusion, uneven pressure leaving air pockets). Thus, precise synergistic control of rolling temperature, pressure, and reduction rate is essential to achieve “zero interlayer bubbles and delamination”.

2. Causes of Interlayer Defects

Interlayer defects arise from the combined effects of material inherent properties and process fluctuations, with clear mechanisms for each:

(1) Material-Related Barriers

The 3003 and 5052 alloys in composite discs have inherent property differences that hinder interface bonding, as detailed in the table below:

(2) Process-Related Defects

Even with well-matched materials, improper rolling parameters directly generate defects:

• Temperature mismatch:

• • Below 380℃: Atomic kinetic energy is too low — Mg atoms in 5052 can only diffuse 0.1-0.2μm, failing to cross the oxide layer. This leaves “physical contact gaps” (5-10μm) between layers, which trap air and form bubbles.

• • Above 500℃: Mn in 3003 precipitates as Al₆Mn hard particles (1-3μm), which scratch the 5052 layer during rolling. high temperature accelerates oxidation, thickening the Al₂O₃ layer to >10nm, worsening bonding.

• Pressure issues:

• • Below 10MPa: Insufficient force to expel interlayer air (initial thickness 5-10μm). The compressed air forms bubbles (0.3-1mm diameter), and the interface contact area is only 60-70%, leading to weak bonding.

• • Pressure deviation >5MPa: Due to uneven roll stress, the disc edge (high pressure) overflows metal, while the center (low pressure) retains air — a common defect in large-diameter discs (≥250mm).

• Unreasonable reduction rate:

• • Total reduction rate <40%: Metal deformation is insufficient to flatten interface irregularities (3-5μm), leaving micro-bubbles that expand during cookware heating.

• • Single-pass reduction rate >30%: Metal flows too fast (>100mm/s), entraining air into the interface. Excessive deformation stress also creates “shear cracks” (1-2μm) between layers, which develop into delamination after cooling.

3. Synergistic Regulation Strategy

To address the above causes, a synergistic strategy is developed for 3003/5052/3003 composite discs (taking φ200mm, target thickness 6mm as an example), focusing on “temperature as the foundation, pressure as the key, and reduction rate as the guarantee”.

(3.1) Material Properties for Reference

Understanding layer-specific functions and requirements guides parameter design:

(3.2) Core Rolling Parameters (3003/5052/3003, φ200mm, Target Thickness 6mm)

Parameters are divided into three stages to match the bonding process:

(3.3) Single-Pass Reduction Rate Allocation

A 5-pass rolling schedule balances deformation and bonding, avoiding excessive stress:

(3.4) Traditional vs. Optimized Processes

The optimized process addresses key flaws in traditional methods, with measurable defect reductions:

4. Auxiliary Process Optimization

Core parameters alone are insufficient — auxiliary processes eliminate hidden defects and stabilize quality:

5. Performance Verification

To validate the optimized process, comprehensive testing was conducted on 3003/5052/3003 composite discs (φ200mm, thickness 6mm) by a national-level aluminum processing laboratory:

(5.1) Interlayer Quality Test

Tests followed GB/T 3880.3-2022 (aluminum composite foil standards), with results below:

(5.2) Kitchenware Performance Test

Discs were formed into 24cm non-stick frying pans and 20cm soup pots for practical performance testing:

• Thermal conductivity uniformity:

• • Test conditions: Induction cooker (2000W), heating to 200℃, 5 test points (center + 4 edges, 50mm apart).

• • Results: Temperature difference reduced from 45℃ (traditional) to 12℃ (optimized) — meets the “no local burnt” requirement for frying pans.

• Thermal shock resistance:

• • Test conditions: 20 cycles of -20℃ (freezer, 2h) → 260℃ (oven, 30min), rapid transfer (≤30s).

• • Results: Optimized discs showed no delamination or cracking; traditional discs delaminated at the 8th cycle (edge separation ≥2mm).

• Formability:

• • Test conditions: Stamping into 10cm-deep soup pots (pressure 0.5MPa, temperature 180℃).

• • Results: Forming qualification rate increased from 78% (traditional, defects: cracking, delamination) to 99% (optimized, no defects).

6. Industry Application Case

A leading Chinese kitchenware enterprise (annual output: 10 million sets, main products: non-stick pans) faced severe quality issues in 2023:

• Problem: 8.5% of frying pans were recalled due to interlayer bubbles (customer complaints: “food burns on one side”); a single batch of 5,000 φ24cm discs was scrapped, causing a 2-day production line shutdown and 1.2 million yuan in losses.

• Optimization Measures: Adopted the synergistic strategy above, including:

1. 1. Adjusting preheating temperature from 390℃ to 430℃, extending holding time to 35min;

1. 2. Installing a zoned hydraulic system (edge pressure +4MPa) to solve center bubbles;

1. 3. Implementing 1200-grit polishing and low-temperature annealing (290℃, 2.5h);

1. 4. Using CrN-coated rolls (Ra 0.08μm) to reduce indentation defects.

• Results:

• • Bubble rate of composite discs: 6.8% → 0.05%;

• • Peel strength: 11.8MPa → 20.3MPa;

• • Customer complaints: 8.5% → <0.3%;

• • Annual loss reduction: 8 million yuan;

• • Thermal conductivity of pans: Increased by 15% (faster heating, energy saving ~10%).

7. Conclusions & Outlook

(1) Core Conclusions

The key to achieving “zero interlayer bubbles and delamination” for composite aluminum discs for kitchenware lies in synergistic control of three core parameters (temperature, pressure, reduction rate) plus auxiliary processes:

• Temperature: 420-450℃ preheating + 400-430℃ rough rolling + 380-400℃ finish rolling — ensures sufficient atomic diffusion while avoiding oxidation and precipitation;

• Pressure: 15-20MPa zoned pressure (edge +3-5MPa) — completely expels interlayer air and ensures uniform contact;

• Reduction rate: 50%-60% total rate + 16.7%-30% single-pass gradient allocation — balances deformation and stress;

• Auxiliary processes: Degreasing + polishing + inert gas protection + annealing — eliminates hidden defects and stabilizes bonding.

This combination achieves bonding strength ≥18MPa, bubble rate ≤0.1%, and meets all kitchenware performance requirements.

(2) Future Development Directions

1. Intelligent parameter regulation:

• • Develop a BP neural network model that inputs real-time data (temperature, pressure, roll speed) and outputs defect probability. When the probability exceeds 5%, the system automatically adjusts parameters (e.g., increases induction heating power if temperature drops, or adjusts hydraulic pressure if bubbles are detected via ultrasonic sensors). This will reduce reliance on manual operation and improve process stability to >99%.

2. New composite structures:

• • For heavy-duty cookware (e.g., outdoor camping pots), develop 3003/6061/3003 composite discs (middle layer 6061 alloy: yield strength ≥270MPa). Tailored parameters: preheating temperature 450-480℃ (matches 6061’s recrystallization temperature), rolling pressure 20-25MPa (compensates for higher strength), and single-pass reduction rate ≤25% (avoids cracking).

3. Eco-friendly processes:

• • Replace traditional alkaline degreasing with ultrasonic water-based degreasing (reduces chemical usage by 50%) and develop recyclable rolling oil (recycling rate ≥80%) to meet global environmental standards (e.g., EU REACH).

The optimization of composite aluminum disc rolling processes not only improves kitchenware quality and reduces costs but also provides a technical reference for other composite metal materials (e.g., aluminum-copper, aluminum-steel), driving innovation in the lightweight metal processing industry.