High Velocity Aluminum Coatings
Numerous publications devoted to spraying aluminum by HVOF and cold spray processes display an industry need for a method to form a dense non-oxidized aluminum coating.
Spray clad aluminum coatings with such properties are used to repair/rebuild worn light-weight parts, to form a corrosion resistant layer with high electrical conductivity, to protect magnesium substrates and in additive manufacturing.
We are not aware of any research devoted to the HVAF deposition of Al coatings, so we just spray it in-house and produce specialized HVAF equipment for low-melting point materials spray cladding.
The Properties of HVAF Al Coatings
Kermetico HVAF Al coatings demonstrate a bulk-like structure, high bond strength and low level of coating oxidation.
Al powder nominal composition (wt.%):
- Aluminum 99.5%
Aluminum Coating Properties
| Apparent metallographic porosity | <1.0% |
| Hardness, HV | 105 |
| Maximum operating temperature, oC (oF) | 500(932) |
| Maximum coating thickness (as-sprayed), mm (inch) | 12 (0.500) and more |
Typical Cross- Sectional Micrographs of HVAF Aluminum Coatings
A Microstructure of a Kermetico HVAF Aluminum Coating, x100
A Micrograph of a Kermetico HVAF Clad Aluminum Layer, x500
A Comparison of HVOF, HVAF and Cold Spray Methods to Spray Pure Al coatings
The melting point of Al is 660°C (1,220°F), while the boiling point is 2,470°C (4,478°F)
Commercially available HVOF systems are not designed to handle low melting point metals. he typical combustion temperature varies from 3,100°C | 5,612°F for oxy-kerosene to 3,200°C | 5,792°F for oxy-hydrogen. Both are substantially higher than the boiling point of aluminum. This creates a risk of complete vaporization of the Al within the combustion chamber or nozzle, Al condensate build-up on the nozzle leads to clogging and the excess oxidation of the Al coating. Those risks make HVOF aluminum spraying an unfavorable candidate. This creates a risk of complete vaporization of the Al within the combustion chamber or nozzle, Al condensate build-up on the nozzle leads to clogging and the excess oxidation of the Al coating. Those risks make HVOF aluminum spraying an unsuitable candidate.
The cold spray deposition of Al is harder than other soft materials such as Zn and Cu. This is attributed to its high heat capacity which makes it harder to achieve shear instability conditions during impact, regardless of its low melting point and low yield strength. While some good samples of deposited Al were produced by different researchers, the overall cost of the cold spray process makes this application too expensive for industrial usage.
The Kermetico HVAF SL gun is designed specifically to spray low melting point materials.
It has:
- lower combustion temperatures (1,960-2,100°C | 3,560-3,812°F) than the boiling point of Al preventing material evaporation
- inert gas shroud minimizing oxidation
- wide nozzle preventing nozzle clogging
- higher particle velocity than HVOF and higher particle energy than Cold spray
- lower investment costs and much lower operating costs than HVOF or Cold Spray
All of this result in affordable Al coatings with close to zero porosity, zero gas permeability and high bond.
The Typical Applications for Kermetico HVAF Aluminum Coatings
- Repair of worn light-weight parts made of aluminum, magnesium or its alloys
- Corrosion protection of magnesium parts
- Functional coatings
- Additive manufacturing
HVAF Equipment to Spray Aluminum Coatings
Kermetico has developed a specialized gun to spray Al and Al alloy powders: Kermetico SL.
You may also be interested in the rest of our HVAF equipment to spray different materials:
- Convertible HVOF and HVAF equipment:
- Multi-purpose HVAF AK systems, with a variety of spray guns:
- Specialized HVAF S equipment family:
- Additional equipment:
- An HVAF grit feeder for the grit blast preparation of parts to reduce coating costs
- A Gas Permeability Tester for an instant check of a coating’s through porosity
Kermetico, Inc. –Material Science Excellence, HVAF and HVOF Equipment Manufacturing and Thermal Spray Coating Services Since 2006
We create equipment that helps material scientists, engineers and business managers achieve their goals.
We have installed more than 60 Kermetico HVAF systems in the USA, Europe, Japan and China.
Some of the systems are at work in Universities and National Labs, but most of them are used in production thermal spray shops.
We proudly design and produce our HVAF thermal spray equipment in California and install it all over the world.
You can visit our R&D center in Benicia to meet our designers and see our HVAF and HVOF equipment in action.
We also deposit HVAF and HVOF thermal spray coatings for customers in North America – ourselves and through our network of partners.
