Aluminum Coating Properties

Physical and Mechanical Properties of High Purity Electroplated Aluminum

Electroplated aluminum has been fully characterized through in-depth investigations of its physical and mechanical properties.

AlumiPlate® aluminum is a high purity coating 99.99% pure. Multiple characterization efforts have documented the most important metallurgical properties of this plated deposit.

The collected data are presented below in tabular form:

Table 1 – Physical and Mechanical Electroplated Aluminum Properties

CharacteristicElectroplated Aluminum
Purity>99.99%
Density2.67 g/cm3
Electrical Resistivity2.95 μW·cm
Thermal Conductivity218 J/smK
Melting Point660 °C
Elongation of Fracture>50%
Microhardness22-25 HV 0.015
Taber Abrasion (Plated Surface)28 mg/1000 cycles
Internal Stress15 N/mm2
Ring Shear Test70-90 N/mm2
Recommended Pore Free Thickness> 8 μm (0.0003")
Coefficient of Frictionμ ca. 0.16

A more detailed list of reference properties of pure aluminum is available as well.

Purity – electroplated aluminum is 99.99% pure. The coating is free of alloying elements, with extremely low levels of contaminants and impurities. Purity is monitored on a regular basis using high resolution Glow Mass Discharge Spectrometry (GDMS). For representative purity data, see our semiconductor applications page.

Thickness – The AlumiPlate® Al plating process can uniformly deposit thin or thick layers. Applications requiring thick layers for subsequent machining or material build-up for parts salvage can benefit from the process. Engineered components are routinely plated with thicknesses of 0.0001″ – 0.015″ (2 – 400 µm), or more.

Coefficient of Thermal Expansion (CTE) & Cryogenic Use – Electroplated aluminum performs well at cryogenic temperatures. Materials and substrates that have significantly different CTE to electroplated Al benefit from the plating’s low internal stress, high ductility and excellent adhesion. Electroplated aluminum has been used in commercial and scientific devices operating at cryogenic temperatures, here on Earth and out in space.

Torque & Tension – With a surface friction modifier, aluminum electroplated fasteners have consistent, low dispersion and predictable torque/tension properties. Testing for fasteners in military applications shows electroplated Al fasteners match the surface properties of cadmium plated fasteners, while providing improved corrosion protection and minimizing embrittlement concerns. The surface modifier and resultant tightening torque factor can be engineered to offer a “drop-in” solution for your fastener application. Pure aluminum plating complies with NAS 4006 fastener coating requirements.

Internal Stresses – Unlike other plating processes, electroplated aluminum has very low internal stresses. It is an excellent choice for very thin parts that require corrosion protection but are susceptible to warping from highly-stressed coatings, temperature gradients and differences in CTE. Electroplated aluminum can be used to electroform high purity aluminum foils.

High Temperature Resistance – The melting point of aluminum is 1,220 °F (660 °C). AlumiPlate aluminum will protect surfaces from corrosion at significantly higher temperatures than virtually any other conventional plated metal.

· Significant testing by the aerospace industry has shown that AlumiPlate aluminum plating is able to withstand and protect high strength steel up to 350° C.
· Semiconductor industry extensive testing for short duration high temperature applications have verified excellent AlumiPlate aluminum performance up to 450 °C.

Unlike many conventional plating systems, which are destroyed or lost at higher temperatures, AlumiPlate aluminum offers excellent protection for base metals in high temperature applications.

Electrical Conductivity – The electrical conductivity of 99.99% (4-nines-pure or Al4N) aluminum is approximately 62% that of copper. Pure aluminum is one of the best conductors amongst the non-precious metals. The coating offers better material compatibility at a lower cost than expensive gold and silver coatings for many applications. Pure aluminum plating excels as a protective coating for electrical connectors in severe environments, such as the hermetic connector for the Auxiliary Power Unit of the Lockheed Martin F-35 Lightning II (carrier variant of the Joint Strike Fighter).

Thermal Conductivity – AlumiPlate aluminum has three times the thermal conductivity of steel and can be used as a thermally conductive, corrosion resistant coating which can offer excellent matching of thermal expansion coefficients and materials compatibility. High purity aluminum exhibits superconductivity at temperatures near absolute zero (Tc 1.2 K).

Ductility / Formability – Aluminum is a soft and ductile metal. Elongation of 50 to 65% without fracture has been measured. Over a ductile substrate, the pure plated layer can be bent, flexed, stretched, rolled, drawn, swaged or machined without cracking or peeling. The outstanding malleability makes AlumiPlate aluminum the perfect choice for corrosion protection applications requiring forming and crimping after plating.

Density – The dense non-porous nature of AlumiPlate Al is a unique property of the amorphous, pore-free coating structure. A thin 0.0003″ (8 µm) layer ensures a pore-free aluminum coating and physically protects the underlying material, contributing to the plating’s outstanding corrosion resistance. A thick dense layer of pure aluminum acts as a barrier to migration and diffusion of substrate impurities into vacuum or controlled environments, sensitive to minute levels of contaminants.

Uniformity – As an electrolytic plating process, aluminum plating follows the same physical rules governing other electroplating processes such as Cd or Zn. In other words, if a component is currently Cd plated, electroplated aluminum offers an immediate “drop-in” replacement with similar uniformity and control. Unlike other “line-of-sight” processes, aluminum electroplating can be used for complex geometries, inside diameters and interior surfaces (see Throwing Power for more information). Critical semiconductor and aerospace parts that require tight plating control are excellent candidates for the process.

Throwing Power – The aluminum electroplating process is a true electrodeposition process using non-aqueous, liquid baths. Parts with complex geometries and small inside diameters can be plated with an even layer of aluminum. Supplementary anodes, current thieves and robbers, and plating parameters can be optimized based on the individual component geometry. AlumiPlate Inc. has developed special techniques, waveforms and tooling to plate into small through-holes and interior surfaces of semiconductor equipment components.

Adhesion – Aluminum plated parts have excellent adhesion and can be expected to pass all destructive and non-destructive adhesion tests per ASTM B-571 (Standard Practice for Qualitative Adhesion Testing of Metallic Coatings). For quantitative determination of adhesion, an internally developed test using a Pull-Off Adhesion Tester has shown adhesion strength in excess of 60 MPa (8.6 ksi).

Anodizability – The pore-free coating allows aluminum electroplated plated parts to be clear or hard-coat anodized. AlumiPlate aluminum can be plated onto and anodized on nearly any conductive substrate including but not limited to steels, copper, aluminum alloys, stainless alloys, beryllium and metal matrix composite materials and other various alloys.

The aluminum oxide (alumina) layer formed by anodizing is non-conductive and can be a good electrical insulator, especially in high temperature applications. Furthermore, the Al2O3 alumina coating obtained from anodized Al electroplating is purer and more consistent than that of anodized Al alloys. Anodized electroplated aluminum has shown increased corrosion protection (HCl bubble testing), higher breakdown voltage and significantly lower levels of contaminants, for semiconductor use.

Cosmetic Applications – Due to its high purity, density and thickness capability, electroplated aluminum can be finished with techniques developed for aluminum alloys. Cosmetic and color anodizing, electropolishing, bright-dips, chemical and electrocleaning, texturing, and many more, are now available on any material, not just aluminum! Furthermore, these techniques are typically improved when performed on the pure electroplated aluminum coating.

The capability to permanently color the surface of anodized aluminum makes the AlumiPlate layer an attractive choice for a wide variety of appearance or performance reasons. The coloring could be used to color-code different types of components. Applications abound where aesthetics play an important role such as in the Medical, Marine, Recreation, Automotive, Decorative, Sporting Goods, Die Casting, Jewelry and many other industries.

Ceramic and Diffusion Processes – Recent developments in the aluminum industry have resulted in electrochemical processes to convert the surface of aluminum alloys into high temperature ceramics and intermetallics. These coatings have very high hardness, high temperature capability and the potential for very high dielectric strength (oxides only). Stainless steels and high temperature Fe, Ni, Cr & Co alloys can now benefit from oxide and aluminide coatings previously only available on aluminum alloys. High voltage potential processes like plasma electrolytic oxidation (PEO), electrolytic plasma oxidation (EPO) or microarc oxidation (MAO) can transform electroplated aluminum into an electro-ceramic oxide coating. Heat treatments can be used to create high temperature surface aluminides as the pure aluminum coating diffuses into the substrate.

Fatigue – The ductile aluminum coating typically has low internal stresses and a very low notch sensitivity factor resulting in no significant fatigue debit. The fatigue performance of aluminum plated components has been well tested by aerospace OEM’s for critical load parts such as flight-safety-critical landing gear components.

Contact us for more information or to learn about our electroplated aluminum coating properties in more detail.