glossary
Abrasion
Abrasion is material removal and occurs in tribological contacts when the mating body is considerably harder and rougher harder and rougher than the tribologically stressed base body or when hard particles are pressed into a tribologically stressed material. During a relative movement of the two friction partners, abrasive wear can occur from the softer base body due to various material separation processes (plowing, chipping, fatigue, breaking).
Abrasion resistance
Abrasion resistance is the resistance of a surface to abrasion. Abrasion is the loss of material on the surface caused by the application, which is caused by mechanical stress (friction). In materials science, abrasion is considered wear.
Adhesion
Adhesion describes the property of a surface layer to form a permanent bond with a base material. The adhesion is based on various mechanisms of physical-chemical bonding forces and mechanical interlocking. To achieve good adhesion, a coordinated pre-treatment (cleaning, degreasing) of the base material is necessary. When selecting the coating material, the thermal expansion coefficient in comparison to that of the base material must be taken into account, as otherwise the adhesion will be reduced when the temperature changes with the formation of shear forces.
Anode
The anode is the electron-accepting electrode (positive pole) in a galvanic cell. The anions migrate to the anode and are discharged there. If necessary, anodization of the electrode material can take place, which is the principle of anodization (see anodizing).
Anodic degreasing
Anodic degreasing is a specific process step in degreasing (see degreasing), whereby the workpiece is connected as an anode. In alkaline electrolytes, oxygen is subsequently formed on the workpiece, which electrolytically dissolves metallic impurities and also the surfaces of the base material.
Anodic dip coating
Anodic dip coating is a special type of electrocoating in which the workpiece to be coated is connected as an anode. In electrocoating, paint deposition on the workpiece is triggered by chemical reactions (coagulation) of the binder. For coating, a voltage is applied between the two electrodes, which supplies the current flow required for paint deposition and coagulation.
Anodic oxidation
Anodic oxidation generally describes the oxidation at the anode of an electron pair. Electrons are released at the boundary layer to the electrolyte, which oxidizes the anode material (see anodizing).
Anodizing
Anodizing is the process of creating an oxide coating on light metals through anodic oxidation. The top layer is used to improve corrosion and wear protection or for decorative purposes. In this process, known as anodizing, oxide layers of usually 5 to 40 µm thickness are produced on aluminium, for example. Anodic layers can also be colored very well for optical purposes.
Breakdown voltage
In electrical engineering, breakdown voltage refers to the voltage that must be exceeded for a voltage breakdown to occur through a material (e.g. insulator). If a breakdown voltage is related to the thickness of an insulating material (usually kV/mm), this is referred to as dielectric strength. The breakdown voltage can be tested, for example, for anodic layers in accordance with DIN EN ISO 2376. The breakdown voltage depends on the thickness of the anodically produced oxide layer as well as on several other factors, in particular the composition of the base material, its surface quality, the quality of the compaction, the dryness of the sample and the degree of ageing.
Cascade rinsing
Cascade rinsing is a rinsing process in which the water in a multi-part tank flows from one segment to the next. The components to be rinsed are moved in the opposite direction from the last segment to the first and thus come into contact with water of increasing cleanliness one after the other.
Cathode
A cathode is an electrode through which electrons are supplied to a component via an electrical conductor. These electrons are transferred to the chemical reaction partners (electrolyte) at the phase boundary, the so-called reduction reaction.
Chemical resistance
Chemical resistance refers to the resistance of a coating or a metallic coating to acids, alkalis, solvents and cleaning agents or other chemical solutions. So-called resistance lists are often used for evaluation, although the informative value of such lists is limited and usually does not reflect the stresses relevant in practice.
Coating thickness measurement
The layer thickness is a key quality feature of a coating or metallic coating. It has a significant influence on the durability and therefore the functional properties required by the customer (corrosion resistance, wear resistance, electrical properties, appearance, etc.). In coating thickness testing, the choice of measurement method to be used depends primarily on the substrate and coating material. Non-destructive measurements can be carried out, for example, by means of measuring probes using eddy current and magnetic methods. In addition, verification can be carried out using metallographic microsection and microscopic methods and combined with a hardness measurement, for example.
Contact corrosion
Contact corrosion, also known as bimetallic corrosion or galvanic corrosion, is the electrochemical corrosion of two different metallic materials or electron-conducting compositions that have a different position in the electrochemical voltage series. This results in different corrosion resistance when the two partners are in direct contact and are wetted together by an aqueous electrolyte (galvanic corrosion element), causing the less noble material partner to corrode more quickly (sacrificial anode).
Conversion layers
Conversion layers are created by an (electro)-chemical reaction (conversion layer) with a treatment solution. This results in the formation of a covering layer (conversion layer) consisting of elements of the base material and the attacking agent. Examples of such processes are passivation, phosphating or anodizing.
Corrosion
Corrosion is the “physico-chemical interaction between a metal and its environment which leads to a change in the properties of the metal and which can lead to significant impairment of the function of the metal, the environment or the technical system of which they form a part” (DIN EN ISO 8044). Corrosion therefore leads to a measurable change in the material, the so-called corrosion phenomenon. If the function of the component/system is impaired as a result, this is referred to as corrosion damage.
Corrosion protection
Corrosion protection describes measures within the corrosion system to prevent or reduce corrosion damage.
Corrosion resistance
Corrosion resistance describes the “ability of a metal to maintain its functionality in a given corrosion system” (DIN EN ISO 8044).
Corrosion testing
Corrosion testing is the testing of materials in specified, usually non-practical media to check the delivery quality or the required condition.
cross-cut test
A cross-cut test can be carried out to assess adhesion to coated surfaces. In this empirical test, six parallel cuts are applied to a coated substrate up to the base material and then crossed by six cuts, also at right angles. The distance between the individual layers must be the same and depends on the layer thickness and the hardness of the base material.
Decoating
Decoating is the removal of coatings that have already been applied in a defined manner. The processes that can be used for decoating are, for example, blasting processes, machining processes or chemical processes, depending on the coating material to be removed and the base material. Decoating is defined as a cleaning objective in DIN 8592.
Degreasing
Degreasing is the cleaning of metal surfaces to remove organic components. The processes and the degreasing solutions used are adapted to the type and intensity of the soiling and the metal to be degreased. A distinction can be made between e.g. boiling degreasing (soak cleaning), pickling degreasing, electrolytic degreasing, emulsion degreasing, cold degreasing or solvent degreasing. The cleaning effect can be further enhanced by using ultrasound. Degreasing is a necessary requirement for the subsequent removal (pickling) of oxide layers, as otherwise the pickling agents used cannot work on correspondingly contaminated surface areas.
Demineralized water
Demineralized water is also known as deionized water (deionate), in which the salts (anions and cations) usually found in normal tap water are largely filtered out. This is done either using special ion exchanger cartridges or by reverse osmosis with downstream residual desalination. The degree of purity of the demineralized water is determined by the electrical conductivity (Siemens per metre – S/m). Ion exchange usually achieves conductivities of less than 5 µS/cm.
Deoxidation
Deoxidation (a kind of pickling) is an intermediate treatment stage for removing thin films of oxides and other passive layers that can form between individual process stages and which can impair the adhesive strength of subsequently applied coatings. Deoxidation produces a metallically pure surface on which electrocrystallization can take place in the desired form. Acidic solutions are generally used for deoxidation.
Deposition
Deposition is the electrolytic production of a metallic coating. The layer thickness produced during electrolytic metal deposition is determined in micrometers (µm) or metal quantity per area (g/cm² or g/m²). When considered per unit of time, the deposition rate can be defined from this, which depends on the current density and the current yield, among other things, depending on the process.
Dispersion deposition
Dispersion deposition is a metal deposition process in which additional solid particles are incorporated into the coating. By co-depositing such dispersion particles, certain coating properties can be specifically modified and optimized. In this way, for example, the hardness and wear resistance of Ni/P coatings for special applications can be influenced by incorporating hard materials (e.g. silicon carbide) or the sliding properties by incorporating dry lubricant (e.g. PTFE).
Ductility
Ductility is the property of a material to deform permanently under the influence of an external force before breaking. If metals deform flexibly, they are called ductile. If they deform very little and are fragile, they are called brittle. The degree of ductility can be expressed by the elongation at break A. For ceramics and hard materials, A is ≤ 0.1%; for ductile materials, the value for A is around 10%.
Electrical conductivity
Electrical conductivity is a material property and indicates how well electrical current is conducted. Electrical conductivity is preferably achieved without changing the material by transporting electrons. Depending on the conductivity, a distinction is made between superconductors, conductors (especially metals), semiconductors (e.g. silicon) and non-conductors (non-metals, organic compounds). The electrical conductivity is given in Siemens (S) per meter.
Electroless metal deposition
Electroless metal deposition is a metal deposition process in which the respective metal ions are reduced by ion exchange or by means of special chemical reagents. An external power source is therefore not required. Other terms for this process are chemical, autocatalytic or chemical-reductive. One example of electroless metal deposition is nickel-phosphorus coatings (electroless nickel). The Ni/P layers are deposited autocatalytically from aqueous electrolytes. In addition to nickel salt as a supplier of nickel ions, the electrolytes also contain a suitable reducing agent, which serves as a supplier of electrons and the alloying element phosphorus. The electrons released by the reducing agent discharge the positively charged nickel ions, which then deposit together with the phosphorus on the catalytic substrate to be coated and form the Ni/P layer. Other electrolyte components (additives) such as complexing agents, stabilizers, accelerators and buffer substances are required to ensure a perfect deposition process and optimum coating properties.
Electrolyte
Electrolyte refers to a chemical compound that usually contains ions in a liquid state and which moves in a directed manner under the influence of an electric field. The electrical conductivity of such ion-conducting liquids is lower than that of metals. An important application of electrolytes is in electroplating (galvanic cells). Electrolytes are usually aqueous solutions of acids, bases and special additives.
Electrolytic degreasing
Electrolytic degreasing is a process for degreasing metallic surfaces before electroplating. The metal is connected as an anode or cathode and alkalis are used as a cleaning medium with the addition of surfactants and, if necessary, complexing agents.
Electroplating
Electroplating is a surface technology process for the electrochemical deposition of metals on metallic or metallized surfaces using an electrolyte and direct current. The base material is used as the cathode. The metal ions required for layer formation are already contained in the electroplating bath and are added during the process either by dissolving the anode or (in the case of insoluble anodes) by adding new metal salt. Depending on the process, the bath temperature is usually between 20 and 90 °C and the current density can range from 0.1 to 1000 A/dm². The galvanic metal coating is usually used for corrosion protection or to improve wear resistance.
Film contamination
Film contamination can impair subsequent production processes such as bonding, welding or coating of component surfaces. The residues are, for example, media from production, such as oils, greases, cooling lubricants or cleaning agents. In most cases, the filmic contaminants are distributed inhomogeneously on the component and are usually more pronounced on edges and surface structures. One possible method of detecting film contamination is visual inspection, which can be supported with white or UV light if necessary. However, there must already be considerable contamination. Other methods include wettability tests with test inks, test pens or water aerosol. Fluorescence testing or contact angle measurement can also reveal certain filmic contamination. For a quantified measurement, a quantitative chemical analysis of the detached residues from the component or a vacuum test using residual gas analysis of the entire workpiece surface is necessary.
Hardness
Hardness is the mechanical resistance that a material offers to the mechanical penetration of another body. A distinction is made between different types of hardness depending on the type of impact. For example, hardness is not only the resistance to harder bodies, but also to softer and equally hard bodies. The definition of hardness differs from that of strength, which is the resistance of a material to deformation and separation. In the common static test methods (according to Brinell, Knoop, Rockwell or Vickers), an indenter is pressed into the material or coating material with a defined force. The hardness value is then calculated from the size of the resulting indentation.
High-speed anodizing
High-speed anodizing is a special type of selective anodizing of aluminium materials under very high current densities and the associated shorter process times. The high current density and consequently high heat development requires a sophisticated component holder (tool) and cooling. The latter is achieved by high circulation of the coating electrolyte during the process.
Hull cell
The Hull cell is a standardized small-scale electroplating unit for the laboratory and has long been a standard method in electroplating technology. It consists of a trapezoidal container made of electrically non-conductive material for arranging the electrodes. These are arranged in such a way that the cathodic and anodic effects (field line influence) can be observed over wide current density ranges. In this way, the influences of the bath parameters (e.g. temperature, pH value, electrolyte composition, etc.) on the properties and quality of the deposited layer can be determined as a function of the current density.
Hydrogen embrittlement
The interaction of hydrogen with metallic materials can have an adverse effect on material properties and behavior. The effect of hydrogen absorption (absorbable atomic hydrogen) and the phenomenon of hydrogen embrittlement manifests itself, for example, in losses of mechanical properties, processability, deformability, toughness and fatigue strength. The risk of this hydrogen-induced component damage is present in many areas of technology, including the deposition of metal coatings and their pre-treatment processes or later in the application due to corrosion processes.
Impedance spectroscopy
Impedance spectroscopy is the determination of the alternating current resistance (impedance) as a function of the frequency of the alternating current. For this purpose, the frequency is varied over a defined frequency range at a constant alternating voltage, the corresponding alternating current is recorded and the impedance is calculated from this. A major area of application is electrochemistry, where impedance spectroscopy is used to investigate the corrosion behavior or corrosion protection of coatings. The advantages are quantitative statements in direct comparison as well as quick and simple implementation (short-term corrosion investigation).
Intergranular corrosion
Intergranular corrosion is a special form of corrosion in which the corrosion runs along the grain boundaries. The reasons for this lie in the different compositions between the grain and grain boundary and the resulting differences in corrosion resistance. As a result, the grain boundary is more susceptible to corrosion in comparison and is preferentially dissolved. Examples of susceptible materials are austenitic steels (formation of chromium carbides) or aluminum alloys of series 2 and 5.
Laser beam oxidation
This process is a selective treatment of the component surface in which an oxidation layer is created using a laser. A layer with high hardness and wear resistance is created in localized and very precise, easily accessible surface areas. By using a process gas and applying heat with the laser, the area near the surface of the substrate is melted and converted into an oxidation layer. The process takes place entirely without liquid chemicals or electrolytes. The process can be used on aluminum and titanium materials.
Masking
Masking refers to the process of covering in electroplating. For this purpose, the surface area that is not to be coated is covered with the help of cover varnishes, foils or adhesive tapes in order to protect these areas from the ingress of coating material.
Metallography
Metallography is the visualization and qualitative and quantitative description of the structure of metallic materials. For this purpose, it is necessary to separate out the section to be examined beforehand and then prepare it in an embedding compound as well as high-gloss polishing. Depending on the material, special etchings are necessary to visualize the microstructure (grain size, grain boundaries, orientation, precipitation, etc.).
Passivity
Passivity describes the property of certain metals or alloys to form a thin oxide layer through interaction with the environment (atmosphere), which significantly improves corrosion resistance. Examples of such metals are chromium, aluminum, nickel, tin or titanium. A passive layer can also be produced by a defined technical process, e.g. by anodizing aluminium.
Phosphating
Phosphating describes a process in surface technology for creating a conversion layer of metal phosphates. A chemical reaction of the surface with the surrounding electrolyte results in the formation of this firmly adhering conversion layer consisting of elements of the base material and the components of the phosphating solution. The layer created improves the temporary corrosion protection as well as the adhesion of subsequent paint layers and their corrosive infiltration. Common materials for phosphating are iron, zinc and their alloys, but aluminum can also be treated in special solutions.
Pickling
Pickling is the removal of predominantly oxidic deposits (inorganic impurities, rust, scale) from metal surfaces using chemical substances to produce a clean and bright metal surface. Depending on the base material to be pickled, various acids (hydrochloric, sulphuric, phosphoric, nitric or hydrofluoric acid) or mixtures thereof or alkalis are used as pickling agents. Pickling-accelerating substances or pickling inhibitors can also be added to the solutions. In electrolytic pickling, which is also common, the pickling effect is influenced by applying a current. This can be done either anodically, cathodically or with alternating current. The metal surface must be degreased before the actual pickling process, as the acids primarily used as pickling agents cannot act on greased areas. As a by-product of pickling steel materials, for example, the hydrogen formed can diffuse into the metal and possibly impair the properties of the base material (hydrogen embrittlement).
Plasma electrolytic oxidation (PEO)
This process can be used to produce oxidic layers on the light metals aluminum, magnesium and titanium as well as their alloys. The origins of the process date back to the 1980s, when it was also known as “anodic oxidation by spark discharge (ANOF)”. These layers are produced in aqueous electrolytes by applying a special external current source under spark discharge. The component is connected as an anode and corrosion and wear-protective layers are formed. Special electrolyte components can also be used to produce black layers, which can also be used in optical applications with low required reflection values due to the layer structure.
Product carrier
The product carrier is the device in which the workpieces/components are suspended or positioned during the surface treatment process. The design and material of the product carrier varies depending on the geometry and number of workpieces as well as the specific process.
Rectifiers
Rectifiers are electrical devices that convert alternating or three-phase current into direct current and are used to produce metallic coatings or anodized layers in electroplating.
Release agent
Substances used in technology to keep adjacent materials separable even at high temperatures and pressures. One application is, for example, preventing cast or molded parts from sticking to the mold during molding processes (mold release agents). Residues of such release agents usually have a detrimental effect during further processing (see film contamination).
Residual dirt
Residual dirt refers to the impurities that are still on the component after industrial telescopic cleaning and are technically unavoidable. Small amounts of residual dirt do not have to impair the function of the finished components and are therefore perfectly tolerable, which is why technical cleanliness is then fulfilled. The cleanliness requirements vary depending on the application, whereby sensitive systems such as in medical technology or electronics have higher cleanliness requirements. However, the necessary cleanliness measures should also be considered from an economic perspective, as the costs and effort involved increase considerably with the requirements.
Residual stress
Residual stresses are mechanical tensile and compressive stresses that prevail in a body that is not subject to external forces and is in thermal equilibrium. Residual stresses can be caused by plastic deformation, inhomogeneous material structures, thermal influences or metallic coatings. Residual stresses can be divided into three different types. Residual stresses of the first type are those that occur in the macroscopic range, residual stresses of the second type affect several crystals and residual stresses of the third type occur within a crystal at only a few atomic distances.
Roughness
Roughness describes the unevenness of a surface. There are various calculation methods for the quantitative assessment of these different surface heights, the results of which describe various surface characteristics in the form of roughness parameters.
Salt spray test
This is a widely used corrosion test to verify the delivered quality of components (DIN EN ISO 9227). For coated components, the quality of the coating or the metallic coating can be tested in this way. The test is carried out, for example – with a neutral test medium – by nebulizing a sodium chloride solution (50 g/l) at 35 °C in a test chamber. There are also more stringent variants with the addition of acetic acid or copper(II) chloride dihydrate. The quality characteristic is a predefined period of time until a certain component/surface condition occurs. This condition can be determined, for example, by evaluating the degree of protection (DIN EN ISO 10289).
Sandblasting
Sandblasting is compressed air blasting with solid abrasive for the surface treatment of a workpiece (blasting material). The material treatment is used to remove unwanted components from the surface, such as impurities, rust, paint, or for targeted roughening, matting or densification. Sand, corundum, glass, plastic and others can be used as blasting media, which then produces a mostly abrasive effect on the blasting material by accelerating it with compressed air.
Scanning electron microscopy
Scanning electron microscopy describes a process for imaging objects and surfaces using electron beams. The scanning electron microscope (SEM) consists of a vacuum chamber for inserting the component to be examined, an electron source, a high-voltage source and various lenses, deflection units and detectors. The electron beam scans the surface for imaging and the resulting secondary electrons are used for image processing with the aid of the detector. The resolution depends on the device equipment and can provide good results in the range down to less than 10 nm. The material contrast can also be influenced by the backscattering of electrons. The SEM is often complemented by a qualitative-quantitative analysis method for identifying chemical elements in the upper layers, known as energy-dispersive X-ray spectroscopy (EDX). The sample is bombarded with a focused electron beam with a defined energy and the characteristic X-rays generated for the elements present are recorded by a detector. This not only analyzes the immediate surface area, but also detects deeper areas due to the penetration of the electron beam. The method can be used to determine all elements from boron upwards.
Sealing
Sealing refers to the post-treatment of anodic coatings to significantly improve corrosion resistance. Post-treatment is usually carried out with hot water (96-100 °C) and serves to close the pores. There are other variants with the addition of nickel or chromium, for example, and the anodic layers can also be colored before post-treatment (reference HC).
Selective anodizing
In this process, the aluminium components to be anodized are placed in special tool holders and the areas to be coated are separated using special sealing technology. The electrolyte then enters under flow and the coating is formed after the current is applied. This process usually takes place within a minute and layer thicknesses of up to 25 µm can be achieved. Electrolyte consumption is kept to a minimum and, in addition to cost-effectiveness, the encapsulated process also ensures a high level of work and process safety (reference SELGA-COAT).
Soak cleaning
Soak cleaning (also known as hot degreasing or alkaline cleaning) is a pre-treatment with diluted solutions of alkali hydroxide, alkali carbonate, alkali phosphate, alkali borate or alkali silicate as well as wetting and emulsifying agents. Depending on the required cleaning performance and condition of the components (soiling), boil-off degreasing is carried out at an elevated temperature (> 55 °C) and dwell times of 2 – 10 minutes.
Stylus method
The stylus method is a measuring method for the two-dimensional measurement of a surface. A stylus system (needle) is moved horizontally over the surface under a feed motion and the resulting movements of the needle are recorded in a vertical direction (DIN EN ISO 3274). In further steps, roughness parameters can be formed from the measurement results (DIN EN ISO 4287).
Substrate
The substrate is the workpiece or component that serves as a base for the coating material to be applied.
Surface tension
Surface tension is the force acting at the interface of liquids and is based on the mutual attraction of the liquid molecules. The liquid forms the smallest possible surface area and without the effect of an external force, a spherical shape is created. A high surface tension of water, for example, often has a negative effect in the production of metallic coatings, and wetting agents are added to reduce the surface tension.
Taber abraser
This type of test involves a frictional load with subsequent determination of the coating mass loss (ISO 10074, ASTM D4060). The frictional load is applied in rotation via pressed-on friction rollers. The lower the loss of mass after a defined running time, the higher the abrasion resistance of the coating material.
Tampon electroplating
Tampon electroplating is an electroplating process in which the workpiece to be coated is not immersed in an electrolyte, but is wetted with a pad (brush, paintbrush) connected as an anode. The tampon and the electrolyte contained in it are moved back and forth several times over the area to be coated, which realizes a local layer application.
Tarnishing
Tarnishing refers to the phenomena on metal surfaces caused by interaction with the atmosphere. These very thin, firmly adhering layers (metal oxides, carbonates, sulphides, etc.) lead to an altered optical appearance due to interference. Examples include the tarnishing of silver when exposed to sulphur-containing substances (protein), whereby black sulphidic tarnishing layers are formed. Or the discoloration of electroless nickel layers due to a heat source in the atmosphere.
Technical cleanliness
Technical cleanliness refers to the sufficiently low contamination of workpieces with particles, depending on the requirements. The maximum permitted number of particles per unit area is specified; a distinction is also made between metallic and non-metallic particles where applicable.
Thermal conductivity
Thermal conductivity is a physical quantity that indicates how well a material can conduct heat. It describes the ability of a material to transport thermal energy through its structure and particle movements. Thermal conductivity is measured in watts per meter and Kelvin (W/mK). Materials with high thermal conductivity can transport heat quickly and efficiently, while materials with low thermal conductivity can only transport heat slowly or not at all. Metals such as copper and aluminum have a high thermal conductivity and are therefore often used in heat transfer, e.g. in radiators or heat sinks. Insulating materials such as polystyrene or glass wool, on the other hand, have low thermal conductivity and are therefore used as thermal insulation.
Ultrasonic cleaning
This involves cleaning with mechanical support from ultrasonic waves introduced into the immersion tank. The ultrasonic waves in the aqueous cleaning solution create certain pressure conditions (tensile and compressive stresses), which fall below the vapor pressure of the cleaning solution in low-pressure areas and lead to the formation of cavitation bubbles. The subsequent increase in pressure causes these bubbles to collapse again and a microjet is formed, which can generate a mechanical cleaning effect on the surface and thus support the cleaning effect.
Vibratory finishing
Vibratory finishing is one of the machining production processes for surface treatment of mostly metallic workpieces. The components are ground as bulk material in a container using special abrasive media and usually an aqueous additive (compound). An oscillating or rotating movement of the work container creates a relative movement between the component and the abrasive media, which causes the desired material removal, particularly on the edges. The process is used for deburring, edge rounding, coarse and fine grinding, cleaning, brightening, smoothing, shining, polishing, descaling or derusting.
Wetting
Wetting describes the behavior of liquids on contact with the surface of solids. The corresponding property of the surface of the solid is the so-called wettability. Depending on the type of liquid, material and surface properties (roughness, contamination, interface), the wetting behavior varies. It is important for the wetting of a surface that the surface energy is higher than the interfacial energy of the liquid. To improve wettability, various pre-treatment measures can be carried out on the surface, such as mechanical processes, pickling, degreasing or plasma activation.
Whisker
Whiskers are usually spontaneously growing hairpin crystals caused by compressive stress in galvanic layers of deep melting metals (e.g. tin). Due to their length of up to several millimeters, they pose a serious problem for the reliability of electronic components, especially in the case of tin whiskers.
Zincate treatment
The purpose of zincate treatment is to prevent the aluminum surface from reacting with air in order to enable subsequent metallic coatings to adhere firmly. Since aluminum and its alloys have a high affinity for oxygen, they typically form a cohesive oxide layer very quickly in air or water, which prevents metallic bonding of deposited layers. An adhesive bond can only be achieved if a temporary protective layer is applied at the same time after the oxide skin has been removed. The zincate process, in which zinc – and possibly alloying elements – is deposited in a strongly alkaline solution (zincate pickle) by cementation on the dissolving aluminum surface (in the range up to 500 nm), is state of the art.