[China Aluminum Network] Aiming at the problems of large volatility and great harm to human body in nitric acid retreat process gas used in aluminum alloy electroplating pretreatment, an environmental resignation process was introduced. The formula composition is: 10mL/L concentrated sulfuric acid, 50g/L dezincification agent. Judging from the comparison of resignation effects and test results of coating adhesion, the zinc removal process can completely replace the traditional nitric acid retreat process. The zinc removal process has the characteristics of low concentration, no volatilization, no yellow smoke, and extremely low harm to the human body, and is in compliance with the current requirements of the cleaner production and environmental protection regulations.
Keywords: Zinc removal; Aluminum alloy; Bonds; Pre-treatment Introduction With the rapid development of science and technology, aluminum alloy has become more and more widely used in aerospace, automotive, instrumentation and electronics industries. However, since aluminum alloy is a relatively active metal, its application must be surface functionalized, and electroplating is a good way.
The key to aluminum alloy plating is the pre-treatment process. At present, the zinc leaching process is widely used in industrial production. Since the front immersion zinc process is relatively loose, the aluminum alloy material (such as ADC) with high impurity content cannot guarantee good adhesion to the plating layer. In order to improve the process stability and ensure the product quality, most electroplating plants use two zinc immersion processes to remove the oxide film by zinc immersion and replace it with a zinc layer, and then immerse the zinc layer in 50% nitric acid. Zinc stripping removes the bad zinc layer. The surface exposed after retreating provides a good condition for the second zinc dipping, which fully activates the surface of the aluminum alloy material and guarantees a good bonding force between the substrate and the plating layer.
In the process of nitric acid retreating zinc, there is a large volatilization of the acid mist, and the use process easily generates gas NOx (commonly known as yellow smoke), causing environmental pollution and human hazards, and does not meet environmental protection requirements and should be eliminated.
The development of environmentally friendly zinc-removal technology is to replace nitric acid with less harmful oxidants, while achieving the same effect of dezincification, but also greatly reducing environmental pollution and human hazards. This article describes an environmentally friendly dezincification process and compares the zinc removal mechanism of this process and its zinc removal effect with that of nitric acid and zinc removal to promote the widespread application of environmentally friendly zinc removal processes.
1 Experiment 11 Experimental materials Two types of aluminum alloy materials commonly used in industrial production were used for experiments. The material types were: A356, ADC-12.
1.2 Experimental content 1) Effect of zinc removal. According to the change of time, visual observation 50%. The phenomenon of zinc removal from HNO3 and zinc stripping liquid with AL-ZS1 as the dezincification agent compares the difference in zinc removal effect between the two.
2> The binding force between the substrate and the plating layer. Thermal shock test: Put the plated workpieces at 220°C for 1 h in a box, then take out and immediately throw in cool water to observe if there is blistering or peeling.
Rake test: At the edge of the workpiece after plating, from the base metal to the plating layer, a trowel was used to constrain the plating layer, and the trowel and the surface of the coating were formed at an angle of about 45° to observe whether the plating and the substrate were separated.
1.3 Process Flow and Process The pretreatment and electroplating process for aluminum alloy parts is as follows:
Aluminum alloy workpiece → degreasing → alkaline etching → non-z acid cleaning → one non-cyanide zinc leaching → environmental protection zinc removal → secondary non-cyanide zinc immersion → pre-nickel plating <4 ~ 7μm) → acid copper plating <30~ 40μm) → plated bright nickel (8~12μm) → plated bright nickel <8~12μm) → plated decorative chrome (0.15-0.3μm) → detection.
The zinc removal process adopts a zinc removal agent developed by a company into the AL-ZS1. The dezincification agent is compounded by a certain proportion of oxidants, accelerators, and corrosion inhibitors.
2 Results and Discussion 2.1 The effect of zinc removal compared to the phenomenon of zinc removal.
From the above test results, it can be known that the zinc removal rate of nitric acid is faster, and the zinc layer is generally completely removed in 2~3s, and there is no hydrogen evolution during the process; but the AL-ZS1 zinc removal solution needs 10s to completely remove the zinc layer, and the process Accompanying hydrogen evolution. With the extension of the dezincification time to more than 11s, the two systems do not corrode the aluminum alloy substrate and have the same effect. Therefore, although the rate of dezincification in the two zinc-removal systems is different, it is the same as the final zinc retreat.
2.2 Cohesion Test Plating adhesion tests were performed after electroplating with two different aluminum alloys using different zinc removal processes.
From the above test results, it can be seen that the electroplating strength of the secondary zinc immersion process is significantly better than that of the primary zinc immersion process. In the secondary zincation process, the combination of human [-231 dezincification] and 50 ^ dezincification of the electroplating layer meets the requirements.
3 [-231 zinc-deposition mechanism analysis and component effects 3.1 mechanism ^ 1 ^-281 dezincification solution sulfuric acid provides acidity, and oxidants, accelerators and corrosion inhibitors together to replace the various properties of nitric acid.
When the workpiece with a zinc displacement layer is leached into the 41 231 reject solution, since the electrode potential on the surface of the zinc layer 20 is negative, the sulfuric acid first dissolves the metallic zinc, and after the reaction produces a zinc layer to be dissolved, the remaining sees, & 1 ,! ^ The alloy composition is oxidized into an ion by an oxidizing agent and an accelerator and dissolved in an acid solution. At this time, the hydrogen evolution is almost stopped; later, a protective film is covered on the surface of the exposed aluminum alloy by the combined action of the corrosion inhibitor and the oxidant. To ensure that the substrate is not corroded in the acid.
Since the acidity and oxidizing power of the 1231 stripper is lower than that of the nitric acid, although the speed of zinc removal is slower than that of nitric acid, the zinc layer can be removed from the end more cleanly, and the substrate and the plating layer after plating are ensured to be good. Binding force.
3.2 The role of components 3.2.1 The role of only 2304 only 2304 can provide acidity to dissolve the metal zinc, 92304 directly affect the amount of zinc zinc dissolution speed. The experiment of dezincification was performed on the human 231 dezincification process at different concentrations of 02304, and the relationship between the dezincification time (the time required for the color of the zinc layer to fade to expose the color of the aluminum material) and the concentration of 02304 was recorded.
As can be seen from Fig. 1, when ^(??æ²)<5 paws 17[, the rate of dezincification is slow, and the dezincification time needs to be very long. At this time, the hydrogen evolution rate on the surface of the workpiece is slow and non-uniform, with the gradual increase of 4112504, The rate of dezincification accelerates, and the hydrogen evolution rate is 4415011^1, the rate of zinc removal does not change significantly and tends to be constant. As the acidity is high, the surface of the aluminum alloy substrate after dezincification is over-etched. Therefore, 4 and 300 should not be too high, considering the speed and effect of zinc removal, the better control range is between 5 to 15 melons!/!^.
3.2.2 The role of dezincification agent Dezincification agent & -231 contains oxidant, accelerator and corrosion inhibitor, mainly play the role of oxidation, dissolution and protection of the substrate, its mass concentration directly affects the speed of the zinc displacement layer. Experiments were conducted on the effects of zinc removal on human zinc removal agent at different dosages, and the relationship between the zinc removal time and the quality concentration of zinc removal agent was recorded.
When #(from - strong) 〈40, the rate of zinc removal is slow, the main performance is that after the hydrogen evolution stops, the color of the zinc layer is difficult to retreat, and the color of aluminum cannot be exposed; with the gradual increase of 4, the rate of zinc removal follows The speeding up of the zinc layer quickly retreats; when the 乩V乩-281]> 60V [when the zinc removal rate does not change significantly, it tends to be stable. Therefore, the best control range for People Seven-281 is 40-60g/L.
4 Conclusions 1) The aluminum alloy de-zinc process introduced in this article can completely replace the traditional zinc nitrate de-zincification process, and the dezincification fluid is stable and has a long service life, which is suitable for electroplating production needs, especially for automatic line production.
2) The aluminum alloy dezincification process has the characteristics of no volatilization, no yellow smoke, and extremely low harm to the human body, and is in line with the current requirements for clean production and environmental protection regulations.
3> The aluminum alloy dezincification process solution has a small amount, the waste water treatment is simple, and does not require the use of ventilation equipment, which reduces the production cost to a certain extent and meets the requirements of environmental protection and is worthy of promotion.
The series activated carbon is mainly used for the purification of drinking water, deep degree treatment of industrial of super purified water. The organic substances, which are harmful to human health and environment, can be effectively removed.
l Technical Properties of Our Product
In recent years, Huahui Company aims at developing the deeply purify craft of domestic drinking water and property of water quality. Our products have the technological property as follows:
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Main Technical Parameters of Water Treatment
Pellet Activated Carbon
Index
Moisture
Hardness
Ash
Iodine
Methylene
Blue
Density
Floater
PH
Value
Type
(%)
(%)
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(mg/g)
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HA-1.5
≤3
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480±20
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