Perhaps you’ve seen it in an old movie, or heard about it in conversation: historically, people would bite gold coins to check their authenticity. This approach works for one simple reason – pure gold, along with other noble metals, is soft. Malleability is a remarkable and desired quality for precious metals, along with other desirable traits. However, characteristics such as conductivity or corrosion resistance, must be supplemented with strength and wear resistance.

Metal’s Natural Magic

What makes metal a preferred choice for so many components and applications is its inherent ability to deform. Metal can be bent, rolled, coined, and drawn. Its ability to deform is due to its crystal structure, which allows atoms to move and be rearranged under stress. This doesn’t happen with other materials, since their crystal structures are fixed.

But this flexibility also has major drawbacks, limiting its ability to be used in pure form. A sliding electrical contact made of pure palladium would quickly wear away. A dental crown made from pure gold will dent and lose its shape. Pure metals simply can’t hold up to the demands we put on them.

This is why we alloy them.

Balancing Desired Alloy Properties

Ultimately, alloying is more of an art form that seeks to find a precise balance between natural properties, such as conductivity and malleability, with strength and wear resistance. That’s it. We could stop there. But let’s look closer at the demands of electrical contacts and related components:

Strength / Hardness – enough is required to withstand mechanical stress, wear, and deformation. Requirements will vary depending on how the part is used or how often it will be cycled. Sliding contacts, as mentioned earlier, are more demanding since they are constantly moving and subject to ongoing mechanical damage. Many contacts also act as a spring element and require a high strength to maintain the contact pressure without deforming.  Separable or mating connectors, such as those found on PCB card edges, are not continuously exposed to friction and as a result don’t need to be as strong.

Corrosion Resistance – a clean, tarnish free surface is required for the proper functioning of electrical contacts, medical implants, and dental restorations. Corrosion resistance is a defining characteristic of noble metals like gold, platinum, and palladium, and a main reason for their widespread use.  Corrosion resistance tends to be decreased with the addition of semi-noble metals like silver or base metals like copper, however careful alloy design can maintain the needed corrosion resistance to preserve a clean metal surface while allowing the introduction of lower cost strengthening elements such as silver or copper. 

Conductivity – another key requirement for most applications is that alloys must efficiently allow electricity or data signals to pass through. Silver and copper lead on conductivity, with gold coming in third. Palladium-copper alloys are also well known for their conductivity, since the interaction between the two metals enhances overall performance.

How Processing Enhances Strength

When alloys are processed by either work hardening or age hardening, their strength increases. With work hardening, alloys get stronger as they are deformed. The more a metal is rolled, drawn, or bent, the harder it becomes. You’ve experienced this if you’ve ever bent a paper clip: easy the first time, not so much when you try to bend it back. However, if the material is heated, it will soften and regain its malleability.

With age hardening, the alloy is formed into its final shape and then heat‑treated. During the baking process, the alloy’s atoms move into their preferred, more stable arrangements through one or more mechanisms: forming new isolated phases (precipitation hardening), migrating to preferred locations within the crystal lattice (ordering), or separating into distinct phases (spinodal decomposition). These atomic rearrangements result in a significantly harder material.

There’s a common misconception that precious metals behave like steel. This is not the case. When steel is quenched, it cools rapidly and hardens. But with precious metals, the opposite is true — a high-temperature quench keeps the metal soft while preserving workability. In reality, precious metals have more in common with metals such as aluminum, copper, and titanium alloys than with steel. It’s worth noting that interactions within these alloys also depend heavily on their composition, and there are no simple universal rules.

Conclusion

Regardless of the application, the answer to “why alloy precious metals?” remains the same. Pure metals alone vary rarely posses it ideal combination of properties for a given application. Alloying elements are added to tune the final alloy’s properties to meeting the needs of a given application. When an alloy’s characteristics are matched to the needs of the application, electrical components will perform reliably and consistently.