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A survey of more than two hundred aerospace manufacturing professionals demonstrated a lack of understanding about cadmium, a highly toxic metal that is still being used frequently in the U.S. aerospace industry.

The poll, conducted by the selective plating company SIFCO ASC, suggests that more clarity on cadmium is needed before respondents can make informed decisions about the chemical coating element and possible alternatives.

What is Cadmium?

Cadmium, a heavy metal found in zinc ores, is often used in the aerospace industry to provide corrosion protection on landing gear, airframe structures, flap tracks, and any components where bare steel is present. The element features consistent torque-tension and electrical conductivity characteristics.

The metal, however, is being phased out in the U.S. aerospace sector, due to its critical health effects. Since a Restriction of Hazardous Substances (RoHS) directive in 1993, cadmium has been one of six highly toxic substances banned from use in Europe in electrical and electronic equipment.

A highly toxic cyanide bath is commonly used to produce cadmium deposits, and cadmium itself damages the kidney’s blood filtration system. The metal has also been linked to skeletal damage and lung cancer.

SIFCO ASC, a supplier of contract selective electroplating and anodizing services, provides both cadmium and zinc-nickel touch-up kits to OEMs and “Maintenance, Repair, and Overhaul” (MRO) companies. The Independence, OH-based company believes that zinc nickel is the closest alternative to cadmium, and is in some cases superior.

When used with a passivation process known as trivalent chromium conversion, the zinc-nickel provides a more environmentally friendly way of protecting against salt spray, according to SIFCO. Other alternatives to cadmium include zinc-iron/zinc-cobalt and tin-zinc.

The Survey Says

The cadmium-focused survey featured responses from 201 engineers and engineering managers in manufacturing & production; testing & quality control; and research & development environments. Two thirds of the respondents — some who plate cadmium — cited aerospace specifications and requirements as their biggest barriers to phasing the element out of manufacturing processes.

Aerospace specifications are unlikely to mandate a cadmium alternative, according to the Ohio plating provider, because of the financial impact of changing an established process; the lack of sources that can provide a zinc-nickel or cadmium alternative; and the absence of a government order requiring new specifications to be written.

“The specifications themselves don't act as barriers to the phase-out, but [there is] reluctance to change the specification to a cadmium alternative,” said Scott Peterson, Training Manager at SIFCO ASC.

More than 50% of poll respondents believed they have no other option for corrosion protection.

“We are dependent upon what the [original equipment] manufacturer specifies when it comes to corrosion resistant plating,” said one aerospace engineer surveyed. “Until the manufacturer allows alternatives, our hands are tied.”

According to SIFCO’s Peterson, the shift away from cadmium must be driven by the OEM market, not by military aircraft manufacturers.

“Boeing has been pushing for a change from cadmium for the last 20 years, but there is still no real drive from governments, OEMs, or any other bodies forcing this change through,” Peterson said.

To provide clarity on the heavy metal, SIFCO ASC has created an online Cadmium Knowledge Hub where its technical experts will regularly share a variety of content on the topic, such as manufacturer testing reports and academic research papers. The site also encourages other professionals in the industry to submit their own findings.

The primary reason why no real alternative has been mass-adopted in the U.S. aerospace sector to date, said Peterson, is the perceived risk of switching from a deposit that OEMs are confident can deliver the right sacrificial corrosion protection to one which has yet to be proven when used in high volume.

“What this survey really shows is that there is much hesitation across the industry on this topic,” said the SIFCO manager. “We believe that this highlights a need for more knowledge sharing and collaboration to provide the level of confidence needed to make the change.”

What do you think? Will the aerospace industry successfully phase out cadmium? Send us your comments below.

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