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What coating is on my Aluminum Nickel Bronze parts?

I am trying to figure out what type of finish is on an existing part that I am redesigning. The geometry will change slightly but the base material (Aluminum Nickel Bronze) will stay the same & the finish will be the same. I have never had to "spec-out" a finish for this type of material. Since I am color blind I will try to describe the color & texture of the existing finish. It is a gold(ish) green color that you can see machining marks through & is "streaky" in consistency. I know it is for corrosion protection & hydraulic fluid protection. If I could get the SAE or MIL or ... specification for this finish it would help me decide what to place on my drawing. Oh, the material has very, very weak magnetic capabilities. Thank you very much!

Denny Falls
Engineer - Woodland Park, Colorado, USA
2007

Hi Denny!

My guess is that the aluminum nickel bronze was chromate conversion coated: or, maybe not coated and just left to develop a patina. It's not common in aerospace practice to insist that Al Ni Bronze parts be protected- at least, my company doesn't have corrosion resistant coatings on the parts we make from the stuff.

And it's the roughly 5% iron that gives it the magnetic characteristics. That makes it a nice show and tell piece I often use when I give talks to elementary and middle school kids on elements.

Lee Gearhart
metallurgist - E. Aurora, New York
2007

2007

Lacquers may be used on these alloys, but perhaps there isn't any applied coating. Aluminum bronzes are naturally gold color, and greenishness may be natural patination. Streakiness may indicate cast material or staining from fluids. Some common aluminum nickel bronzes having magnetic properties are given below, along with some common AMS, ASTM & SAE standards. Many MIL & QQ standards also exist (mostly canceled).

Casting alloy standards -- ASTM B148 Sand castings, ASTM B271 Centrifugal castings, SAE J462 Cast copper alloys:
UNS C95500: 81Cu-11Al-4Fe-4Ni, magnetic permeability 1.2-1.3.
UNS C95800: 81Cu-9Al-4Fe-4.5Ni-1.5Mn, magnetic permeability 1.05.

Wrought alloy standards -- ASTM B150 Rods, bars & shapes, ASTM B283 Die forgings, SAE J463 Wrought copper & alloys:
UNS C63000: 82Cu-10Al-3Fe-5Ni, magnetic permeability 1.05. AMS 4640 Rods, bar & forgings.
UNS C63200: 82Cu-9Al-4Fe-5Ni, magnetic permeability 1.04.

SAE J461 Wrought and Cast Copper Alloys describes the various alloys and their properties; useful when selecting alloys for various purposes. SAE J462 & J463 are mostly specification tables.

For more info: www.MatWeb.com, www.ampcometal.com or http://nbm-houston.com/products.html

Ken Vlach [deceased]
- Goleta, California

Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

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