Gold Alloys
Gold is the one common metal that forms no oxide or sulfide at all, so a gold surface conducts as well after decades in air as on the day it was made — about 70 % of the conductivity of copper. Pure 24K is 19.3 g/cm³, melts at 1,064 °C and is very soft (around 25 HV). Alloying with silver, copper, palladium or nickel raises hardness to 150–250 HV in 18K and 14K, sets the colour (yellow, rose, white) and lets some alloys age-harden. The same chemistry runs through the karat jewelry alloys, the dental golds, the BAu brazing fillers and the hard-gold contact alloys.
Popular gold grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Gold 24K | 30 | 125 | 19.32 | Fair | Excellent | Contacts, bond wire, IR mirrors |
| Gold 18K | 200 | 450 | 15.5 | Good | Excellent | Fine jewelry and dental restorations |
| Gold 14K | 200 | 400 | 13.07 | Good | Very good | Durable jewelry, watch cases, clasps |
| 18K White Gold | 300 | 520 | 15.8 | Good | Very good | White jewelry alloy, usually rhodium-plated |
| 22K | 75 | 220 | 17.8 | Fair | Excellent | High-purity soft jewelry alloy |
| BAu-4 | 210 | 340 | 15.9 | Fair | Fair | Vacuum brazing of superalloys and stainless |
| Dental Gold Type III | 250 | 420 | 15.6 | Good | Very good | Crowns and bridges; the dental standard |
Choose gold for
Electrical contacts, connectors, slip rings and bond wire that must stay clean at signal voltages for decades; hard-gold plating on copper-alloy springs; infrared mirrors and thermal-control coatings; dental crowns, inlays and frameworks; fine jewelry and watch cases; and brazed joints in turbine and vacuum assemblies where a nickel-bearing gold filler wets superalloys without eroding them.
Look elsewhere when
A plating delivers the property — which is nearly always: 0.5–1.5 µm of hard gold over nickel on a C17200 or C51000 spring does what a solid part would; strength or hardness matters (even Gold 14K is weaker than mild steel); the contact carries real current, where Silver 999 or a silver-tin-oxide alloy conducts better and costs far less; or a white, hard, hypoallergenic jewelry metal is wanted, where Pt950 or Pd950 does not need rhodium plating to stay white.
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Gold by application
- Contacts and connectors
- Gold 24K wire and foil for bond wire and reference contacts; the cobalt- and nickel-hardened contact golds AuCo5 and AuNi5 for sliding contacts and slip rings that would wear through soft gold.
- Jewelry and watch parts
- Gold 18K for colour and value, Gold 14K for hardness and price, 18K Rose Gold and 18K White Gold for colour variants; cast to shape, CNC-machined or die-struck and hand-finished.
- Dental restorations
- Dental Gold Type I and Type II for soft inlays, Dental Gold Type III for crowns and bridges, Dental Gold Type IV for partial-denture frameworks that need an age-hardened 200 HV or more.
- Brazing fillers
- BAu-4 (950 °C) for stainless and nickel superalloys in vacuum and furnace brazing; BAu-2 and BAu-3 gold-copper fillers for electronic and vacuum-tube joints; the BVAu grades where volatile impurities must be below vacuum-tube limits.
Working with gold
- Casting
- Investment (lost-wax) casting from printed or milled patterns is the standard route for jewelry and dental parts in every karat; gold alloys cast cleanly with little gas porosity. Every gram of sprue, flash and grinding dust is recovered — on a gold job the scrap is worth more than the labour.
- Machining
- Gold 24K smears and clogs the tool; Gold 14K and Gold 18K machine like a soft brass with sharp polished tools, high speed and light cuts. Parts are machined slightly oversize and finished by hand. Full chip recovery is mandatory, and the weight in and out is reconciled on every job.
- Joining and plating
- Hard-solder with matched-karat fillers, laser-weld for repair and thin sections, wire-bond for electronics. Engineering gold is almost always electroplated: 0.1–1.5 µm hard gold (cobalt- or nickel-hardened) over a nickel barrier on copper-alloy contacts, specified by thickness, hardness and underplate rather than by "gold plated".
Other precious metal series
Gold Alloys — frequently asked
What is gold?
Gold is the one common metal that forms no oxide or sulfide at all, so a gold surface conducts as well after decades in air as on the day it was made — about 70 % of the conductivity of copper. Pure 24K is 19.3 g/cm³, melts at 1,064 °C and is very soft (around 25 HV). Alloying with silver, copper, palladium or nickel raises hardness to 150–250 HV in 18K and 14K, sets the colour (yellow, rose, white) and lets some alloys age-harden. The same chemistry runs through the karat jewelry alloys, the dental golds, the BAu brazing fillers and the hard-gold contact alloys.
Which grade of gold should I use?
Gold 24K for anything where the surface chemistry is the point: contacts, bond wire, IR mirrors, plating anodes — and nothing structural. Gold 18K for fine jewelry and porcelain-bonded dental work: 75 % gold, good colour, about 150 HV annealed and harder with cold work. Gold 14K when a piece must survive daily wear or take a thread or a spring: 58.5 % gold, 170–250 HV, the working alloy for rings, watch cases and clasps. 18K White Gold is nickel- or palladium-whitened; the nickel version is hard and springy but a common allergen, the palladium version soft and hypoallergenic, and both are usually rhodium-plated. 22K and 24K jewelry is soft and scratches; 9K and 10K are the legal minimums in the UK and US. BAu-4 (82Au-18Ni) is the vacuum-brazing filler for superalloys and stainless; Dental Gold Type III is the crown-and-bridge standard, Dental Gold Type IV the hard, age-hardenable partial-denture alloy.
Which grade of gold is the strongest?
AuCo5 has the highest yield strength in the series at 650 MPa; AuNi follows at 620 MPa. Values are for each grade's default condition.
Which grade of gold is easiest to machine?
Dental Gold Type II (machinability good, 65/100), then Dental Gold Type III (60/100).
18K or 14K for a part that must last?
14K. It is 58.5 % gold, about 170–250 HV depending on cold work and ageing, and resists scratching, bending and wear far better than 18K at 150 HV — which is why rings, watch cases, clasps and hinges are made in it. 18K gives a richer colour and slightly better tarnish resistance in rose and yellow alloys, and it is the fine-jewelry and dental standard; where the part is a thin section that takes load, 14K is the engineering choice.
Why is white gold rhodium-plated?
Because no white-gold alloy is truly white. Nickel-whitened 18K White Gold is pale yellow-gray and hard; palladium-whitened versions are grayer and softer. A 0.5–1 µm rhodium flash gives the bright white, hard, tarnish-free surface customers expect, and it wears through in a few years on a ring. Pt950 and Pd950 are white all the way through and do not need it.