Gold engineering alloys – the ultimate guide

Let’s talk about gold engineering alloys.

Gold has been one of the most revered precious metals from the birth of civilisation. As a symbol of wealth and power, it has been an obsession for mankind for centuries. From Egyptians to Persians to Romans – gold has been an integral part of every culture.

Why, then, would such a precious and expensive metal be used for something other than ornamental and decorative purposes?

The answer lies in its unique physical properties. Gold is highly malleable, is a very good conductor of electricity, does not tarnish easily, can be drawn into long wires with relative ease, and can be melted and made into different shapes. It gels well with other metals to make alloys. Its beautiful color and luster add to this long list of special properties which make it a sought-after metal.

Did you know? Almost 80 km (50 miles) of thin gold wire, ~5 microns in diameter, can be made from just one ounce of gold!

However, a major disadvantage of gold is that it is very soft. It is, therefore, combined with other metals like copper, platinum, nickel or silver to strengthen it. These gold alloys find a variety of applications in different industries.

Common Gold Alloys

Gold engineering alloys can take many forms, depending on the application they’re needed for. Here is a list of the most common ones in use today:

Gold and silver: Adding silver to gold lowers its melting point, and the resulting alloy is soft, ductile, malleable and homogenous. The appearance of the alloy varies from greenish-yellow (20-40% silver) to silver-white (>60% silver).

Gold and copper: This alloy is harder, more elastic and less malleable than gold, and appears reddish. Copper-gold alloys lose their lustre when exposed to air, as copper readily oxidises. (This oxidised coating can be removed by a process called blanching, which involves immersing the alloy in dilute acids.)

Gold and aluminium: This alloy has an intense colour, varying between yellowish green to a deep purple (~22% aluminium). The deep-purple alloy has a higher melting point than that of pure gold.

Gold and palladium: The addition of palladium to gold increases its strength, hardness, melting point and modulus of elasticity. This gold-palladium combination is called white gold.

Gold and titanium: Adding gold to titanium has recently been shown to improve the hardness of titanium – a 1:3 mixture of gold and titanium has been found to be 3-4 times harder than steel!

Golden dental crowns

Applications of gold engineering alloys

Gold engineering alloys are used in a wide range of products, some obvious, some not so obvious. Here’s an overview of some of the places you can find gold engineering alloys being used:

Ornaments: Adding copper to gold gives it a red tinge while adding silver, zinc or any other metal makes it paler in appearance. Gold-palladium alloy, also called white gold, is used extensively in jewellery making. Copper, platinum, silver, zinc, and nickel are also added to gold depending upon the kind of appearance needed for the jewellry.

Dentistry: Gold is chemically inert and is non-allergenic; two very important criteria for use in our mouths! Gold alloys are used in crowns, fillings, caps and other orthodontic applications.

Electronics: Electronic devices use low voltages and currents, and hence, any corrosion at the contact points affect their normal operation. Gold, being a very good conductor and resistant to corrosion, is used as an alloy or electroplated, for use in relay and switch contacts, connecting wires and joints. These are highly reliable and are used in cellphones, television sets, calculators, and GPS units.

Aerospace: Gold alloys are used in satellite components, circuitry, and spacesuits. Gold-coated polyester film reflects infrared rays and helps to maintain the temperature of the spacecraft.

High-frequency SMA connectors – Gold plated for high conductivity and stability

Healthcare: Artificial knee and hip joints traditionally use titanium as the primary material. However, recent discoveries have shown that adding gold to titanium greatly improves its strength, biocompatibility and wear-resistance. This alloy is further being researched for commercial use.

Medical uses: Radioactive isotopes of gold are used to treat certain cancers. Radioactive gold is also used in diagnosis, by injecting it in a colloidal solution and tracking it as it passes through the body. Gold alloys are also used in surgical instruments and life-support devices.

Gold engineering alloys in summary

Gold is one of the most expensive metals. However, its unique properties justify its high cost. As more versatile uses for gold alloys are being discovered, their demand will only grow in the years to come.

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