The World of Pure Aluminum
Aluminum is an important engineering material due to its low density and high corrosion resistance. Unlike other light metals, including magnesium and beryllium, it passivates in oxygen environments and is not toxic, making it an ideal structural metal when weight savings is a concern. Pure aluminum is highly abundant, making up 8% of the Earth’s crust, and can be found in over 270 naturally occurring minerals.
Pure aluminum is of special interest for its improved corrosion resistance, high ductility, high electronegativity and low atomic weight for surface finishing solutions. Dense, thick and very pure aluminum (typically more than 99.99% pure) can be deposited as a protective coating via the AlumiPlate® Aluminum Electroplating process. This electrodeposition process has attractive characteristics such as tight control capability, ability to throw into holes and it can be used to build pure aluminum layers hundreds of micrometers thick.
Aluminum platings used as a surface finishing solution can enhance and protect the surface of other structural metals and composites to improve the material’s performance in the end-use environment. The pure aluminum coating can be heat treated to form intermetallics with high wear, abrasion and a working temperature envelope of up to 900 °C.
Common Questions About High Purity Aluminum
What is Pure Aluminum?
Pure aluminum is a soft, silvery-white, ductile and non-magnetic metal that belongs to the boron group and identified by the atomic number 13, because its atoms contain 13 electrons and 13 protons. To be considered pure aluminum, the metal needs to consist of 99% aluminum. Pure aluminum properties include an electrical conductivity that is twice as high when compared to copper, with a thermal conductivity that is about three times greater than steel, making it an ideal material for heating and cooling applications. It is also characterized by its high reflectivity and resistance to oxidation.
All of the attractive characteristics of pure aluminum are now available as a pure aluminum coating. AlumiPlate Inc. offers the process of electroplating components with high purity aluminum.
Is Aluminum Found as a Pure Metal?
Due to its high affinity for oxygen, aluminum is typically found in oxides or silicates and not in its elemental form. Pure aluminum has limited use as the base substrate for engineered components due to its lower mechanical properties relative to aluminum alloys. Pure aluminum is available as a substrate from industrial suppliers.
More importantly, pure aluminum as a coating is available through vacuum and wet metalizing processes. AlumiPlate Inc. can electroplate your component with a high purity coating of typically greater than 99.99% Al using a wet, non-aqueous electroplating process.
Where is Pure Aluminum Found in Daily Life?
Pure aluminum can be found in powerlines, beer kegs, window frames, vehicles and kitchen utensils. When you fly for travel, you are most likely to have benefited from pure aluminum. Most commercial aircraft bodies are fabricated from clad aluminum. Clad aluminum is made by roll forming a high purity aluminum alloy onto higher strength structural aluminum. In fact, one Boeing-747 consists of 147,000 pounds of aluminum.
Why is Pure Aluminum Becoming More Common in Product Design?
In the past, metals like lead and copper were used for piping, plating and building structures. As time went on, it became evident that lead is poisonous to humans and is now banned from use in many products. Although copper is a better conductor of heat than high purity aluminum, it is more costly to manufacture and therefore is not often used in modern day construction.
Engineered components must increasingly survive harsher environments or simply last longer in normal use by today’s standards, while complying with environmental regulations. Pure aluminum offers a 100% recyclable and non-toxic protective option for steel, copper, magnesium, aluminum alloys and composites while being a productive heat conductor.
Electroplated aluminum outlasts other metal, organic and inorganic coatings in severe environments (sodium chloride or sulfur dioxide) and can easily withstand temperatures of up to 400 °C. Aluminum platings are non-toxic, recyclable and compliant with newer environmental standards (such RoHS). Electroplated aluminum can be used as drop-in replacement to toxic cadmium and provides better protection than nickel platings.
Harnessing High Purity Aluminum Properties
High purity aluminum has unique attributes which make it attractive for a variety of uses across many industries. Its practicality, cheap manufacturing and abundance, are just a few examples of why it is so commonly used.
Aluminum electroplating shares all of the beneficial properties of pure aluminum, including:
Corrosion Protection
Pure aluminum passivates in oxygen, shielding itself from its outside environment. A protective aluminum oxide immediately forms upon contact with oxygen and it reforms (“self-heals”) when scratched.
Pure aluminum is anodic to steel, copper and even other aluminum alloys. As a sacrificial coating, 99% aluminum dissolves before the substrate, galvanically protecting and extending the life of the base material. Electroplated aluminum aids in corrosion prevention of other metals by acting as both a barrier coating and a sacrificial coating.
Lightweight
Pure Al is about three times lighter than steel, with a weight of 2.7 g/cm3. Aluminum is used extensively in the aerospace and semiconductor fabrication industries.
Aluminum coatings are lighter than other metal coatings, nickel or zinc-nickel alloys for example.
Due to its corrosion prevention, electroplated aluminum is ideal for applications where lightweight materials require corrosion resistance or electrical conductivity. Aluminum alloys, beryllium, magnesium, titanium and metal matrix composites can benefit from typically higher than 99% pure aluminum coatings.
Electrical and Thermal Conductivity
High purity aluminum is an excellent electrical and thermal conductor (about 3/5’s as much as copper), an ideal material for major power transmission lines.
As a coating, it improves the performance and life of electrical and thermal components. Aluminum plated electrical connectors and heat sinks are protected from corrosive environments and fluids, while maintaining high electrical and thermal conductivity.
Malleability and Ductility
Electroplated aluminum is highly ductile and maintains a low density and melting point. Plated components can be formed, swaged or crimped allowing for more flexible fabrication cycles and easy malleability.
Heat Resistance
Pure aluminum has a much larger temperature envelope than other metal coatings. Unlike tin (Sn), silver (Ag), cadmium (Cd), and zinc (Zn), pure Al melts at 660 °C, with an effective temperature range of up to 400 °C. Alloyed coatings of zinc, cadmium, and zinc-nickel may degrade or change in composition at elevated temperatures upon thermal cycling, a phenomenon that does not affect electrodeposited aluminum.
Additionally, the aluminum plating can be diffused into high temperature alloys (stainless steels and superalloys) to form a surface aluminide. Aluminides have high wear, corrosion resistance and have been used in temperatures ranging 900-1100 °C.
Low Hydrogen Embrittlement Risk
High purity aluminum electroplating uses a non-aqueous and aprotic (H+ free) chemistry. There is no source of free hydrogen that could be absorbed by high strength steels (4140, 4340, M30, 300M, Aermert 100, springs steels) and other hydrogen-embrittlement sensitive materials.
Pure aluminum is an ideal coating for high strength components in corrosive environments, such as landing gears, pins, actuators and critical service fasteners.
Anodization
Chromic, sulfuric (hardcoat), oxalic and mixed acid anodization are possible on pure electroplated aluminum enabling anodization of steel, copper and alloyed aluminum. Because of its high purity, alumina is derived from pure aluminum and has lower contaminants, voids and shows improved corrosion resistance (via “HCl bubble test”) and higher breakdown voltage for an anodic oxide finish.
Superconductivity
Aluminum in elemental form can exhibit superconductivity at 1.2 K, offering no resistance to electrical current. Applications for superconductors include magnetic levitation (maglev trains), medical biomagnetic devices (magnetic resonance imaging MRI), high energy physics research (Fermilab and CERN LHC equipment) and quantum computing.
Reflectivity and Emissivity
Pure aluminum properties make it a productive reflector of heat as well as visible light. Pure aluminum is often used as a material for reflectors and other applications where lightweight materials are used. In fact, aluminum-coated roofs keep homes cool by reducing internal solar heat and reflecting up to 95% of sunlight.
Pure aluminum allows for the capture of light in a broad spectrum, with the highest reflectance of any metal in the ultraviolet and infrared spectral range and behind silver in the visible light and near-infrared.
The Mauna Kea Observatory utilizes cryogenically-cooled aluminized metal mirrors for its astronomical equipment. Electroplated aluminum is diamond machined to a low surface finish with high conformance to the mirror surface figure and finish requirements.
The high ductility and low internal stresses of pure plated aluminum reduce distortion errors related to the different expansion rates of the various materials, even at cryogenic temperatures.
Thermal Conductivity
The thermal conductivity of high purity aluminum is known to be much higher than other common metals, like copper and steel. It has three times the amount of thermal conductivity of steel and two times that of copper. It is often used for heat sinks for circumstances that require heat to be drained away quickly, such as in LED lights and computer motherboards.
Thermal components can be aluminum plated to reduce corrosion with cooling fluids or the end-use environment. Thermal components requiring a di-electric, non-conducting surface can be anodized after aluminum plating.
Pure Aluminum — A Formula for Countless Applications
Because aluminum properties are so versatile, high purity aluminum has a wide range of possible applications. Pure Al excels as a surface finishing solution due to its non-toxicity and ability to act as an anti-corrosion agent, allowing products to sustain higher temperatures and increasing their lifespan.
AlumiPlate’s research surrounding pure aluminum has opened up new application possibilities, and many of these are just beginning to make an impact across a wide range of industries. Leading aerospace, semiconductor, laser, transportation, and alternative energy OEM’s rely on AlumiPlate’s electroplating coatings to protect components in aggressive environments or exposed to high temperatures.
Aerospace
Pure aluminum has been used in aerospace technology since the 19th century, before the first airplane was invented. Its lightweight and corrosion prevention properties make it ideal for aerospace manufacturing.
Since WWII, cadmium has been used in aerospace as an anti-corrosive coating, but was soon found to be toxic due to its tendency to leach and cause environmental pollution. High purity aluminum is now the preferred cadmium replacement for high strength aerospace components, offering improved corrosion resistance and complying with environmental regulations and guidelines.
Due to aluminum’s high electrical conductivity, it is an ideal material for electrical connector shells used for all military systems.
Other aerospace applications include:
- Applications that require MIL-DTL-83488 coatings
- Bearings, fasteners and other hardware calling for NAS 4006 coatings
- High strength, flight safety, and critical components (landing gear, pistons, pins)
- Cadmium replacement
- Electrical connectors
- Rivets
- Drop-in replacement for IVD Al (ion vapor-deposited aluminum)
Construction
Because of its lightweight design and corrosion protection, pure aluminum is used widely throughout the construction and building industry. Commonly used in finishes, windows, domed roofs, panels and other building materials, high purity aluminum is durable, eco-friendly and does not require any kind of special maintenance, making it low-cost over time.
Pure aluminum also has reflective properties that reduce energy consumption, including the cost of lighting and heating. Because it does not burn, it is considered non-combustible, making it ideal for buildings and construction. In the construction industry, high purity aluminum is an excellent option for coastal and marine windows and hardware. Its high corrosion protection allows for the replacement of stainless steel with aluminum plated carbon steel. Additional color anodization is also available for high end commercial and residential use.
Heavy Equipment
When it comes to heavy equipment, pure aluminum is a budget-friendly option. For machinery that has weight restrictions, it is ideal because of its lightweight design. For heavier equipment, aluminum is used as a protective coating for high strength fasteners and hardware. Heavy equipment relies on high strength fasteners for critical joints in cranes, bulldozers, backhoes and excavators. Sensitivity to environmentally assisted corrosion is of special concern in heavy equipment, where high strength parts are exposed to corrosive environments while under high mechanical loads. Additionally, testing of electroplated aluminum components has shown no fatigue debit or degradation.
Semiconductor Production Equipment
99% Aluminum can be uniformly deposited into any type of thickness, making it ideal for semiconductor production equipment. For chemical vapor deposition chamber interiors, aluminum enables higher performance and a longer life for the critical semiconductor etching and deposition process components.
Electroplated aluminum protects semiconductor fasteners, straps, rings and flanges at temperatures up to 400 °C. The pure and dense aluminum coatings prevent the diffusion of substrate contaminants into the chamber environment.
For components that are directly exposed to plasma, the plating can be anodized to yield purer and void-free alumina than anodization of Al 6061 or Al 6063 alloys.
Superalloys and stainless steels can be protected with the aluminum coating. The plating can be diffused into stainless steels and superalloys (such as Hastelloy and Inconel) to form an intermetallic aluminide for additional protection and higher temperature capability.
Agricultural Equipment
In the agriculture industry, high purity aluminum is used as a coating for hydraulic hose hardware. Pure aluminum combats corrosion of hose shells and couplings used in fertilizer applications. Expensive stainless steel hose fittings can be replaced with aluminum plated carbon steel fittings for marine use.
Specialty Metal Optics
Because of its reflective properties, Pure Al is used as a reflective coating on mirror surfaces. In the visible light and near-infrared ranges, aluminum has the highest reflectability behind silver, making it ideal for specialty optics. Pure aluminum can be used to replace nickel coatings on metal mirrors and other specialty optics. Lightweight Al 6061, AlSiC, Al-Be mirrors are susceptible to surface figure distortions due to the CTE mismatch with heavy nickel coatings. Aluminum electroplated metal optics do not suffer from bimetallic issues, with almost zero distortion at cryogenic temperatures.
Marine and Offshore Applications
Aluminum is non-toxic, eco-friendly and recyclable, making it a natural choice for marine and offshore applications. It offers corrosion protection, high strength-to-weight ratio, formability and flexibility to both interior and exterior marine applications or parts exposed to seawater sprays.
In the marine industry, high purity aluminum is used to manufacture:
- Deck Hardware
- Lighting and cabin fixtures
- Hull fitting to aluminum structures
- Offshore rig decks
- Hydraulic fittings
- Hoses
- Replaces stainless steel with Al plated carbon steel
Academic Research
Pure aluminum has intrinsic properties extremely valuable to important areas of research due to its low atomic (Z) number, low neutron cross section, scattering characteristics and superconductive behavior at 1.75 K. High energy physics experiments, fission, nuclear physics, and quantum computing require tick, pure and dense aluminum for cutting edge applications and research.
Controlled deposits of extremely thick and pure aluminum are possible via aluminum electrodeposition. Pure Al coatings yield uniform plating of small or complex part geometries or with high aspect ratios.
Pure Al as a Cadmium Plating Alternative
Since research was conducted in 1995, the use of cadmium plating as an anti-corrosive material has been restricted because of its tendency to leach and contaminate surrounding environments. Since the late twentieth century, high purity aluminum has been used as a cadmium plating alternative. Electroplated aluminum is the preferred coating alternative for high-strength components in critical applications that cannot fail due to corrosion. Pure aluminum mitigates galvanic corrosion with more noble metals, similar to cadmium. The latest military and commercial aerospace programs use magnesium and conductive composites. These materials are corrosion-prone and can be protected without the environmental concerns and low temperature limits of cadmium.
Pure Al as a Zn Alloy Coatings Alternative
Zinc alloy coatings have a long history of use in automotive applications. More recently, zinc alloy coatings (zinc-nickel and tin-zinc) have been developed for use in the more demanding aerospace environment.
These alloy coatings are sensitive to compositional variation which affects their performance and temperature capability. As a heavy metal, nickel has been targeted for present and future reduction by environmental regulations. Aerospace OEM testing has shown that Zinc-nickel plated components can suffer from hydrogen embrittlement or field re-embrittlement.
Electroplated aluminum offers improved corrosion performance without the pitfalls of zinc alloy coatings.
| Specs | AlumiPlate® AL | LHE ZnNi |
|---|---|---|
| Nominal Recommended Thickness | 0.0003" | 0.0003" |
| SO2 (ASTM G-85) Performance | 668 hrs | 168 hrs |
| Salt Spray (B-117) Performance | 1000+ hrs | 1000+ hrs |
| RoHS and REACH Compliant | Yes | Yes (Now), Future(?) |
| Uniform Composition and Purity | Yes, 99.99% Al | No (5-10% Ni) |
| No HE, No Re-Embrittlement & No 24-Hr HE Bake | Yes | No |
| High Temperature Capability | Up to 1000 °F | Up to 1000 °F |
| Sacrificial Protection | Yes | Yes, but lower |
| No Galvanic Reaction with SST, Ti, BeCu, AlNiBr | Yes | No, in salt water |
| Process Not Susceptible to Organic Contamination | Yes | No |
| Bath Agitation Unrelated to Coating Embrittlement | Yes | No |
| No Anode Degradation Risk or Coating Impact | Yes | No |
| Ductile, Formable and Stampable | Yes | No |
| Anodizeable | Yes | No |
Table 1: Properties and benefits of electroplated aluminum versus ZnNi.
Environmentally Friendly Plating Solutions
To create long-lasting and reliable infrastructures in today’s society, as environmental concerns continue to rise, relying on an environmentally friendly coating is essential. High purity aluminum is the ideal environmentally friendly coating alternative. It outperforms toxic and heavy metal coatings, it is recyclable, it is abundant (not a scarce precious resource) and it complies with global regulations to help the environment.
ROHS & REACH Compliance
To ensure a high level of protection for humans and the environment from exposure to chemical substances, the EU put forth the ROHS and REACH Compliance regulation in 2007. This directive requires manufacturers to register their materials and prohibits the use of:
- Lead
- Mercury
- Cadmium
- Hexavalent chromium
- Flame Retardants PBB Type
- Flame Retardants PVDE Type
Aluminum alloys produced through recycling do not need to be registered because they are not harmful to the environment and do not leach heavy metals. High purity aluminum is a 100% recyclable and sustainable metal, creating competitive advantages for your business, and more importantly, helping to keep our environment clean and safe.
Eco-Conscious Enclosed and Automated Processing
To eliminate harmful coatings like cadmium from production, AlumiPlate uses eco-conscious plating equipment. State-of-the-art automation and software monitors and controls the plating in a fully enclosed and automated line.
In addition to the benefits of automation for repeatability, a fully enclosed line limits operator exposure and process wastes. The various plating line liquid and gas systems can be captured and recycled with the potential for zero process emissions.
By eliminating toxic coatings with safe pure aluminum and minimizing hazardous emissions of other plating techniques, high purity aluminum creates an affordable and sustainable process.
Do You Have a Challenge Whose Solution Involves Pure Aluminum?
Pure aluminum’s high corrosion resistance and high temperature performance make it an ideal and competitive, environmentally friendly coating for modern use. High purity aluminum’s applications throughout the aerospace, construction, heavy equipment, agricultural, semiconductor, marine and academic industries result in high-performing, innovative, sustainable and durable products.
AlumiPlate is committed to the development and improvement of its high purity aluminum plating process. To inquire into our novel products and services, Contact Us by phone call or email to customize a solution for your unique application and receive more information.