The method of plating a layer of nickel on metal or certain non-metals by electrolytic or chemical methods is called nickel plating. Nickel plating is divided into electroplated nickel and chemical nickel plating. Nickel-plated aluminum parts are popular with manufacturers and consumers for their excellent appearance and cost-effectiveness. Aluminum is naturally positively charged and compatible with nickel. Therefore, nickel-plated aluminum is more straightforward and more cost-effective.
Flowing this article, you will learn the full information about Nickel Plating and Nickel plating aluminum.
Table of Contents
Types of Nickel Plating
The leading nickel plating solutions are sulfate, chloride, citrate, and fluoroborate. Among them, the sulfate type (low chloride), called Watts (Watts) nickel plating solution, is the most commonly used industry. Several different nickel plating solutions in the physical properties of the nickel layer were obtained, as listed in Table 2-3-45. Aminosulfonate type and fluoroborate type are suitable for plating thick nickel or electroforming. Citrate type is suitable for direct nickel plating on zinc die castings. The cost of these plating solutions is relatively high.
◆ General nickel plating (dark plating)
General plating is also called the dark nickel process. According to the performance and usage of plating solution, available nickel plating can be divided into low concentration preplating solution, general plating solution, watt solution, and barrel plating solution.
Preplating solution: Pre-plating can ensure good bonding between the layer, the copper-iron substrate, and the subsequent copper plating layer.
Typical solution: The plating solution has good electrical conductivity, can be plated at a lower temperature, saves energy, and is easy to use.
Watt solution: It is suitable for plating small parts, but the solution must have good electrical conductivity and covering ability.
◆ Bright Nickel
Bright nickel plating has many advantages. Not only can it eliminate the heavy polishing process, improve the operating conditions, and save plating and polishing materials, but it also can improve the hardness of the plated layer and facilitate automated production, but the bright nickel plating layer contains sulfur, internal stress, and brittleness, and the corrosion resistance is not as good as the dark nickel plating layer.
The general content of high sulfur nickel is 0.12~~0.25%. This kind of nickel has higher electrochemical activity than copper, copper-tin, dark nickel, bright nickel, semi-bright nickel, chromium, etc. The principle is that the upper layer of bright nickel has higher sulfur content than the lower layer of semi-bright nickel so that the potential difference between the two layers is 100~~140mV, which makes the double layer of nickel change from the longitudinal corrosion of the single layer of nickel to transverse corrosion and constitutes the electrochemical protection for the steel substrate.
◆ Nickel Sealing
Nickel seal is a composite nickel plating layer formed by adding insoluble solid particles (Sio2, etc.) with a diameter of 0.01~~1um to a general bright nickel solution and co-depositing these particles with nickel with the help of a suitable co-deposition accelerator. When the chromium layer is deposited on the surface of this composite nickel plating layer, chromium cannot be deposited on the surface of the particles because the solid particles on the surface of the composite nickel plating layer are not electrically conductive. Under the corrosive medium, chromium and nickel form a corrosive cell, with a chromium layer as cathode and an exposed nickel layer at the micropore as an anode, thus changing the corrosion pattern of large cathode and small anode. The corrosion pattern of the large cathode and the small anode is changed so that the corrosion current is dispersed to almost the whole nickel plating layer, thus preventing the generation of large and deep corrosion grooves and pits directly through the base metal and reducing the corrosion rate of the plating layer. The lateral development thus protects the base metal and significantly improves the corrosion resistance of the plating layer.
Satin nickel is also called satin nickel. Satin nickel is not fundamentally different from the nickel sealing process. It has a satin appearance and does not shine like chrome plating or bright nickel plating, so the human eye will not feel fatigued after looking at it. This type of plating is widely used on the surfaces of automobile reflectors, interior viewing parts of vehicles, medical and surgical instruments, machine tool parts, eyeglass frames, etc.
◆High Stress Nickel
Adding the right amount of additives to a specific nickel plating solution can obtain a highly stressed nickel layer prone to cracking into microcracks.
High-stress nickel is a nickel layer of about 1um on the surface of the bright nickel. Because of the high internal stress of high-stress nickel, after plating 0.2~~0.3um ordinary chromium layer on its surface, the interaction between the chromium layer and high-stress nickel stress results in a large number of micro-cracks in the high-stress nickel layer. It leads to the formation of uniform micro-cracks on the surface of the chromium layer. Under the corrosive medium, these cracked areas dematerialize into numerous microcells so that the corrosion current is dispersed at the microcracks. Thus the corrosion resistance of the whole layer is significantly improved.
◆Multi-layer nickel plating
Multi-layer nickel plating is to obtain two or three layers of nickel plating on the same substrate with different plating solution compositions and process conditions, to increase the corrosion resistance of the nickel layer without increasing the thickness of the nickel layer or reducing the nickel layer. The most popular multi-layer nickel/chromium combination systems used in production are
Double nickel Semi-bright nickel/bright nickel/chromium
Triple nickel semi-bright nickel/high sulfur nickel/bright nickel/chromium
Semi-bright nickel/bright nickel/nickel seal/chromium (microporous chromium)
Semi-bright nickel/bright nickel/high stress nickel/chromium (micro-crack chromium)
◆ Sulfamate Nickel Plating
The main advantage of sulfamate nickel plating is the low stress of the resulting plated layer and the fast deposition of the plating solution, but it is more expensive. It is used for electroforming and nickel plating before gold plating of printed circuit boards.
Citrate Nickel Plating
The citrate nickel plating process is mainly used for plating zinc die castings. The main maintenance measures are: to control the ratio of nickel sulfate to citrate at 1:1.1~~1.2. The temperature should not be too high to prevent the decomposition of citrate, strictly control the pH value, and use an impulse current (2~3A/dm2) for the parts to enter the tank to ensure good bonding. The application of citrate nickel plating is not yet widespread, and few manufacturers have successfully produced it.
Electroplated nickel and Electroless nickel plating (chemical nickel plating)
Electroplated nickel is the deposition of a uniform, dense nickel layer on the cathode (plated part) in an electrolyte consisting of nickel salt (called the main salt), conductive salt, pH buffer, and wetting agent, with nickel metal at the anode and the plated part at the cathode, by passing a direct current.
Electroless nickel plating is the technology of depositing a metallic coating on the metal surface by an autocatalytic chemical reaction in a solution where metal salts and reducing agents are present together.
Characteristics, properties, and uses of electroplated nickel.
1、 The stability of the electroplated nickel layer in the air is very high because metallic nickel has a strong passivation ability. It can quickly generate a fragile passivation film on the surface, which can resist the corrosion of the atmosphere, alkali, and certain acids. The stability of the electroplated nickel layer in the air is high, and the plating has a strong passivation ability, which can quickly generate a thin passivation film on the surface of the substrate and can resist the corrosion of the atmosphere, alkali, and certain acids. It can be used as a protective decorative coating to protect the steel substrate. Zinc die castings, aluminum alloy, and copper alloy from corrosion.
2、Electroplated nickel crystals are excellent and have excellent polishing properties. A polished nickel plating layer can get a mirror-like appearance while keeping it in the atmosphere for a long time. Therefore, the electroplated layer is often used for decoration and a more beautiful appearance.
3、 The nickel plating layer is relatively high hardness and can improve the wear resistance of the product surface. The printing industry is often used to improve the hardness of the surface of the lead plating layer. Due to the high chemical stability of nickel metal, some chemical equipment is also commonly used in thicker town plating layers to prevent corrosion by the medium. The nickel plating layer is also widely used in functional aspects, such as repairing worn, corroded parts and using brush plating technology for local plating. The Electroforming process is used to manufacture electroforming plates and record molds and other molds for the printing industry.
4、Thick nickel plating layer has good wear resistance and can be used as a wear-resistant plating layer. Especially in recent years, the development of composite plating can be deposited with wear-resistant particles of composite nickel plating, its hardness and wear resistance is higher than the nickel plating layer. If graphite or graphite fluoride is used as dispersed particles, the obtained nickel-graphite or nickel-graphite fluoride composite plating has good self-lubricating properties. It can be used as a lubricating plating layer. Black nickel plating is also widely used as the coating of optical instruments or decorative plating layer.
5、Nickel plating has a wide range of applications. It can be used as a protective decorative plating in steel, zinc die castings, aluminum, and copper alloy surface, to protect the substrate material from corrosion or bright decorative role; also often used as an intermediate layer of another plating.
6、With a thin layer of chromium on it or a layer of imitation gold plating, its corrosion resistance is a better, more beautiful appearance. Regarding functional applications, nickel plating on parts in particular industries is about 1~3mm thick for restoration purposes. Especially in the continuous casting crystallizer, electronic components surface of the mold, die-casting die of alloy, complex shape of the aerospace engine parts and miniature electronic components manufacturing and other parties are increasingly widely used.
7、In electroplating, because electroplated nickel has many excellent properties, its processing volume is second only to electroplated zinc, and its consumption accounts for about 10% of total nickel production.
Characteristics, performance, and uses of Electroless nickel plating.
1, thickness uniformity and good uniform plating ability are significant characteristics of chemical nickel plating. One of the reasons for its wide application is that chemical nickel plating avoids the uneven thickness of the plating layer due to uneven current distribution. When chemical plating, as long as the surface of the parts and the plating solution are in contact, can replenish the consumed ingredients in the plating solution in time, and the thickness of the plating layer of the plated parts is the same, even if the grooves, gaps, blind holes.
2, the plated parts will not seep hydrogen, no hydrogen embrittlement, and no need to remove hydrogen after chemical nickel plating.
3、. The function of many materials and parts, such as corrosion resistance and high-temperature oxidation resistance, is better than an electroplated nickel.
4、It can be deposited on the surface of various materials, such as steel, nickel-based, zinc-based, aluminum, glass, ceramics, plastics, semiconductors, and other materials, thus creating conditions for improving the performance of these materials.
5、No need for DC motor or control equipment is required for general plating.
6、Low heat treatment temperature, as long as below 400 ℃ after different holding times, can get different corrosion resistance and wear resistance. Therefore, especially suitable for complex shapes, the surface requirements of wear and corrosion resistant parts of the functional plating, etc.
Classification of Electroless nickel plating.
1、According to the PH value of the plating solution classification, there are three acidic, neutral, and alkaline categories.
Peal by the deposition temperature classification: low temperature, medium temperature, high temperature three categories.
Alloy by composition: low phosphorus, medium phosphorus, and high phosphorus.
Singing by reductant: Ni-P, Ni-B, etc.
Manufacturers increasingly accept electroless nickel plating for its excellent plating properties, such as high hardness, wear resistance, and corrosion resistance. The medium phosphorus chemical plating layer, the plating performance is as follows:
|Phosphorus content [ω(P)]||6%~9%|
|Microstructure||Amorphous Ni-P alloy, non-magnetic|
|Hardness||450～550HV(45～48HRC) in plated state 950～1050HV after heat treatment|
|Bonding strength||400 MPa or more on steel or aluminum, much higher than electroplated nickel and chromium|
|Internal stress:||less than 7MPa on steel|
|Corrosion resistance||6～8μm can pass the 24h9 continuous salt spray test with 5% mass fraction NaCl solution|
The process of Electroless nickel plating
Chemical nickel plating of stainless steel parts (drive shaft, engagement parts, dynamic fit parts, etc.) can improve the uniformity and self-lubricating properties of the plating, which is better than electrochromic plating. However, the chemical nickel plating of stainless steel is often caused by poor pretreatment, and the combination of plating and substrate is not ideal, which becomes an urgent problem in current production.
Process flow: mechanical polishing → degreasing → chemical degreasing → hot water washing → electrochemical degreasing → hot water washing → cold water washing → 30% HCl → cold water washing → 20% HCl (50 ℃) → cold water washing → flash nickel plating → chemical nickel plating.
Improved process flow: polishing and degreasing process with the same process → mixed acid film removal (25% HCl + 8% HNO3 + 10% HF) → cold water washing → activation (10% HCl + 5% NH4F, 60 ℃) → hot water washing → chemical nickel plating.
Advantages of the improved process: ① the use of mixed acid to remove insoluble FeCrO4 oxide film, Si, SiO2 on the surface of stainless steel so that the chemical activity of the substrate surface is enhanced; ② process simplification, to avoid the new surface of stainless steel re-oxidation; ③ increase the preheating process of the substrate to eliminate the stress generated by the temperature difference between the plating and substrate. Therefore, chemical nickel plating and substrate bonding are good, plating speed, etc.
Application of Electroless nickel plating
Chemical nickel plating has a wide range of applications in various fields with its excellent performance, such as aerospace, automotive, chemical, oil and gas, food processing, mining, military, electronic computer, medical equipment, etc.
Substrates that can plate with nickel
Steel substrates Aluminum substrates
Copper alloy substrates Zinc alloy substrates Stainless steel substrates
The most fundamental difference between electroless nickel plating and electroplating
1. Electroplating requires an applied current and anode, while chemical nickel plating relies on the autocatalytic reaction that occurs on the metal surface.
2. Different plating speed
Electroplating is faster than chemical plating because of the applied current; for the same thickness as nickel plating, electroplating is faster than chemical plating.
3. Environmental protection is not the same
Most additives used in chemical nickel plating are food-grade and do not use harmful substances such as lead, cadmium, and cyanide, so chemical nickel plating is more environmentally friendly than chemical nickel plating.
4. Even plating ability is strong or weak
As long as can soak the plating solution and the solute exchange is sufficient, the chemical nickel plating layer will be uniform and almost achieve an imitation effect. In contrast, electroplated nickel will be weaker than chemical nickel plating because of the influence of current density.
5. Deep plating ability has high and low
Theoretically, chemical nickel plating can plate the whole surface of any shape of the workpiece, but electroplated nickel can’t plate the whole surface of some complicated workpiece shape well.
6. Gap in bonding force of plating layer
The bonding force of the chemical nickel plating layer is generally higher than that of the electroplated nickel layer.
Advantages and disadvantages of electroplating nickel and electroless nickel plating
Electroplating nickel is to immerse the parts in a solution of nickel salts as the cathode and nickel metal plate as the anode. After the DC power supply, the metal nickel plating will be deposited on the parts.
The advantages of electroplating nickel are that the plated layer is meticulously crystallized, smooth and bright, with low internal stress and strong bonding with the ceramic metallization layer.
The disadvantages of electroplating nickel are.
① by the cleanliness of the metalized porcelain parts’ surface and the plating solution’s purity, resulting in more defects in the metalized porcelain parts after platings, such as peeling, blistering, pockmarks, black spots, etc.
② extremely susceptible to plating hanging tools and different positions in the plating cylinder, resulting in poor plating ability, in addition to metalized porcelain parts between each other, will also cause the surface of the porcelain parts with the phenomenon of Yin and Yang
③ The shape of complex or small deep holes or blind holes in the porcelain parts can not get a better plating surface.
④ needs to use nickel wire bundle metalized porcelain parts; producing complex shapes, small size, and many cases take a lot of labor.
Chemical nickel plating
chemical nickel plating is a self-catalytic reduction deposition of nickel layer on the surface of activated parts by using a reducing agent without adding an external current. The process will continue automatically when the nickel layer is deposited on the surface of activated parts because nickel has the self-catalytic ability. Generally, chemical nickel plating yields an alloy coating, commonly Ni-P and Ni-B alloy.
The advantages of chemical nickel plating are no current power supply equipment, uniform, and dense thickness, few pinholes, good uniformity, strong simulation ability, ability to deposit on the surface of complex parts, substantial, profound plating ability, good corrosion resistance, fast nickel plating, layer thickness up to 10-50, um, and no defects such as peeling and nickel bubbles after hydrogen burning.
The disadvantages of chemical nickel plating are
① the layer is an amorphous lamellar structure. However, after heat treatment, the layer crystallizes, and its lamellar structure gradually disappears, but the tensile strength of ceramic metal sealing parts is reduced.
② High cost of plating solution, short life span, and high energy consumption.
③The plating solution is sensitive to impurities and requires frequent treatment, thus making the operability of the process relatively complicated
Facts Why You Should Nickel Plate Your Aluminum Parts
Aluminum has many excellent properties that make it an ideal choice for manufacturing.
Nickel plating can significantly improve the performance of aluminum parts.
Some of the compelling benefits of nickel-plated aluminum parts are as follows:
① It improves corrosion resistance.
② Gives your parts an aesthetic appearance.
③ Significantly improves wear resistance.
④ Has excellent hardness.
⑤ It can be used as a base layer for other types of finishes.
We offer a complete chain of services for aluminum die casting parts from design to final finish. Nickel plating is just one of the various finishes we offer. Contact us if you have any other needs for your aluminum die casting project.