【China Aluminum Industry Net】 I. INTRODUCTION Plating various metals onto the surface of aluminum and its alloys can significantly enhance their physical and chemical properties. When aluminum is used as a conductor, silver plating improves surface conductivity and electrical contact performance. To facilitate welding, copper, nickel, or tin plating is often applied. For improved wear resistance, thicker coatings are used. In terms of aesthetics, electroplated enamel is commonly employed. The electroplating of aluminum and its alloys has been explored for many years, but it still faces significant challenges. The presence of oxides between the metal and the coating, along with differences in thermal expansion coefficients, often leads to poor adhesion. Additionally, pinholes, residual plating solutions, and other factors contribute to peeling or delamination over time. As a result, the electroplating process for aluminum and its alloys remains in an exploratory phase, with no mature or universally effective method yet developed. This incompatibility continues to be a major obstacle in achieving high-quality plating and product pass rates. II. Traditional Electroplating Process for Aluminum and Its Alloys Although aluminum and its alloys can form coatings through electrolysis, the adhesion of these coatings is often weak and prone to peeling. A common approach involves first depositing zinc in an aqueous solution containing zinc oxide compounds before proceeding with electroplating—known as zinc displacement or deposition. Another method involves creating a thin porous oxide layer via anodizing, which then allows for better electroplating results. 2.1 General Plating Process for Aluminum and Its Alloys The general plating process for aluminum and its alloys consists of three main stages: pre-plating, electroplating, and post-plating. Pre-plating is a critical step that aims to remove oils, natural oxide layers, and other contaminants from the surface. A conventional process flow typically includes: degreasing, washing, deoxidation, rinsing, pickling, rinsing, activation, rinsing, primary zinc immersion, rinsing, zinc removal, secondary zinc immersion, rinsing, neutral nickel plating, rinsing, and subsequent plating. Some methods also use an anodized film instead of the zinc immersion process. 2.2 Limitations of the Traditional Pretreatment Process 1. The process is lengthy and involves numerous steps. 2. It is complex, with narrow operating ranges and strict control requirements. 3. The process is not widely applicable; different aluminum alloy grades require different pretreatment methods. 4. Despite careful control, the pass rate for decorative plating is only 85–90%, while functional plating achieves 60–70%. 5. Each solution has a short lifespan and limited processing time. Given these shortcomings, improvements are necessary. III. Improved General Pretreatment Process for Aluminum and Its Alloys Degreasing and caustic treatment in one – Washing – Pickling – Washing – Deashing – Washing – Alkaline Activation – Zinc Leaching – Washing – Neutral Nickel Plating – Washing – Subsequent Electroplating. IV. Practical Experience and Summary The new process addresses current defects in aluminum alloy plating by leveraging the unique properties of the material itself. Key improvements include: 1. A shorter process flow, which enhances adhesion by improving the purity of the aluminum surface. 2. Using alkaline activation instead of acid activation to effectively remove residual silicon and silica gel. 3. Eliminating direct washing after alkaline activation to prevent oxide formation during the second zinc immersion. 4. Simplified zinc immersion results in stronger bonding compared to traditional multi-step processes. 5. High versatility, suitable for all types of aluminum alloys. 6. A much higher pass rate, with some cases reaching nearly 100% when bond strength is good. 7. Simple and efficient operation in real production environments. 8. Proven stability in large-scale automated production lines. 9. Easy to improve upon the traditional process. 10. The use of Haocheng aluminum oxidation power supply enables faster film growth, reduces processing time, and saves resources, making the process more cost-effective.

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