Analysis of AC Power Supply System in Aluminum Electrolytic Coloring Process

September 22, 2025 185 Views

I. Definition of AC Power Supply System in Aluminum Electrolytic Coloring Process

The AC Power Supply System in Aluminum Electrolytic Coloring Process specifically refers to a specialized power supply equipment and its accompanying control system that provides precise and controllable alternating current (typically sine wave or square wave) for the coloring process of anodized films (porous aluminum oxide) on aluminum and its alloys.

Its core working principle is: In a coloring bath containing metal salts, aluminum parts that have undergone anodic oxidation treatment are used as electrodes, and alternating current is applied. During the negative half-cycle of the AC, metal ions (such as tin, nickel, cobalt, copper, etc.) are reduced and deposited at the bottom of the micropores in the oxide film; during the positive half-cycle, some of the deposited metal may be slightly redissolved. Through this repeated "deposition - dissolution" dynamic process, metal particles are precisely deposited in the micropores. Due to the light interference effect, metal particles at different depths scatter different colors, achieving rich coloring.

In addition to the power supply main unit capable of outputting AC, this "system" typically integrates voltage/current control units, time controllers, soft-start units, process monitoring and protection units, etc.

II. Applications and Performance Requirements

1. Main Applications

  • Coloring: Core function, providing various durable colors such as bronze, black, champagne, red, gold, etc. on aluminum surfaces.
  • Color Adjustment: Precisely controlling electrical parameters (voltage, time, waveform) to fine-tune color depth, achieving color consistency and reproducibility.
  • Sealing Promotion: Some AC coloring processes (especially tin salt coloring) promote the subsequent sealing process.

2. Key Performance Requirements

  • Pure and Stable Output Waveform: Requires low distortion sine wave or regular square wave. Waveform distortion introduces harmonics, leading to uneven coloring, mottling, or color deviation.
  • Precisely Adjustable Output Voltage/Current: Coloring voltage is usually low (5-25V AC), but requires high adjustment accuracy (typically ±0.1V) and good stability (fluctuation < 1%), as voltage directly determines color depth.
  • Adjustable Frequency and Control: Output AC frequency is usually 50/60Hz. Advanced power supplies allow frequency adjustment in the 20-100Hz range. Frequency affects metal ion penetration and deposition speed, subtly influencing coloring efficiency and color.
  • Stable Output Capability: When the load (aluminum part area) changes, the power supply must maintain the set voltage or current constant to ensure consistent color for the entire batch of products.
  • Soft Start Function: Voltage should smoothly rise from 0V to the set value at startup to prevent current impact causing uneven coloring or damage to the oxide film.
  • Automatic Commutation Function: For square wave power supplies, the positive and negative half-cycle switching time (duty cycle) must be accurate and adjustable to ensure the balance of deposition and dissolution processes.
  • Good Protection Functions: Must have overcurrent, overvoltage, short circuit, overheating and other protections to prevent product scrap and equipment damage.

III. Process Overview (How AC Power Supply Participates in the Process)

The general process flow for aluminum electrolytic coloring is: Aluminum material → Pretreatment (degreasing, alkaline etching, chemical polishing, etc.) → Anodic oxidation (forming porous oxide film in DC sulfuric acid bath) → Electrolytic coloring → Sealing → Finished product

The electrolytic coloring step is where the AC power supply system comes into play. The specific process is as follows:

  1. Immerse the anodized aluminum parts into a coloring bath containing metal salts (such as stannous sulfate, nickel sulfate, etc.).
  2. Suspend counter electrodes (usually carbon rods or stainless steel plates) in the bath solution.
  3. Connect the two output terminals of the AC power supply to the aluminum parts and counter electrodes respectively (AC has no strict cathode/anode distinction, positive and negative polarities constantly alternate).
  4. Set the required parameters such as voltage, time, frequency, etc., and start the power supply.
  5. Under the action of AC, metal ions are reduced and deposited at the bottom of the micropores in the oxide film.
  6. After reaching the set time, the power supply automatically turns off. Remove the aluminum parts for washing and sealing treatment.

IV. Differences from Electroplating Rectifiers

Although both aluminum electrolytic coloring AC power supplies and electroplating DC rectifiers are power supplies for electrochemical processing, they have fundamental differences. The specific differences are shown in the following table:

Characteristic Aluminum Electrolytic Coloring AC Power Supply Electroplating DC Rectifier
Output Current Type Alternating Current (AC), sine wave or square wave. Direct Current (DC), usually pure DC or smooth DC with very low ripple coefficient.
Core Working Principle Utilizes the alternating characteristic of AC. Metal ions are reduced during the negative half-cycle, with slight dissolution during the positive half-cycle, achieving deposition - dissolution balance of metal particles in micropores. Utilizes the unidirectional conductivity of DC to continuously reduce metal ions into metal atoms, forming a dense metal coating on the workpiece (cathode) surface.
Process Purpose Coloring. The deposited metal particles do not form a continuous coating, only used to produce color. The film's corrosion and wear resistance come from the previous anodic oxidation film. Electroplating. Forms a continuous, dense functional metal coating on the substrate surface (such as anti-corrosion, wear resistance, decoration, conductivity, etc.).
Electrical Connection Method Power supply terminals have no positive/negative distinction, alternately connected to workpiece and auxiliary electrode. Power supply has clear positive (+) and negative (-) poles. Positive connected to anode (usually soluble metal), negative connected to cathode (workpiece).
Waveform Requirements High requirements. Waveform purity directly affects coloring uniformity and color. Relatively lower requirements, but requires stable output, small ripple coefficient (<5%) to obtain uniform coating.
Output Voltage Low, usually between 5-25V AC. Wide range, from low voltage plating types (e.g., gold plating, 3-6V DC) to high voltage plating types (e.g., chrome plating, 12-18V DC).
Output Current Relatively small, depends on coloring area and current density. Can be very large, from hundreds of amperes to tens of thousands of amperes, depending on plating tank size and productivity.
Key Control Parameters Mainly voltage control (voltage stabilization mode), time, frequency, waveform. Mainly current control (constant current mode), current density (A/dm²) is the core process parameter. Time, temperature.

Summary

In short, the aluminum electrolytic coloring AC power supply is a precision device that provides special electrical energy (pure, controllable AC) for a special chemical process (depositing metal particles in oxide film micropores). The electroplating rectifier is a high-power device that provides stable DC for the traditional electrodeposition process (forming metal coatings on workpiece surfaces). The two have completely different design intentions, working principles and application fields, and cannot be used interchangeably.