5052 อลูมิเนียมวงกลมรีดร้อน: วิธีล็อคอินอย่างแม่นยำ “หน้าต่างอุณหภูมิสีทอง”?

In the field of aluminum processing, 5052 อลูมิเนียมอัลลอยด์, with its excellent corrosion resistance, ความแข็งแรงปานกลาง, และขึ้นรูปได้ดี, is a popular base material for products like can ends, ชิ้นส่วนยานยนต์, and electronic housings. อย่างไรก็ตาม, the quality of a hot-rolled aluminum circle, transitioning from an ingot to a sheet with uniform structure and qualified properties, is largely determined during the hot rolling process. Among the factors, precise control of the hot rolling temperature window​ is the core process lifeline connecting the as-cast structure to the desired final properties.

This article will systematically analyze the determination logic, practical operating ranges, and control points for the two key thresholds in the hot rolling of 5052 วงกลมอลูมิเนียม: ที่ start-rolling temperature​ และ finish-rolling temperature, providing you with a clear operational guide.

1. Understanding the Basics: Why is the Temperature Window So Critical?

5052 belongs to the Al-Mg series of non-heat-treatable strengthening alloys. Its properties are primarily achieved through solid solution strengthening and subsequent work hardening. The core purpose of hot rolling is not just “การเสียรูป” แต่ “recreation”:

1. Breaking down the as-cast structure: Eliminating coarse dendrites and composition segregation.
2. Inducing complete recrystallization: Obtaining uniform, fine equiaxed grains through hot deformation and dynamic recrystallization.
3. Laying the foundation for subsequent processing: Providing a坯料 (billet) with good plasticity and a uniform structure, facilitating later cold rolling with high reduction rates or deep drawing.

Determining the temperature window is precisely about finding the optimal balance between “preventing overheating” และ “promoting recrystallization,” and between “reducing deformation resistance” และ “avoiding grain coarsening.”

2. Starting Point Control: How to Determine the Start-Rolling Temperature?

The start-rolling temperature is the temperature of the ingot after homogenization treatment as it enters the first rolling pass. It determines whether hot rolling can commence smoothly and the quality of the initial structure.

Core Basis for Determination:

• Phase Diagram Constraints: The solidus line of 5052 is approximately 607°C. It must be kept well below this temperature to prevent overheating. It also needs to avoid the melting range of low-melting-point eutectic phases (เช่น, Al₃Mg₂).
• Homogenization Requirement: The ingot must first be fully homogenized at 500–540°C to dissolve soluble phases and achieve compositional uniformity. The start-rolling temperature should connect with this, ensuring the homogenization effect is not lost due to cooling.

Pre-Treatment: Homogenization Process Parameters

Homogenization is an indispensable pre-treatment process before hot rolling. Its parameters directly affect the feasibility of starting rolling and the quality of the initial structure.

โต๊ะ 1: Reference Homogenization Process Parameters for 5052 Aluminum Alloy Ingot

Recommended Window and Practical Points:

• ช่วงอุณหภูมิ: 500–540°C. โดยปกติ, 510–530°C​ is preferred.
• Scenario Refinement:
  • Thin-gauge products (≤3mm): Can use the lower limit (~500°C), conducive to obtaining finer grains for subsequent precision machining.
  • Thick-gauge products (>3มม): Can use the medium-to-upper limit (520–540°C), utilizing higher plasticity to reduce deformation resistance in the initial passes.
• Key Control:
  1. Heating must be uniform; the cross-section temperature difference of the ingot should be ≤ ±5°C.
  2. Prioritize the use of non-contact pyrometers (เช่น, infrared) for real-time surface temperature monitoring, replacing contact thermocouples which have greater lag.

3. End Point Control: How to Determine the Finish-Rolling Temperature?

The finish-rolling temperature is the temperature of the material at the end of hot rolling. It directly determines the microstructure and initial properties of the output product and is the top priority​ of temperature window control.

Core Basis for Determination:

• Recrystallization Law: Must be above the alloy’s complete recrystallization temperature (~330°C for 5052) to ensure the deformed structure is replaced by new, strain-free equiaxed grains.
• Grain Size Constraint: Excessively high temperature (>380องศาเซลเซียส) leads to abnormal grain growth (coarsening) after recrystallization, impairing mechanical properties and surface quality.

Recommended Window and Scenario Application:

• General Safe Window: 330–350°C. ภายในช่วงนี้, a balance between complete recrystallization and appropriate grain size can usually be achieved.

Key Control:

1. Dynamic Adjustment: Precisely control the finish-rolling temperature by adjusting rolling speed and emulsion cooling intensity. Speed increase of ~10% leads to a temperature rise of ~5-10°C.
2. Precise Monitoring: At the exit of the final pass, a high-response pyrometer must be used for monitoring, with deviation controlled within ±5°C.

4. Full-Process Temperature Control Practice Map

Knowing the start and end temperatures is not enough; temperature fluctuations throughout the entire process must be “tracked in real-time and managed dynamically.” The diagram below reveals the typical temperature evolution path and key control nodes during hot rolling:

Interpretation of Core Control Points:

1. Roughing Stage: Temperature naturally drops from the starting point. อย่างไรก็ตาม, through methods like roll preheating, it should be ensured that when rolled to an intermediate thickness (เช่น, 20มม), the temperature is not lower than 400°C to prevent a sharp increase in deformation resistance.
2. Finishing Stage: The material temperature is precisely controlled into the target finish-rolling temperature window through the “on-off” and flow regulation of the emulsion spray. This is a core function of modern rolling mill automatic control systems.
3. Exception Handling: As shown in the chart, once the temperature deviates from the window, there must be clear corrective measures. Too low requires furnace “วิธีการรักษา,” too high requires emergency cooling to prevent batch structural defects.

5. Equipment and Verification: Support for Window Implementation

• Equipment Support: Modern hot rolling lines should be equipped with multi-point, non-contact infrared temperature measurement systems, linked in a closed loop with mill speed and cooling systems for control. Rolls need internal cooling channels to prevent local heating of the stock due to the rolls themselves overheating.
• Performance Verification: Hot-rolled coils produced within the correct temperature window (เช่น, start 520°C, finish 340°C) should have a uniform, โครงสร้างเกรนที่ตกผลึกใหม่เท่ากัน. After subsequent cold rolling and annealing (O-อารมณ์), typical mechanical properties should stably reach: แรงดึง (฿) ≥175 MPa, ความแข็งแรงของผลผลิต (0.2 รูเปียห์) ≥65 MPa, การยืดตัว (ก) ≥32%. This is the ultimate benchmark for testing whether the temperature window is reasonable.

6. บทสรุป

Determining the hot rolling temperature window for 5052 aluminum circles is essentially a precise process design following materials science principles:

• Start-rolling temperature (510–530°C)​ is the starting point for safety and plasticity, needing to carry forward the homogenization effect.
• Finish-rolling temperature (330–350°C)​ is the endpoint for structure and properties, and must ensure complete recrystallization.

นี้ “golden window” is not a fixed value and requires fine-tuning based on the product’s end use, specification thickness, and equipment capability. The key to success lies in transforming the temperature “setpoint” into a “stable measured value” on the production line, which relies on accurate detection, rapid response, and closed-loop automatic control. Only in this way can the excellent inherent qualities of 5052 aluminum alloy be perfectly activated and passed on through the hot rolling process.