SPI
Special Processes Institute
sp-i.org
Electroplating Science Knowledge Guide
Electroplating Science Knowledge App
Explore the science that connects electricity, electrochemistry, bath composition, surface preparation, current distribution, part geometry and process control to deposit thickness, adhesion, appearance, corrosion performance and functional reliability.
Mobile-first learning Interactive calculations Design and process insight
I × t
Charge controls theoretical deposited mass
A/dm²
Current density controls local deposition behaviour
18+
Deposit metals and alloy systems compared
0%
Best knowledge-test score
The Electroplating Cell
Direct currentWhat happens at each electrode?
Cathode: reduction and metal deposition
The part is normally connected to the negative output. Positively charged metal species reach the cathode surface, receive electrons and become metal atoms. Competing reactions—especially hydrogen evolution—consume current and reduce cathode current efficiency.
Anode: oxidation and current supply
A soluble anode can dissolve to replenish metal ions. An insoluble anode conducts current but does not supply the principal deposit metal; oxidation of water or other species occurs, so bath chemistry must be replenished separately.
Electrolyte: more than “conductive water”
The electrolyte provides metal species, ionic conductivity, buffering, complexing, anode behaviour and controlled mass transport. Additives modify nucleation, grain structure, levelling, brightness, stress and wetting.
Core principle: electrical charge sets the theoretical amount of reaction, while local current density, chemistry, mass transport and efficiency determine where and how well the metal is deposited.
Common cathode and anode reactions
| System | Cathode reaction | Anode reaction | Important competing behaviour |
|---|---|---|---|
| Copper from Cu²⁺ | Cu²⁺ + 2e⁻ → Cu | Cu → Cu²⁺ + 2e⁻ (soluble copper) | Hydrogen evolution at low metal activity or excessive polarisation |
| Nickel from Ni²⁺ | Ni²⁺ + 2e⁻ → Ni | Ni → Ni²⁺ + 2e⁻ | Hydrogen evolution; local cathode pH rise; possible hydroxide formation |
| Zinc from Zn²⁺ | Zn²⁺ + 2e⁻ → Zn | Zn → Zn²⁺ + 2e⁻ or oxygen at inert anode | Hydrogen co-evolution depends strongly on bath type and substrate |
| Silver from Ag⁺ complex | Ag-complex + e⁻ → Ag + released ligand | Ag → Ag⁺ + e⁻ or inert-anode oxidation | Complexation controls free Ag⁺ activity and deposit distribution |
| Hard chromium from Cr(VI) | Multi-step reduction to Cr metal | Oxygen evolution at lead-alloy/inert anodes | Very substantial hydrogen evolution; low current efficiency |
| Gold from Au(I) complex | Au-complex + e⁻ → Au + ligand | Typically inert anode oxidation | Additive and complexant control are critical; free-metal activity is low |
Current, Voltage and Resistance
V = I × R and I = V / R
Voltage is the electrical potential needed to drive the required current through busbars, contacts, solution, films and electrode polarisation. Current is the rate of charge flow. The rectifier may be controlled by current, voltage, waveform or a programmed profile.
Do not specify volts as a substitute for current density. The same voltage can produce different current after changes in bath conductivity, temperature, electrode spacing, load area, contact resistance or anode condition.
Interactive Electrical Relationship
Current Density (CD)
Local and average values differAverage cathode CD = total current / total plated cathode area
Common units are A/dm², A/ft² (ASF) and A/m². Current density is more useful than total current because it relates electrical load to plated area. However, average CD hides local peaks and lows created by geometry and field distribution.
Example: 180 A applied to 60 dm² gives an average cathode current density of 3 A/dm². A sharp corner may experience much more; a deep recess much less.
Too Low Current Density
- Slow deposition and poor productivity.
- Deposit may be dull, coarse, porous or outside the additive operating window.
- Alloy composition may shift.
- Low-CD areas may fail to cover, especially recesses.
- Extended exposure can increase contamination or attack of the basis metal in some baths.
- Some impurities preferentially deposit at low CD.
Too High Current Density
- Burning, powdery or tree-like deposits.
- Excessive hydrogen evolution and pitting.
- Metal-ion depletion at the cathode diffusion layer.
- Roughness, high stress, cracking or poor adhesion.
- Brightener depletion and local chemistry changes.
- Excessive edge/corner build and dimensional loss.
Cathode Current Efficiency (CCE)
CCE (%) = current used for metal deposition / total cathode current × 100
CCE accounts for competing cathodic reactions. At 100% efficiency all cathodic charge deposits the target metal. At 80%, only 80% contributes to the calculated metal mass; the rest drives reactions such as hydrogen evolution or reduction of other species.
High CCE
Faster metal deposition for a given charge and generally less hydrogen generation.
Faster metal deposition for a given charge and generally less hydrogen generation.
Low CCE
More gas, lower deposition rate, greater energy use and potentially more hydrogen-related risk.
More gas, lower deposition rate, greater energy use and potentially more hydrogen-related risk.
Variable CCE
Efficiency can change with CD, composition, temperature, agitation, contamination and deposit alloy ratio.
Efficiency can change with CD, composition, temperature, agitation, contamination and deposit alloy ratio.
Why Valency Matters
Faraday deposition depends on the number of electrons required per metal atom. The equivalent mass is atomic mass divided by valency. For the same charge and 100% efficiency, a monovalent ion deposits more mass than the same metal would from a divalent ion because fewer electrons are required per atom.
| Species | Typical valency used in calculation | Electrons per atom | Significance |
|---|---|---|---|
| Ag⁺, Au⁺ | 1 | 1 | High electrochemical equivalent mass; one Faraday deposits one mole of metal. |
| Cu²⁺, Ni²⁺, Zn²⁺, Sn²⁺ | 2 | 2 | Two Faradays are required per mole deposited. |
| Cr³⁺ | 3 | 3 | Three electron equivalents per mole in the simplified metal reduction balance. |
| Cr(VI) bath to Cr metal | 6 electron change overall | 6 | Low efficiency and complex intermediate chemistry make practical deposition very different from simple divalent plating. |
Part Geometry and Current Distribution
Average CD is not local CDEdges and Points
Electric field lines concentrate at sharp radii, projecting edges and points. This raises local CD, causing excessive thickness, burning, roughness or nodules.
Recesses and Shadows
Deep pockets, concave surfaces and shielded regions receive less current and poorer solution renewal, producing thin or absent deposit.
Orientation
Gas release, drainage, anode view, rack position and agitation direction influence pitting, streaking, thickness distribution and contamination traps.
Throwing Power and Microthrowing
Throwing power describes the ability of a plating system to produce a more uniform deposit over areas with different primary current distribution. It depends on bath conductivity, polarisation behaviour, metal-ion transport, additives, electrode spacing and geometry. Microthrowing concerns distribution into very small surface irregularities or microfeatures and can differ from macrothrowing.
Factors that often improve distribution
- Appropriate complexing and polarisation.
- Higher solution conductivity.
- Correct anode placement and shielding.
- Auxiliary anodes in recesses.
- Robbers/thieves near high-CD edges.
- Pulse or pulse-reverse waveforms where validated.
Do not confuse throwing power with levelling
Throwing power deals mainly with thickness distribution over geometry. Levelling is the tendency to preferentially fill microscopic valleys and smooth the surface profile, commonly influenced by organic additives and local mass transport.
Throwing power deals mainly with thickness distribution over geometry. Levelling is the tendency to preferentially fill microscopic valleys and smooth the surface profile, commonly influenced by organic additives and local mass transport.
Blind Holes
- Electrical field penetration is weak as depth-to-diameter ratio increases.
- Hydrogen or air can become trapped and exclude solution.
- Agitation and solution exchange inside the hole are poor.
- Cleaning and rinsing residues are difficult to remove.
- Post-treatment solutions may remain trapped and bleed out later.
- Specify whether full coverage, minimum local thickness or only corrosion protection at the entrance is realistic.
Design warning: deep blind holes should not be assumed to receive the same deposit as exposed surfaces. Through-holes, venting, drainage, auxiliary anodes or an alternative process may be needed.
Enclosures and Faying Surfaces
- Closed seams and overlapping joints trap cleaners, acids and plating solution.
- Electrolyte may penetrate by capillary action but not rinse out.
- Corrosive bleed-out can occur in service.
- Electrical contact between assembled faces may create unintended plating bridges or uncoated shielded areas.
- Hydrogen and gas pockets can form.
- Plate components before assembly where practical, or provide sealing, vents, drains and explicit coverage requirements.
Design for Electroplating
| Design feature | Plating risk | Preferred design response |
|---|---|---|
| Sharp external edge | High CD, thick/burnt deposit | Use practical radii; allow for local thickness; use shielding/robbers. |
| Deep recess | Thin deposit and poor cleaning | Reduce aspect ratio; open geometry; auxiliary anode or validated alternative. |
| Blind cavity | Air/gas lock and chemical entrapment | Vent and drain; orient for fill/drain; define realistic coverage. |
| Close-tolerance fit | Deposit reduces clearance | State dimensions before/after plate; provide machining allowance or mask. |
| Thread | Pitch diameter changes, bridging, gauge failure | Specify after-plate class or pre-plate allowance; define masking. |
| Faying surface | Entrapment and incomplete coverage | Plate before assembly or seal/vent; avoid capillary seams. |
| Rack contact area | Unplated mark or local burning | Define permissible contact location and cosmetic/functional limits. |
| High-strength steel | Hydrogen embrittlement risk | Control cleaning/plating route and baking; consider alternative coatings. |
What a Plating Bath Contains
Each component has a purposeMetal sourceSupplies deposit metal ions or complexes.
Conducting saltRaises conductivity and reduces required voltage.
ComplexantControls free-metal activity, anode behaviour and distribution.
Buffer / pH controlResists harmful local and bulk pH change.
Anode activatorSupports dissolution and prevents passivation where relevant.
Wetter / surfactantReduces surface tension and helps release gas bubbles.
Brightener / grain refinerChanges nucleation and crystal growth to produce fine, bright deposits.
Carrier / suppressorProvides background polarisation and controls additive response.
LevellerAdsorbs preferentially at peaks/high-mass-transfer areas to smooth microtopography.
Stress reducerModifies internal stress and deposit mechanical behaviour.
Alloy controllerHelps maintain desired co-deposition ratio.
WaterSolvent and transport medium; purity strongly affects reliability.
Acid Baths
Acidic plating solutions often have high conductivity, high metal-ion activity and strong high-current-density performance. Examples include acid copper, sulphamate/sulphate nickel, acid zinc, tin and some gold systems.
- Often require excellent activation immediately before plating.
- Can attack susceptible substrates if entry current or transfer is poor.
- May have weaker macrothrowing than strongly complexed alkaline systems.
- Local cathode pH may still rise due to hydrogen evolution.
Alkaline Baths
Alkaline baths frequently use complexants to keep metals soluble and reduce free-metal activity. Examples include alkaline zinc, copper strike systems and some tin, silver and gold chemistries.
- Can provide improved distribution and controlled deposition behaviour.
- May be more tolerant of certain substrate geometries.
- Complexant balance, carbonate build-up and contamination can be critical.
- Substrate attack and immersion deposition must still be controlled.
Typical Bath Chemistry Examples
| Bath family | Typical functional components | Characteristic behaviour | Key controls |
|---|---|---|---|
| Watts nickel | Nickel sulphate, nickel chloride, boric acid, wetters and organic additives | General-purpose nickel; chloride supports anode dissolution; boric acid helps buffer the cathode film | Ni, chloride, boric acid, pH, temperature, additives, impurities, filtration |
| Nickel sulphamate | Nickel sulphamate, activator/halide, boric acid and wetters | Used for low-stress engineering nickel and electroforming | Stress, sulphamate breakdown, pH, temperature, anode condition, organic contamination |
| Acid copper sulphate | Copper sulphate, sulphuric acid, chloride and organic additive package | High conductivity and bright/levelled deposits; chloride-additive balance is critical | Cu, acid, chloride, carrier, brightener, leveller, temperature, agitation |
| Alkaline non-cyanide zinc | Zinc oxide/metal source, sodium or potassium hydroxide, complexants and brighteners | Good distribution; alloy and appearance sensitive to caustic/zinc/additive ratio | Zinc, caustic, carbonate, additives, iron, temperature, anode/current balance |
| Acid chloride zinc | Zinc chloride, chloride conducting salts, boric acid or buffer and additives | High efficiency and brightness; often strong productivity | Zinc, total chloride, pH, additives, iron, temperature, filtration |
| Zinc-nickel alloy | Zinc and nickel sources, complexants/conducting salts and alloy-control additives | Composition is affected by CD, temperature, agitation and chemistry; anomalous co-deposition is common | Zn/Ni ratio, alloy %, pH, additives, contaminants, CD and temperature |
| Acid tin | Stannous salt, acid, antioxidant and organic additives | Solderable or functional tin; oxidation of Sn²⁺ to Sn⁴⁺ can create problems | Sn²⁺, acid, Sn⁴⁺, additives, sludge, temperature and agitation |
| Silver / gold complex baths | Metal complex, conducting salts, buffers and grain refiners/alloying species | Low free-metal activity supports controlled deposition; purity and contamination control are demanding | Metal, free complexant, density, pH, alloy %, metallic impurities and additive condition |
| Chromium(VI) | Chromic acid with catalyst species | Low CCE, high hydrogen evolution and poor throwing power; strict ratio and temperature control | CrO₃, catalyst ratio, trivalent chromium contamination, temperature, CD and anode condition |
| Trivalent chromium | Cr(III) complex, salts, buffers and proprietary additives | Different electrochemistry and colour/performance from Cr(VI); additive and contamination control important | Cr(III), complexant, pH, conductivity, contaminants, additives and anode system |
pH and the Cathode Film
Bulk pH is only part of the story. Hydrogen evolution consumes hydrogen ions or generates hydroxide near the cathode, so the local interfacial pH can be much higher than the measured tank pH. This may cause metal hydroxide formation, roughness, burning, porosity or additive changes.
- Buffers resist local pH movement.
- Agitation reduces concentration and pH gradients.
- pH electrode calibration and temperature compensation matter.
- Acid additions should be controlled and well mixed.
- Some baths are controlled by free acid/alkalinity rather than pH alone.
Addition Agents
Carriers / suppressors
Create broad cathodic polarisation, support fine grain and moderate deposition. Often consumed by electrolysis, drag-out and carbon treatment.
Brighteners
Promote fine-grained reflective deposits by affecting nucleation and crystal growth. Excess can increase stress, brittleness or poor ductility.
Levellers
Preferentially act at peaks or high-mass-transfer sites, suppressing local deposition so valleys catch up. Overuse can harm ductility or low-CD coverage.
Wetting agents
Lower surface tension so hydrogen bubbles detach more readily, reducing pits. Foam behaviour and compatibility with air agitation must be considered.
Surface Preparation: Adhesion Starts Before the Plating Tank
Atom-to-atom bonding requires a clean, active surfaceIdentify the basis material and condition
Steel grade, heat treatment, aluminium alloy, copper alloy, zinc die casting, stainless steel, nickel alloy, polymer and prior coatings require different routes.
Remove bulk soils
Solvent, aqueous, emulsion or ultrasonic cleaning removes machining oils, greases, polishing compounds and particulate.
Alkaline clean
Builders, surfactants and sequestrants emulsify/saponify soils. Electrocleaning can generate gas scrubbing but must suit the substrate and embrittlement risk.
Rinse thoroughly
Stops chemical carryover and prevents incompatible solutions contaminating the next stage.
Remove oxide / activate
Acid pickle, activation, deoxidising, desmutting or strike treatment removes passive films and establishes a surface that can initiate adherent deposition.
Enter plating without re-passivation
Minimise transfer time; maintain wet surfaces; use live entry or a strike where required by the substrate and bath.
Water-Break-Free Surface
A continuous sheet of water is a useful indication that gross hydrophobic soil is absent. It does not prove oxide removal, correct activation or microscopic cleanliness.
Cleaning Failure
Residual oil or polish causes skips, blisters, pits and peeling. Excessive attack can cause smut, dimensional loss, hydrogen charging or surface roughening.
Substrate-Specific Routes
Aluminium often needs etch/deoxidise/zincate or another bond layer. Stainless and nickel alloys need activation/strike control. Zinc die castings need gentle preparation and suitable strike layers.
Why Deionised Water Matters
- Reduces calcium/magnesium scale and insoluble salts.
- Limits chloride, sulphate and metallic contamination.
- Improves final rinse freedom from spots and residues.
- Supports reproducible bath make-up and analytical standards.
- Reduces uncontrolled ionic load in low-concentration or precious-metal baths.
DI water is not automatically clean water. Monitor resistivity/conductivity, microbial condition where relevant, storage/tank cleanliness and distribution-system contamination.
Rinsing Science
Rinsing removes the liquid film carried from one stage to the next. Drag-out volume depends on part area, orientation, withdrawal speed, viscosity, drainage time and trapped solution.
- Counterflow rinses improve water efficiency.
- Multiple stages reduce residual concentration geometrically.
- Spray rinses help exposed surfaces but may not exchange blind features.
- Agitated rinses improve diffusion from complex geometry.
- Conductivity or concentration monitoring can control rinse quality.
- Recovery rinses return valuable drag-out where compatible.
Agitation Methods and Functions
| Method | What it does | Advantages | Risks / limitations |
|---|---|---|---|
| Work movement | Moves cathode through solution and renews diffusion layer | Directly affects part; useful for racks and barrels | May be uneven across load; mechanical complexity |
| Air agitation | Rising bubbles circulate solution | Simple, good bulk mixing and heat transfer | Foam, airborne mist, oil contamination, not suitable for every additive system |
| Eductor agitation | Pumped jets entrain tank solution | Strong controlled flow without compressed air | Jet impingement can create local effects; requires filtration/pump control |
| Pumped circulation | Moves solution through filters, heaters and tank returns | Supports filtration, temperature and chemical uniformity | Poorly designed returns may create dead zones |
| Cathode rod movement | Reciprocates racks horizontally or vertically | Improves gas release and local transport | Contact reliability and mechanical wear |
| Barrel rotation | Tumbles small parts and renews contact/solution | Mass processing and surface renewal | Part damage, intermittent current, nesting and low local CD |
| Ultrasonic assistance | Cavitation enhances cleaning or local mass transfer | Useful for preparation and difficult recesses | Can damage delicate deposits/additives; scale-up and uniformity challenges |
Typical Electroplating Process Control
Control inputs, not just final thickness| Control family | Typical variables | Why it matters | Typical evidence |
|---|---|---|---|
| Product/load | Material, area, geometry, rack/barrel load, orientation, contact location | Determines current requirement, distribution and process route | Route card, load sheet, area calculation, setup standard |
| Electrical | Total current, average CD, voltage, ripple, ramp, waveform, ampere-hours | Controls deposition rate, efficiency, alloy ratio and defect risk | Rectifier display/log, shunt calibration, data logger |
| Bath composition | Metal, salts, acid/alkali, complexant, buffer, additives, breakdown products | Controls conductivity, metal activity, stress, appearance and distribution | Titration, instrumental analysis, Hull cell, supplier analysis |
| Physical | Temperature, agitation, filtration, level, density, flow | Controls kinetics, mass transfer, contamination and uniformity | Calibrated sensors, flow checks, filter records |
| Anodes | Area ratio, spacing, bags, corrosion, passivation, alloy, hooks | Controls current distribution, metal replenishment and particles | Anode inspection, mass balance, maintenance log |
| Preparation | Cleaner strength, time, temperature, current, acid activity, transfer time | Controls adhesion and basis-metal condition | Analysis, water-break test, process timer, operator checks |
| Rinses | Flow, conductivity, contamination, agitation, dwell | Controls carryover, staining, corrosion and bath contamination | Conductivity log, flow indicator, scheduled change |
| Deposit | Thickness, adhesion, composition, porosity, hardness, stress, appearance | Confirms functional output and process capability | XRF, coulometry, microscopy, bend/thermal tests, composition analysis |
| Post-treatment | Passivate concentration, pH, temperature, time, bake delay, seal | Controls corrosion performance and embrittlement relief | Batch record, oven chart, chemistry analysis, corrosion tests |
Hull Cell
A small test cell exposes a panel to a range of current densities. It helps assess brightness range, burning, low-CD coverage, contamination and additive condition. It is diagnostic—not a substitute for quantitative bath analysis.
Ampere-Hour Additions
Organic additive consumption may correlate with charge passed, but drag-out, carbon treatment, oxidation and load mix also matter. Ampere-hour dosing should be verified by performance tests and analysis.
Statistical Control
Trend chemistry, thickness, alloy content, CCE, defects, rectifier output and additions. Use control limits based on process behaviour and specification limits based on product requirements.
Anode-to-Cathode Surface Area
Cathode area drives the required current. Anode area and position influence current distribution, anode CD, dissolution, polarisation and metal-ion supply. There is no universal ratio: it depends on chemistry, soluble/inert anode design, loading and specification.
Control Plan Example
| Operation | Characteristic | Method | Frequency | Reaction |
|---|---|---|---|---|
| Alkaline clean | Concentration / temperature / water-break | Titration, calibrated sensor, visual test | Start/shift and defined interval | Hold load; correct bath; reclean; assess contamination |
| Activation | Acid strength / time / transfer | Titration and controlled timer | Start/shift and every load for time | Stop; correct; reactivate if permitted |
| Electroplate | CD, time, temperature, chemistry | Rectifier log, timer, sensor, analysis | Every load / scheduled analysis | Quarantine load; restore limits; evaluate strip/replate |
| Thickness | Local coating thickness | XRF/coulometry/microscopy as applicable | Defined sample per lot/load | Contain lot; review area/current/time and distribution |
| Post-treatment | Passivate/seal/bake parameters | Bath analysis, timer, oven recorder | Every load plus scheduled analysis | Hold product; assess reprocess and performance test |
Electrodeposited Metals and Alloy Systems
Search by purpose or metalComparison Table
| Deposit | Primary functions | Typical strengths | Key limitations / controls | Typical valency for Faraday calculation | Density g/cm³ |
|---|
Faraday’s Laws of Electrolysis
Charge → mass → volume → thicknessQ = I × t m = (I × t × M × η) / (n × F) thickness = m / (ρ × area)
Where Q is charge in coulombs, I is current in amperes, t is time in seconds, M is molar mass in g/mol, η is cathode current efficiency as a fraction, n is electron valency, F is the Faraday constant (approximately 96,485 C/mol), ρ is density and area is plated area.
The result is an average theoretical thickness. Real parts have local thickness variation from geometry, current distribution, anode placement, rack contact, shielding, agitation and chemistry.
Deposit Mass and Thickness Calculator
Required Time Calculator
Worked Example
A zinc load has 50 dm² plated area and is run at 2.5 A/dm² for 40 minutes. Total current is 125 A. Using Zn molar mass 65.38 g/mol, n = 2, density 7.14 g/cm³ and assumed CCE 95%:
- Charge Q = 125 × 2,400 = 300,000 C.
- Mass = Q × 65.38 × 0.95 / (2 × 96,485) ≈ 96.6 g.
- Area = 50 dm² = 5,000 cm².
- Volume = 96.6 / 7.14 ≈ 13.5 cm³.
- Average thickness = 13.5 / 5,000 cm = 0.00270 cm = about 27 µm.
This is illustrative. Actual efficiency and local distribution must be validated for the specific bath, load and operating conditions.
Interactive Defect and Cause Explorer
Use evidence, not guessworkStructured Troubleshooting Method
Contain and define
Identify affected lots, racks, positions, bath, time window, substrate, geometry and defect distribution.
Map the pattern
High-CD only, low-CD only, one rack side, one depth, one operator, one pretreatment line or one material batch?
Verify measurement
Confirm thickness, composition, pH, chemistry and inspection systems before changing the process.
Check recent changes
Additions, maintenance, new anodes, filters, water source, raw chemicals, rectifier, rack repair, supplier or load mix.
Separate preparation, bath and distribution
Use witness panels, Hull cell, coupons, contact checks and location mapping.
Correct, verify and prevent recurrence
Restore validated conditions, confirm on representative product and update controls, limits, maintenance or training.
Post-Treatments: The Deposit Is Often Only One Layer of the System
| Post-treatment | Science / function | Typical applications | Critical controls |
|---|---|---|---|
| Conversion passivation | Forms a thin reaction film on zinc, zinc alloy, cadmium or other deposits; modifies corrosion kinetics and provides barrier/self-healing behaviour depending on chemistry | Zinc, zinc-nickel, cadmium | Bath composition, pH, immersion time, temperature, rinse, drying, ageing and handling |
| Sealer / topcoat | Organic/inorganic layer reduces porosity, friction variation or electrolyte access | Fasteners, automotive zinc systems, decorative finishes | Film mass/thickness, cure, torque-tension effect, compatibility and repair |
| Hydrogen relief baking | Promotes diffusion of mobile hydrogen from susceptible steel before it concentrates at high-stress sites | High-strength steel after acid cleaning and electroplating | Delay to bake, temperature, duration, furnace uniformity, load arrangement and specification |
| De-embrittlement verification | Mechanical test demonstrates process control for susceptible product | Fasteners, springs, aerospace components | Specimen type, sustained load, test duration, lot correlation and failure criteria |
| Chromate-free/passivation alternatives | Uses trivalent chromium or non-chromium chemistry to provide corrosion resistance | Zinc and zinc alloys | Compatibility with alloy %, sealers, ageing and corrosion test performance |
| Anti-tarnish | Reduces surface reaction with sulphur/oxygen species | Silver, copper and decorative deposits | Electrical/contact resistance, solderability, film uniformity and shelf life |
| Reflow / fusing | Melts or restructures deposit to reduce porosity and improve solderability/appearance | Tin and tin-lead applications | Temperature profile, intermetallic growth, substrate heat effect and oxidation |
| Lubricant | Controls friction and installation behaviour | Threaded fasteners | Coefficient of friction, application uniformity, cure and compatibility with corrosion system |
Passivation Science
A conversion treatment partially reacts with the metallic coating and solution species to create an adherent inorganic film. It can reduce the rate of anodic metal dissolution, impede cathodic reactions and act as a barrier. Performance depends on film chemistry, thickness, defects, hydration, ageing and any sealer/topcoat.
Fresh passivates can be vulnerable. Excessive handling, hot rinsing, premature testing, abrasion or incorrect drying can damage the film before it matures.
Hydrogen Embrittlement
Hydrogen can be generated during pickling, electrocleaning and plating. In susceptible high-strength steels it can diffuse to stressed regions and reduce ductility, causing delayed fracture. Risk depends on strength/hardness, stress, microstructure, hydrogen input, traps and time.
- Minimise acid exposure and cathodic overcleaning.
- Use controlled plating CD and efficient baths where possible.
- Start relief baking within the specified delay.
- Do not assume baking repairs all damage or removes all hydrogen.
- Use approved alternative coatings/processes where risk is unacceptable.
Electroplating Science Learning Test
Question 1Standards and Technical Frameworks
- ISO 2080: vocabulary and conventions for metallic and inorganic coatings and surface treatment.
- ISO/TC 107: international standards work for metallic and other inorganic coatings and related testing.
- ISO 2081: electrodeposited zinc coatings with supplementary treatments on iron or steel.
- ISO 2082: electrodeposited cadmium coatings with supplementary treatments on iron or steel.
- ISO 1456: nickel, nickel/chromium and copper/nickel/chromium coating systems.
- ASTM B117 / ISO 9227: salt spray testing when invoked; these are comparative accelerated tests, not direct service-life predictors.
- ASTM B571: qualitative adhesion testing practices for metallic coatings.
- ASTM B487 / ISO 1463: microscopical cross-section thickness measurement.
- ASTM B568 / ISO 3497: X-ray spectrometric coating-thickness measurement.
- ASTM B504: coulometric thickness measurement.
Aerospace, Defence and Industry References
- AMS 2400-series and customer specifications: aerospace electroplating requirements for specific deposits.
- NAS, SAE, ASTM F-series and ISO fastener standards: hydrogen-embrittlement prevention, process control and testing where applicable.
- AIAG CQI-11: plating system assessment used in automotive supply chains.
- Nadcap Chemical Processing: accreditation and audit criteria for aerospace chemical processing where contractually required.
- AS9100 / ISO 9001: process validation, production control, monitoring, external-provider and nonconformity requirements.
- Environmental and safety law: metal finishing chemicals, air emissions, wastewater, worker exposure and hazardous substances require jurisdiction-specific compliance.
Reference Data Used by the Calculators
The Faraday constant is taken as approximately 96,485 C/mol. Atomic masses and densities are engineering reference values rounded for educational calculations. Actual deposited alloy density, valency, composition and cathode efficiency may differ and must be established for the controlled process.
Controlled-document warning: This application is educational. It does not reproduce standards or proprietary chemistry instructions. The contract, drawing, purchase order, current process specification, chemical supplier technical data and approved control plan remain authoritative.