Novel process for direct chemical nickel plating of aluminum alloy

Abstract

The invention discloses a novel process for direct chemical nickel plating of an aluminum alloy. The novel process comprises the following steps: sequentially carrying out oil removal and wax removal treatment on an aluminum alloy workpiece, and then washing with water; sequentially carrying out weak corrosion treatment, descaling, water washing and activating treatment; directly carrying out chemical nickel plating; the invention relates to the technical field of aluminum alloy nickel plating, and in the new process, a special activating agent prepared from a strong oxidant and a weak reducing agent is adopted, so that the aluminum alloy can be directly subjected to chemical nickel plating after being subjected to chemical oil removal, acid pickling and activating solution treatment without secondary zinc immersion treatment; 17 procedures of a traditional process are simplified into 7 procedures, the technological process is greatly shortened, the production efficiency is improved, as the activating agent does not corrode workpieces and is high in uniform plating capacity, the problems that in the traditional process, due to grain boundary segregation enrichment, plating exposure and blistering are prone to occurring in a low-potential area are effectively solved, and the one-time qualification rate is increased to 98% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field, in particular to a novel process for direct chemical nickel plating of aluminum alloy. BACKGROUND

[0002] With the rapid development of the fields of aviation, aerospace, ship, electronics, medical devices, automobile industry, etc., the demand for lightweight materials is increasing, and the electroplating and chemical plating technology of aluminum alloy as a lightweight material is rapidly developing. In the traditional process of chemical nickel plating of aluminum alloy, it has always been limited that secondary zinc immersion treatment must be carried out before chemical plating. This traditional process has many drawbacks, such as the electrolyte is easily affected by harmful impurities in the secondary zinc immersion solution, resulting in unstable plating layer quality; the operation procedure of chemical nickel plating is complex and difficult, and the chemical nickel plating solution needs to be frequently adjusted and replaced, which increases the production cost and operation difficulty; in addition, the zinc precipitant used in the traditional process contains a large amount of heavy metal ions and toxic cyanide ions, which not only causes serious environmental pollution, but also is strictly limited by the environmental protection department. Therefore, it is of great practical significance to develop a new process that can break through the shackles of traditional process and realize direct chemical nickel plating of aluminum alloy. SUMMARY

[0003] In view of the shortcomings of the prior art, the present application provides a novel process for direct chemical nickel plating of aluminum alloy, which solves the problems of complex operation, long process and low yield of the existing zinc immersion and nickel plating process.

[0004] To achieve the above purpose, the present application is realized by the following technical scheme: a novel process for direct chemical nickel plating of aluminum alloy, comprising the following steps:

[0005] S1, sequentially performing oil removal, wax removal and water washing on the aluminum alloy workpiece;

[0006] S2, performing chemical oil removal on the aluminum alloy workpiece and then water washing;

[0007] S3, sequentially performing weak etching treatment, descaling and water washing on the aluminum alloy workpiece, and then using an activator to activate the aluminum alloy workpiece after water washing;

[0008] S4, directly performing chemical nickel plating on the activated aluminum alloy workpiece;

[0009] S5, performing post-plating treatment on the aluminum alloy workpiece after nickel plating;

[0010] The activator comprises a strong oxidizing agent and a weak reducing agent, the temperature of the activation treatment is 25-50 DEG C, and the time is 1-3 min.

[0011] Preferably, the plating solution for electroless nickel plating in step S4 comprises 35 g / L of nickel sulfate, 9 g / L of sodium hypophosphite, 20 g / L of sodium citrate, and 15 g / L of sodium acetate, and the plating solution has a pH value of 4.5 and a temperature of 80-82°C.

[0012] Preferably, the post-plating treatment comprises recovery, water washing, and drying.

[0013] Preferably, the wax removal process in step S1 uses ultrasonic wax removal, and the temperature is 55-70°C and the time is 1-3 min.

[0014] Preferably, the water washing process is performed after the weak etching treatment of the aluminum alloy workpiece in step S3.

[0015] Preferably, the temperature of the water washing process in each step is 15-30°C and the time is 10-15 s.

[0016] Preferably, the electroless nickel plating layer has a thickness of 80-200 μm, a microhardness of 500-600 HV, and a phosphorus content of 8-10%.

[0017] Advantages

[0018] The present application provides a novel process for direct electroless nickel plating of aluminum alloy, which has the following advantages:

[0019] The novel process uses a special activator prepared from a strong oxidizing agent and a weak reducing agent, so that the aluminum alloy does not need to be treated by secondary zinc immersion, but only needs to be treated by chemical degreasing, pickling, and activation, and then can be directly subjected to electroless nickel plating, thereby simplifying the traditional process of 17 steps into 7 steps, greatly shortening the process flow, and improving the production efficiency.

[0020] The process has stable, uniform, dense, and bright plating quality, and the plating layer has a thickness of 80-200 μm, a microhardness of 500-600 HV, a phosphorus content of 8-10%, and strong adhesion to the substrate, and can withstand corrosion tests for more than 66 hours (CASS test). In addition, since the activator does not corrode the workpiece and has strong uniform plating ability, it can completely plate very small pinholes and slag holes, effectively avoiding problems such as easy plating exposure and bubbling in low-potential areas caused by grain boundary segregation in the traditional process, and increasing the one-time qualification rate to more than 98%.

[0021] The novel process reduces pollution emissions and reduces pollution of the plating solution, and the bath solution can be reused for more than 15 cycles after analysis and adjustment, thereby reducing the frequency of plating solution replacement and reducing production costs. In addition, due to the increase in the one-time qualification rate, additional processes such as repating, re-polishing, and re-electroplating nickel are reduced, further reducing costs.

[0022] The new process is suitable for aluminum alloy, aluminum alloy die casting, computer heat sink, hard disk and other aluminum alloy products, and can be applied to chemical nickel plating roll and hanging plating production line, and has wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The schematic diagram of the base and the plating layer metallographic structure obtained by the new process of direct chemical nickel plating on aluminum alloy (100 times magnification). DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] Please refer to Figure 1 The present application provides a technical solution: a new process of direct chemical nickel plating on aluminum alloy, comprising the following steps:

[0026] S1, sequentially performing oil removal, wax removal and water washing on the aluminum alloy workpiece;

[0027] S2, performing chemical oil removal and water washing on the aluminum alloy workpiece;

[0028] S3, sequentially performing weak corrosion treatment, descaling and water washing on the aluminum alloy workpiece, and then performing activation treatment on the aluminum alloy workpiece by using an activator after water washing;

[0029] S4, directly performing chemical nickel plating on the activated aluminum alloy workpiece;

[0030] S5, performing post-plating treatment on the aluminum alloy workpiece after nickel plating;

[0031] The activator comprises a strong oxidizing agent and a weak reducing agent, the temperature of the activation treatment is 25-50℃, and the time is 1-3 min.

[0032] In this embodiment, the plating solution for chemical nickel plating in step S4 comprises nickel sulfate 35g / L, sodium hypophosphite 9g / L, sodium citrate 20g / L and sodium acetate 15g / L, the pH value of the plating solution is 4.5, and the temperature is 80-82℃.

[0033] In this embodiment, the post-plating treatment comprises recovery, water washing and drying.

[0034] In this embodiment, the wax removal process in step S1 adopts ultrasonic wax removal, the temperature is 55-70℃, and the time is 1-3 min.

[0035] The embodiment is further provided with a water washing procedure after the weak etching treatment of the aluminum alloy workpiece in step S3.

[0036] The embodiment is further provided with a water washing procedure in each step, with a temperature of 15-30℃ and a time of 10-15s.

[0037] The embodiment is further provided with a plating layer of the electroless nickel plating with a thickness of 80-200μm, a microhardness of 500-600HV, and a phosphorus content of 8-10%.

[0038] By the skilled in the art, the parts in the case are sequentially connected, and the specific connection and operation sequence should be referred to the working principle below, and the detailed connection means is the commonly known technology in the art, and the working principle and process are mainly introduced below.

[0039] The embodiment is further provided with a water washing procedure in each step, with a temperature of 15-30℃ and a time of 10-15s.

[0040] The aluminum alloy direct electroless nickel plating activator can be used for a long time after replenishment and adjustment, and each liter of the activator can treat workpieces of 10-15 square meters. The activator solution is stable, easy to maintain, and only needs to be supplemented with concentrated liquid and adjusted with ammonia water for PH value. The consumption of the activator is 100d㎡ / 100-150ml. If the workpieces are taken out, the activator can be added to the specified volume according to the volume after the decrease.

[0041] The following are the aluminum alloy direct electroless nickel plating detection data:

[0042] 1. Plating layer hardness: microhardness 500-600

[0043] 2. Coating phosphorus content: 8-10%

[0044] 3. Coating uniformity: about 5%

[0045] 4. Coating thickness: 80-200 microns

[0046] 5. Coating and substrate adhesion: The test piece uses A356 die-cast aluminum alloy, after chemical nickel plating, the workpiece is heated to 200°C in an oven, and kept at constant temperature for 2 hours, then repeatedly quenched in room temperature water, no blistering is found in the coating, and the file method, saw blade method, and adhesive tape method tests are all better than the secondary zinc immersion process.

[0047] 6. Corrosion resistance

[0048] Corrosion resistance test exceeds 66 hours or more. (CASS test)

[0049] The substrate and coating metallographic structure photos obtained under the new process specification and flow of aluminum alloy direct chemical nickel plating (enlarged 100 times) are shown in Figure 1

[0050] In summary, the advantages of applying the new technology of aluminum alloy direct chemical nickel plating are: the secondary zinc displacement process can be omitted, making technical management, plating solution management, and wastewater treatment simple, the aluminum hub only needs to be washed once or not washed after activation, and then directly chemical nickel plating or flash chemical nickel plating can be performed, which can enhance the coating adhesion, reduce pores, and improve corrosion resistance. Using the activator for aluminum alloy direct chemical nickel plating or flash chemical nickel plating completely overcomes the shortcomings of intergranular corrosion, surface without coating, etc. caused by residual liquid in the areas such as pinholes, sand eyes, small process holes, and blind holes on the surface of aluminum alloy workpieces. The biggest advantage of using the aluminum alloy direct chemical nickel plating activator is that there is a coating on the part immersed by the activator, which completely solves the problem of blistering in the low potential area caused by the composition segregation and enrichment at the grain boundary of die-cast materials in the aluminum alloy chemical nickel plating process. In a humid corrosive environment, when the corrosive atmosphere reaches the substrate through the pinholes and other defects on the surface layer, the zinc displacement layer becomes anode relative to the plated metal and aluminum substrate, which will cause the zinc to be subjected to transverse corrosion, white powder-like substances appear between the aluminum hub substrate and the coating, causing intergranular corrosion of the substrate, and eventually leading to the problem of blistering and peeling of the coating.

[0051] ​It has to be noted that, in the present document, the terms "first", "second", etc. merely serve to identify different entities or actions and do not necessarily require or imply any actual relationship or order between these entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. In other words, without further restriction, reference to elements will not, without more limitations, exclude additional, unrecited elements of a process, method, article, or apparatus.

[0052] While embodiments of the application have been shown and described, it is to be understood that the application is not limited to these embodiments. Rather, it is the intention to cover any variations and modifications, provided they fall within the scope of the application as defined by the appended claims and their equivalents.

Claims

1. A novel process for direct electroless nickel plating of aluminum alloys characterized in that, The method comprises the following steps: S1, sequentially performing oil removal, wax removal and water washing on the aluminum alloy workpiece; S2, performing chemical oil removal and water washing on the aluminum alloy workpiece; S3, sequentially performing weak corrosion treatment, descaling and water washing on the aluminum alloy workpiece, and then performing activation treatment on the aluminum alloy workpiece by using an activator after water washing; S4, directly performing chemical nickel plating on the activated aluminum alloy workpiece; S5, performing post-plating treatment on the aluminum alloy workpiece after nickel plating. The activator comprises a strong oxidant and a weak reducing agent, the temperature of the activation treatment is 25-50 DEG C, and the time is 1-3 min.

2. A novel process for direct electroless nickel plating of aluminum alloys as claimed in claim 1, wherein, The plating solution for the chemical nickel plating in step S4 comprises nickel sulfate 35 g / L, sodium hypophosphite 9 g / L, sodium citrate 20 g / L and sodium acetate 15 g / L, the pH value of the plating solution is 4.5, and the temperature is 80-82 DEG C.

3. A novel process for direct electroless nickel plating of aluminum alloys as claimed in claim 1, wherein, The post-plating treatment comprises recovery, water washing and drying.

4. A novel process for direct electroless nickel plating of aluminum alloys as claimed in claim 1, wherein, The wax removal process in step S1 adopts ultrasonic wax removal, the temperature is 55-70 DEG C, and the time is 1-3 min.

5. A novel process for direct electroless nickel plating of aluminum alloys as claimed in claim 1, wherein, The water washing process is performed after the weak corrosion treatment on the aluminum alloy workpiece in step S3.

6. A novel process for direct electroless nickel plating of aluminum alloys as claimed in claim 5 wherein, The temperature of the water washing process in each step is 15-30 DEG C, and the time is 10-15 s.

7. A novel process for direct electroless nickel plating of aluminum alloys as claimed in claim 1, wherein, The plating layer of the chemical nickel plating has a thickness of 80-200 mu m, a microhardness of 500-600 HV and a phosphorus content of 8-10%.

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