The tin-drilled alloy plating containing Sn70%～80% and C020%～30% has the same appearance and color as the chromium plating house and is often used as a substitute for chrome plating. However, this coating has no chrome plating hardness and high abrasion resistance and can only be used as a decorative generation chrome coating.
There are many kinds of plating solutions for this kind of alloy, but most of them are not reported because of confidentiality. The typical solution of pyrophosphoric acid system is: Potassium pyrophosphate 2509/L, Cobalt sulfate l09/L~209/L, Sulfuric acid Tin l09/L~209/L, additive l00mL/L, pH8~9, temperature 35°C~45°C, current MILIA 0.8A/dm2~2A/dm2, cathode movement 20 times/min. Due to the actual electroplating production, the consumption of tin salts and cobalt cerium is not equal. Under normal circumstances, the ratio of stannous sulfate to cobalt sulfate is (2 to 3): 1 The proportion of tin and cobalt in the bath can be maintained without misalignment. In addition, the molar ratio of pyrophosphate ion to tin ion+cobalt ion in the plating solution is controlled at (2 to 2.5):1 to maintain the stability of the plating solution.
In the actual tin-cobalt alloy electroplating production process, common faults and exclusion methods are as follows.
1 Part coating in the high current density area cloud fog, low current density area exposed
Examination revealed that the bath was slightly turbid. The reason for the deterioration of the bath was that due to the high frequency of the parts entering and leaving the plating bath, the diluting effect and the carry-out loss of the water brought into the plating were neglected, and the potassium pyrophosphate and the like were not increased accordingly. The amount of added, leading to its low content. At the same time, the content of tin and cobalt ions in the tank is also low and the ratio is imbalanced. This led to the emergence of this failure.
Analytical test at this time the bath composition: potassium pyrophosphate 1609 / L, stannous sulfate 139 / L, barium sulfate 89 / L, by adding solution components to the content of the process formulation, the failure was ruled out.
If there is no analysis of the assay conditions, it can be adjusted empirically or by using a Hall-effect test strip, or by trial-and-error. For example, add potassium pyrophosphate 409/L to 809/L, test the pH of the bath, and then use hydrogen. Potassium oxide kinematics pH value to about 8.8, trial plating, if the entire rack parts on the disappearance of white fog or only a small amount of zero, and the low current density coating is still poor coverage, you can add appropriate amount of cobalt sulfate With additives, until the Tao disappears. At this time, if the deposition rate is very slow, a shift of tin salt and cobalt salt will be added to the daily consumption, and this failure phenomenon can be eliminated.
2 Black parts appear in high current density area (tip or edge) of the plated part
The reason for this failure is the low additive content and high current density. This phenomenon can be eliminated after adding additives and adjusting the current density.
3 plating color black, not chrome
This failure may be due to: the bath temperature is low; the cobalt ion content in the bath is relatively high; The exclusion method is to check the temperature of the bath first, and then add one shift of tin salt, cobalt salt and potassium pyrophosphate, etc., and test it through a Hull cell or a small plating bath. If the fault is not eliminated, then add the appropriate amount of sulfuric acid. Tin eliminates this failure.
4 bath turbidity
The reason why the turbidity of the bath occurs is generally caused by the oxidation of divalent tin ions in the bath, especially when the graphite anode is used. Hydrogen peroxide can be added to the production process.
5 plating discoloration
This kind of alloy coating itself is poor in its anti-tarnishing property, so it needs to be passivated after plating in order to improve the discoloration resistance of this coating.
There are many kinds of plating solutions for this kind of alloy, but most of them are not reported because of confidentiality. The typical solution of pyrophosphoric acid system is: Potassium pyrophosphate 2509/L, Cobalt sulfate l09/L~209/L, Sulfuric acid Tin l09/L~209/L, additive l00mL/L, pH8~9, temperature 35°C~45°C, current MILIA 0.8A/dm2~2A/dm2, cathode movement 20 times/min. Due to the actual electroplating production, the consumption of tin salts and cobalt cerium is not equal. Under normal circumstances, the ratio of stannous sulfate to cobalt sulfate is (2 to 3): 1 The proportion of tin and cobalt in the bath can be maintained without misalignment. In addition, the molar ratio of pyrophosphate ion to tin ion+cobalt ion in the plating solution is controlled at (2 to 2.5):1 to maintain the stability of the plating solution.
In the actual tin-cobalt alloy electroplating production process, common faults and exclusion methods are as follows.
1 Part coating in the high current density area cloud fog, low current density area exposed
Examination revealed that the bath was slightly turbid. The reason for the deterioration of the bath was that due to the high frequency of the parts entering and leaving the plating bath, the diluting effect and the carry-out loss of the water brought into the plating were neglected, and the potassium pyrophosphate and the like were not increased accordingly. The amount of added, leading to its low content. At the same time, the content of tin and cobalt ions in the tank is also low and the ratio is imbalanced. This led to the emergence of this failure.
Analytical test at this time the bath composition: potassium pyrophosphate 1609 / L, stannous sulfate 139 / L, barium sulfate 89 / L, by adding solution components to the content of the process formulation, the failure was ruled out.
If there is no analysis of the assay conditions, it can be adjusted empirically or by using a Hall-effect test strip, or by trial-and-error. For example, add potassium pyrophosphate 409/L to 809/L, test the pH of the bath, and then use hydrogen. Potassium oxide kinematics pH value to about 8.8, trial plating, if the entire rack parts on the disappearance of white fog or only a small amount of zero, and the low current density coating is still poor coverage, you can add appropriate amount of cobalt sulfate With additives, until the Tao disappears. At this time, if the deposition rate is very slow, a shift of tin salt and cobalt salt will be added to the daily consumption, and this failure phenomenon can be eliminated.
2 Black parts appear in high current density area (tip or edge) of the plated part
The reason for this failure is the low additive content and high current density. This phenomenon can be eliminated after adding additives and adjusting the current density.
3 plating color black, not chrome
This failure may be due to: the bath temperature is low; the cobalt ion content in the bath is relatively high; The exclusion method is to check the temperature of the bath first, and then add one shift of tin salt, cobalt salt and potassium pyrophosphate, etc., and test it through a Hull cell or a small plating bath. If the fault is not eliminated, then add the appropriate amount of sulfuric acid. Tin eliminates this failure.
4 bath turbidity
The reason why the turbidity of the bath occurs is generally caused by the oxidation of divalent tin ions in the bath, especially when the graphite anode is used. Hydrogen peroxide can be added to the production process.
5 plating discoloration
This kind of alloy coating itself is poor in its anti-tarnishing property, so it needs to be passivated after plating in order to improve the discoloration resistance of this coating.