How to Set the Hot Rolling Temperature for Aluminum Circles More Reasonably

The temperature setting for hot-rolling aluminum circles is a core process parameter that determines product microstructure, mechanical properties, surface quality, and production efficiency. A reasonable temperature regime must balance alloy characteristics, equipment capability, product specifications, and subsequent processing needs, precisely matching the range for “optimal plasticity, minimal deformation resistance, controlled microstructure, and fewest defects,” while avoiding issues like overheating, burning, work hardening, and abnormal grain growth. This article systematically explains the scientific methods and practical guidelines for setting the hot rolling temperature for aluminum circles, based on theoretical foundations, key temperature point settings, practical applications by alloy grade, process control, and optimization directions.

1. Core Theoretical Basis for Hot Rolling Temperature Setting

The selection of hot rolling temperature is not based on empirical values but on comprehensive decisions integrating materials science and practical process know-how. The core bases include:

1. Alloy Phase Diagram and Melting Point Constraints

   The melting point of pure aluminum is approximately 660°C; the solidus temperature of aluminum alloys decreases with alloying elements. Theoretically, the initial rolling temperature is set at 0.85–0.90 times the alloy solidus temperature, and the final rolling temperature at 0.65–0.70 times the solidus temperature. This range ensures maximum material plasticity, minimal deformation resistance, and prevents “burning” (liquefaction at grain boundaries, cracking, sharp strength drop) caused by melting of low-melting-point eutectic phases. For example, for 1050/1060 pure Al with a solidus ≈655°C, the theoretical initial rolling temperature is about 557–590°C, and the final rolling temperature is about 426–459°C.

2. Plasticity Diagram and Deformation Resistance Diagram

   Material plasticity and resistance differ significantly at various temperatures: too low a temperature intensifies work hardening, skyrockets rolling force, and easily causes edge cracking; too high a temperature leads to coarse grains, orange peel surface, and difficulty in subsequent cold rolling elimination. The temperature range featuring the peak plasticity and valley resistance​ must be chosen, balancing formability and energy consumption.

3. Recrystallization Behavior and Final Rolling Temperature

   The final rolling temperature directly determines the post-hot-rolling microstructure state: above the recrystallization stop temperature, a fine, uniform recrystallized structure can be obtained; below the recrystallization temperature, residual work hardening, uneven grains, and performance fluctuations occur; excessively high​ temperatures cause abnormal grain growth, reducing stamping and tensile properties. For alloys without phase transformation, the final rolling temperature should be 20–30°C above the recrystallization temperature to ensure complete recrystallization.

4. Process Chain Coordination Constraints

   Hot rolling temperature must align with subsequent cold rolling, annealing, and blanking needs: e.g., 5052 aluminum circles for cookware require a final rolling temperature that balances cold rolling reduction rates and the deep-drawing properties after final annealing; 8011 circles for battery foil require controlled grain size from hot rolling to ensure subsequent ultra-thin cold rolling and uniform strength.

2. Reasonable Setting of Key Temperature Points in the Complete Hot Rolling Process

Temperature control for hot-rolling aluminum circles spans the entire process: “Ingot Heating — Initial Rolling — Roughing — Finishing — Final Rolling — Coiling/Cooling.” Each stage requires precise matching and dynamic adjustment.

(I) Ingot Heating Temperature: The Foundation for Hot Rolling Temperature

Ingot heating is the critical pre-step for hot rolling, aiming to homogenize the structure, eliminate casting stress, and improve plasticity, while compensating for temperature drop from furnace exit to initial rolling.

• Heating Temperature Principle: 0.9Ts < Heating Temperature < 0.95Ts​ (Ts is the alloy’s actual solidus temperature), ensuring no burning and uniform structure.
• Reference Ranges by Alloy Grade:
  • 1xxx series pure Al (1050/1060/1100): 580–620°C, soak 4–8h (depending on ingot thickness)
  • 3xxx series (3003/3004): 560–600°C, soak 6–10h
  • 5xxx series (5052/5083): 540–580°C, soak 8–12h
  • 8xxx series (8011/8079): 570–610°C, soak 5–9h
• Practical Points: Heating requires “slow ramp-up — uniform soaking — short hold time” to avoid surface oxidation and grain coarsening; discharge temperature should be 10–20°C higher than the initial rolling temperature to compensate for transfer and radiation losses.

(II) Initial Rolling Temperature: Starting Point Control for Hot Rolling

The initial rolling temperature determines the deformation capability of the first pass and is crucial for preventing edge cracking and ensuring smooth rolling.

• Core Principle: Not lower than the alloy’s plasticity critical temperature, not higher than the burning temperature, balancing plasticity and microstructure.
• Initial Rolling Temperature Ranges by Alloy Grade (Industry Common Practice):

• Key Constraints: Too low initial temperature (e.g., 1060 <450°C) causes first-pass rolling force to exceed equipment limits, easily leading to edge cracks; too high (>540°C) results in coarse grains after roughing, difficult to refine in finishing.

(III) Roughing and Finishing Temperatures: Process Cooling and Deformation Matching

Hot rolling typically involves reversible roughing + continuous finishing. Temperature drops during the process due to deformation heat, radiation, and roll cooling. Dynamic control is needed via pass reduction rates, rolling speeds, and roll cooling intensity.

1. Roughing Temperature Control
   • Roughing involves high total reduction (typically 85%–95%), significant deformation heat partially compensates for temperature drop.
   • Roughing Exit Temperature: 1xxx: 420–460°C, 3xxx: 410–450°C, 5xxx: 400–440°C, ensuring sufficient plasticity for entry into finishing.
   • Pass Strategy: High reduction in initial passes (fast cooling), lower reduction + speed control in later passes to stabilize roughing exit temperature.
2. Finishing Temperature Control
   • Finishing Entry Temperature: 20–40°C lower than roughing exit temperature (e.g., 3003: 390–470°C? Note: This range seems high relative to roughing exit; likely 390-430°C is intended).
   • During Finishing: Control cooling rate (≤50°C/min) by adjusting rolling speed, inter-stand tension, and roll cooling water flow to avoid temperature plunge causing work hardening.
   • Core Objective: Ensure temperature throughout finishing ≥ recrystallization temperature, paving the way for achieving target final rolling structure.

(IV) Final Rolling Temperature: The Critical Endpoint Determining Product Properties

The final rolling temperature is the core of the hot rolling temperature regime, directly determining the grain size, mechanical properties, and suitability for subsequent processing of the aluminum circles.

• General Principle: 20–30°C above the alloy recrystallization temperature, ≥0.65 times solidus for non-phase-transformation alloys.
• Final Rolling Temperature Ranges by Alloy Grade (Industry Best Practice):

• Impact of Temperature Deviation:
  • Final temp too high (e.g., 1060 >380°C): Coarse grains (>50μm), orange peel/surface pitting after cold rolling, increased stamping crack risk.
  • Final temp too low (e.g., 5052 <280°C): Residual work hardening, uneven grains, strength fluctuations, rolling energy consumption ↑ by over 30%.

(V) Coiling/Cooling Temperature: Final Control for Microstructure Stability

Post-hot-rolling cooling rate and coiling temperature affect microstructure stability and internal stress.

• Cooling Method: Water mist cooling + air cooling, rate ≤50°C/min, avoiding rapid cooling causing internal stress and poor flatness.
• Coiling Temperature: 1xxx: 280–320°C, 3xxx: 270–310°C, 5xxx: 250–290°C, ensuring stable structure and no secondary recrystallization after coiling.

3. Customized Temperature Setting for Aluminum Circles in Different Applications

Aluminum circle applications vary widely; temperature must be precisely optimized based on product use, not just applying generic ranges.

1. Cookware/Pots & Pans Aluminum Circles (5052/3004)
   • Core Needs: High elongation, excellent deep-drawability, no orange peel.
   • Temperature Strategy: Initial rolling 480–510°C, final rolling 280–330°C (relatively low to control), suppress grain growth; roughing total reduction ≥93%, finishing with multiple low-reduction passes to refine grains.
2. Battery Foil/Packaging Foil Aluminum Circles (8011/1060)
   • Core Needs: Fine-grained structure, uniform strength, suitable for subsequent cold rolling to 0.006–0.02mm.
   • Temperature Strategy: Initial rolling 490–530°C (relatively high), final rolling 330–370°C (ensure recrystallization); roughing with fast, high reduction; finishing with controlled temperature and stable speed, ensuring grain size ≤20μm.
3. Lighting/Decorative Aluminum Circles (1050/1100)
   • Core Needs: Smooth surface, high flatness, easy anodizing.
   • Temperature Strategy: Initial rolling 480–510°C, final rolling 340–360°C; uniform temperature control throughout, avoid local overheating causing surface oxidation and color difference.
4. Automotive Parts/Structural Components Aluminum Circles (5083/6061)
   • Core Needs: High strength, matched plasticity, good weldability.
   • Temperature Strategy: Initial rolling 460–500°C, final rolling 300–340°C; roughing temperature control to prevent cracking, finishing ensures recrystallization, balancing strength and elongation.

4. Key Practical Control Points for Hot Rolling Temperature Setting

1. Accurate Temperature Measurement and Real-time Monitoring
   • Use infrared thermometers for multi-point measurement: ingot discharge, initial rolling, roughing exit, each finishing stand, final rolling exit, with error ≤±5°C.
   • Establish a temperature-rolling force-reduction rate linkage model to adjust rolling speed and roll cooling in real-time, compensating for temperature drop.
2. Temperature Drop Compensation and Process Matching
   • Winter/Low ambient temperature: Increase discharge temperature by 10–15°C, reduce transport loss; decrease roll cooling water by 10%–20%.
   • Thick gauge (>4mm): Use upper limit for initial rolling temp, lower limit for final rolling temp, ensuring uniform deformation; Thin gauge (<2mm): Use lower limit for initial rolling temp, upper limit for final rolling temp, avoiding coarse grains.
3. Alloy Composition Fine-Tuning and Temperature Adaptation
   • High-Mg (5xxx), High-Si (8xxx) alloys: Decrease initial rolling temp by 10–20°C, avoid low-melting-point phase precipitation; High-Mn (3xxx) alloys: Increase initial rolling temp by 5–10°C, improve plasticity.
4. Equipment Capability Matching
   • Reversing hot mill: Large inter-pass temperature drop requires higher discharge temperature and increased hold time; Continuous hot strip mill: Controllable temperature drop allows “lower initial, stable final” strategy, with lower energy consumption.

5. Common Temperature-Related Problems and Optimization Solutions

6. Summary: The Core Logic of Reasonable Temperature Setting

The essence of setting hot rolling temperature for aluminum circles is a systematic balance: “based on alloy characteristics, targeted at product properties, and executed through the process.”

1. Foundation in Theory: Use phase diagrams, plasticity diagrams, and recrystallization behavior to define temperature range boundaries, preventing burning and hardening.
2. Customization by Material: Differentiate initial and final rolling temperatures according to 1/3/5/8 series and application scenarios, matching performance requirements.
3. Process Precision: Multi-point temperature measurement and dynamic control throughout the process, compensating for cooling, stabilizing structure.
4. Coordinated Optimization: Link temperature with reduction rate, speed, and cooling, balancing quality, efficiency, and energy consumption.

In actual production, temperature parameters must be optimized through small trial rolls, considering equipment conditions, raw material composition, and product specifications, to establish a dedicated process curve. This is essential for stably producing hot-rolled aluminum circles with uniform structure, compliant properties, and excellent surface quality, laying a solid foundation for subsequent cold rolling, blanking, and deep processing.