Effect of Pretreatment Process on Microstructure and Adhesion of TC4 Alloy Electroplating Copper Coating
The copper sulfate cyanide-free technology was employed in the preparation of copper film on TC4 titanium alloy surface,the effects of pretreatment process(including activation and pre-coating) on coating microstructure, composition and film-substrate bonding force were studied; the coating forming process and fracture characteristic were analyzed; the film fracture mechanism was discussed. The results show that: activation promotes the formation of hydride conversion film, results in the closure effect and inhibits the permeation and diffusion of oxygen during coating forming process. The film shows a dense, uniform feature and the bonding force is significantly improved compared with the film without activation. Cu/Ni/Ti multilayer structure is formed after the activation pre-coating of Ni. Ti/Ni is easy to form a metallurgical bonding which will increase the stability of interface, then a better film-substrate strength is obtained. Analysis result shows that:after activation pre-coating treatment, fracture produces in the Cu/Ni interface, indicating that the bonding force between the coating film and substrate of the activated titanium is reliable.