The Difference Between Electrophoretic Black and Blackening

Blackening and electrophoretic black are two commonly used surface blackening processes for metal workpieces, but there are many differences between the two.

Electrophoretic Blackening

Electrophoretic blackening is an electrostatic deposition technique. In this process, metal parts are immersed in an electrophoresis tank, where a constant voltage is applied to cause the positively charged black pigment molecules in the electrophoretic solution to migrate from the cathode to the anode. Through an oxidation reaction, a dense, uniform black oxide film is formed on the metal surface, which bonds firmly to the metal substrate. This treatment protects the metal surface from natural oxidation and corrosion, enhances the hardness and wear resistance of metal parts, and improves the surface’s aesthetic appeal.

Blackening

Blackening refers to the natural oxidation of metal materials when exposed to air, water, or external chemical agents, resulting in the formation of a black oxide layer. The primary compounds in this layer are manganese dioxide and phosphates. This oxide layer has relatively low adhesion and is prone to flaking. Furthermore, it lacks the uniformity and density of the oxide film produced by electrophoretic blackening, which may lead to color variations on the surface and affect its aesthetic appeal.

• Corrosion and Rust Resistance
• The blackened oxide film contains microscopic pores, resulting in relatively weak rust resistance. It must be sealed with oil to enhance its protective effect. Conventional salt spray testing yields results of only 1–4 hours, making it suitable only for indoor, dry, and non-corrosive environments with light-duty conditions. Electrophoretic black resin coatings create a sealed barrier that completely blocks moisture, air, and acid/alkali corrosion. They achieve salt spray resistance of over 300 hours, offering long-lasting rust protection and exceptional weather resistance, making them suitable for humid, outdoor, and corrosive environments.

• Electrical Conductivity and High-Temperature Resistance
• The blackened coating exhibits good electrical conductivity, does not affect the workpiece’s grounding or anti-static functions, and offers excellent high-temperature resistance, withstanding short-term exposure to temperatures up to 300°C. It is suitable for high-temperature operations and workpieces requiring electrical conductivity and grounding. Electrophoretic black coating is an organic resin insulating layer that completely blocks the workpiece’s conductivity; it cannot be used on conductive or grounded components. Furthermore, its maximum temperature resistance is only 200°C, and in high-temperature environments, the coating is prone to aging, cracking, and peeling.

Blackening surface treatment is primarily used for decorative purposes and is suitable for metal crafts, watches, and utensils; electrophoretic coatings, on the other hand, are more suitable for industrial applications, such as the automotive, electrical, and construction industries.

Jiaxing Aoke specializes in blackening and electrophoretic blackening metal surface treatment services. With our proven processes, we can tailor blackening solutions to meet the specific applications, usage scenarios, and precision requirements of your workpieces. Welcome your orders!