Study On The Adhesion Strength Of Electroless Deposited Nickel Alloy Coatings

In this paper, the electroless nickel plating on the surface of ABS by electroless plating was introduced, and the effect of surface state on adhesion strength were studied. Followed on copper substrate by electroless plating, the effect of plating process on deposition rate, internal stress and coating adhesion were studied. The effect of heat treatment temperature on the plating structure, the micro hardness, coating internal stress and adhesion were investigated. The substrate and coating properties were analyzed by scanning electron microscopy(SEM), roughness meter, digital micro hardness tester, X-ray diffraction(XRD), universal testing machine and other modern texting means. Concrete research content and the experimental results are as follows:a)The influences of the coarsening time on matrix morphology, roughness and the influences of coarsening and activating on coating adhesion on ABS matrix were studied. The results showed that micro-pores appeared on the substrate for 200mL/L sulfuric and chromic acid aqueous solution of 400g/L coarsening processing. With coarsening time was prolonged, micro-pores became bigger,when extend to 40 minutes, some parts will appear lager pits. Surface roughness of substrate showed a rising tendency, surface generated new groups, coarsening time from 20 min to 30 min was advisable. The proportion of coarsening time prolonged, coating adhesion increased for activating of 15 min. The proportion of activating prolonged, coating adhesion was increased first and then remained stable.b)Ni-Zn-P alloy coatings were prepared by electroless plating on pure copper. the effect of the content of nickel sulfate main salt, sodium hypophosphite reduction agent,bath temperature and pH on deposition rate, internal stress and coating adhesion were studied. The results showed that with the higher the concentration of nickel sulfate, deposition rate showed a rising tendency. When the concentration of sodium hypophosphite was less than 25g/L, with increased of concentration, deposition rate increased. The deposition rate was increased with increased of the temperature. The higher of pH value, the higher of deposition rate was. When the concentration of nickel sulfate was less than 25g/L, with increased of concentration, coating internal stress increased, when the concentration of nickel sulfate was greater than 25g/L, with increased of concentration, coating internal stress decreased sharply. With the concentration of sodium hypophosphite increased, coating internal stress first and then decreased. Coating internal stress was increased with increased of the temperature. With the higher of pH value, coating internal stress increased. With the higher the concentration of nickel sulfate, coating adhesion decreased, when the concentration of nickel sulfate increased to 25g/L, coating adhesion forced to 12.44 MPa. When the concentration of sodium hypophosphite was less than 20g/L, coating adhesion remained at around 12.44 MPa, When the concentration of sodium hypophosphite was greater than 20g/L, coating adhesion showed a rising tendency. As temperature rise, Ni-Zn-P alloy coating adhesion showed a rising tendency. When pH value was less than 10, with the higher of pH value, coating adhesion keep on the same level, When pH value was greater than 10,coating adhesion reduced.c)The effect of heat treatment temperature on the plating structure, the micro hardness, coating internal stress and adhesion were investigated. The results showed that plated consist of amorphous phase and nickel solid solution, with the increase of temperature, the hardness increased. Heat treatment from 100℃ to 300℃ was beneficial to reduce internal stress in plating. Internal stress depend on the length of heat treatment time. After heat treatment at 300 ℃ for 1 hour, internal stress decreased to 111.36 MPa, after heat treatment at 300 ℃ for 4 hour, internal stress decreased to 70.38 MPa; Heated 1 hour with furnace cooling to room temperature, with the increase of temperature, coating adhesion increased gradually. Heated 4 hour with furnace cooling to room temperature, with the increase of temperature, coating adhesion increased first and then decreased.