Electrolytic metal coating, also known as electroplating, is a fundamental process in the metallurgical industry for enhancing the surface properties of metal components. Zamak, a zinc alloy containing approximately 4% aluminium with traces of copper and magnesium, greatly benefits from this treatment both functionally and aesthetically.
Principles of Electrolysis and Electroplating
Electrolysis is an electrochemical phenomenon in which electrical energy drives chemical reactions in an electrolyte. There are different types of electrolysis, each with specific objectives. Metallic electroplating, used for coating zamak, involves the controlled transfer of metal ions from the electrolyte to a conductive substrate, forming a uniform and adherent layer.
In contrast, electrolytic dissolution or anodization generates protective oxides or modifies the surface without depositing metal. Chemical decomposition electrolysis is used to extract elements or gases from compounds and does not directly apply to metallic coatings. Therefore, electroplating is the appropriate technique for depositing copper, nickel, or chrome on zamak, providing corrosion resistance, surface hardness, and decorative finish.
Surface Preparation of Zamak
The success of electroplating largely depends on substrate preparation. Before coating, zamak parts undergo a rigorous cleaning and activation process. Oils, greases, and particles are initially removed through chemical degreasing or ultrasonic cleaning, ensuring the surface is entirely free of contaminants.
Next, a controlled acid pickling is performed using diluted hydrochloric or sulfuric solutions to remove surface oxides and adjust relative roughness, promoting adhesion of the metallic layer. In many cases, a thin initial layer of copper or nickel, known as a “strike layer,” is applied to ensure uniform adhesion of the final coating. Finally, a passivation treatment may be performed to stabilise the surface and eliminate any remaining contaminants, optimising nucleation of metal ions during electroplating.
Types of Coatings on Zamak
Coatings on zamak can serve decorative, protective, or functional purposes depending on the application. Decorative chrome plating provides a shiny finish with excellent wear resistance, while functional nickel plating increases hardness and corrosion resistance. The latter is often part of multilayer systems that include copper, nickel, and sometimes chrome.
For components exposed to friction or mechanical wear, hard chrome or electropolishing is used, combining high hardness with low surface roughness. Selective coatings are also possible through masking, leaving conductive or assembly areas free without compromising the uniformity of the rest of the coating.
Process Variables in Electroplating
Controlling operational variables is essential to achieve a uniform and durable coating. Current density directly affects deposition rate and the microstructure of the layer; excessively high densities can cause roughness or surface defects, while low densities unnecessarily prolong the process.
Electrolytic bath temperature determines ion mobility and metal solubility. For nickel and copper electroplating on zamak, it is typically maintained between 45 and 55 °C. The chemical composition of the electrolyte, combined with specific additives, regulates levelling and uniformity of the metal layer. Finally, bath agitation ensures homogeneous ion distribution and thickness, which is especially critical for parts with complex geometries or intricate details.
Quality Control
Inspection of coated parts ensures compliance with the most stringent industrial standards. Coating thickness is verified using layer micrometres or X-ray fluorescence, while adhesion is tested through controlled scratch or pull-off tests.
Corrosion resistance is evaluated with accelerated tests, such as salt spray, and microscopic examination detects microdefects or inclusions. These controls ensure that the coated surface possesses the durability and functionality required for both industrial and decorative applications.
Jegan: Expertise and Commitment
At Jegan, we have over five decades of experience in casting and surface treatment. Our treatment facility in Eibar has become a benchmark for innovative anti-corrosion solutions for zamak. We not only manufacture high-quality components but also ensure their durability and resistance through our specialised processes.
The combination of expertise, technology, and commitment to excellence allows us to offer tailored solutions that enhance our clients’ performance, ensuring that zamak parts are the best choice for overcoming corrosion challenges.
