Abnormal concentration of main salt (e.g. nickel sulfate is too high/too low), insufficient buffer (boric acid), and excessive chloride will lead to coarse crystallization or uneven deposition of plating layer, which will trigger surface roughness.
Author: Anna
I. Defects caused by plating solution factors
Disorder of plating solution composition
Abnormal concentration of main salt (e.g. nickel sulfate is too high/too low), insufficient buffer (boric acid), and excessive chloride will lead to coarse crystallization or uneven deposition of plating layer, which will trigger surface roughness.
Countermeasures: Regularly test and adjust the composition of plating solution, maintain the concentration of main salt at 200-300g/L, boric acid content ≥35g/L, chloride ≤5g/L.
Plating solution impurity contamination
Metallic impurities (iron, copper, etc.) and non-metallic impurities (grease Metal impurities (iron, copper, etc.) and non-metal impurities (grease, polishing paste residue) will trigger pinholes, pockmarks or plating flaking.
Countermeasure: Adopt activated carbon filtration + ion exchange resin treatment, add 0.5-1kg of activated carbon per 1000L of plating solution to adsorb organic impurities.
II. The pretreatment is not complete
Oil / oxide layer residue
The substrate surface oil removal is not clean or insufficient pickling time (<3min), resulting in poor adhesion of the plating layer, easy to peel, peeling 34.
Countermeasures: the use of electrolytic degreasing (current density 5-10A/) + mixed acid. dm²) + mixed acid (HNO₃:HCl=3:1) activation, activation time is extended to 5-8 minutes.
Passivation film is not removed
Aluminum oxide is not completely removed from the surface of aluminum alloy, and the bonding strength of chemical nickel plating layer is reduced by more than 30%.
Countermeasures: the use of secondary zinc deposition process (zincate treatment 2 times, each 30-60 seconds), and in the zinc deposition after the use of alkaline chemical nickel priming.
III. Improper control of process parameters
Abnormal current density
Too high a current density (> 5A / dm ²) leads to scorching of the coating, too low (< 1A / dm ²) triggered by loose plating, white mist.
Countermeasure: Dynamically adjust the current density (2-4A/dm²) according to the temperature of the plating solution and use pulsed power supply to reduce the edge effect.
Temperature and pH fluctuation
Temperature deviation >±2℃ or pH fluctuation >0.3 leads to uneven crystallization and hardness of plated layer.
Countermeasures: Install constant temperature control system (accuracy ±1℃) and use pH automatic compensation device (fluctuation range ≤0.1).
IV. Equipment and operation problems
Failure of filtration system
Insufficient frequency of filtration of plating solution (<2 times/hour) or clogging of filter cartridge, solid particles cause roughness of plating layer (Ra>1.6μm).
Countermeasures: Use 5μm precision filter element, circulate the filtration solution 3-4 times per hour, and clean the anode bag regularly.
Hangers design defects
Poor contact or overloading of hangers (>2dm²/L), resulting in darkening and uneven thickness of plating layer in low current area.
Countermeasures: Optimize the conductive contacts of the hangers (copper silver plating treatment), control the loading amount of 1-1.5dm²/L.
V. Influence of the characteristics of the substrate
Abnormal surface condition of the aluminum alloy
Excessive corrosion of the substrate (pickling time>10min) or rough polishing pattern (Ra>0.4min). (Ra＞0.4μm), resulting in a 50% decrease in the bonding strength of the plating layer.
Countermeasures: Add corrosion inhibitor (e.g. urotropin 0.5g/L) in pickling solution, and add chemical polishing process after mechanical polishing.
Interference of dissimilar metals
Copper, zinc and other alloying elements are dissolved in the plating solution, forming a replacement reaction, which triggers blistering and blistering of the plated layer.
Countermeasure: Pre-plating neutral nickel (thickness 0.5-1μm) or using cyanide pre-plating copper process to isolate the substrate.