Alloy

An alloy is a combination of metals or of metals and other elements.

Examples

Vanadium steel

Used in early Ford’s.

Crown gold

A 22 karat (kt) (916 ²⁄₃ fine) gold alloy used for English & UK gold coins from 1526 (Henry VIII) to 1914 (as currency), and since then for trade and bullion coins. (‌²²⁄₂₄ gold, ‌²⁄₂₄ copper)

𝜌 = 17.61 g/㎝³

“Standard gold” (US)

A 900 fine gold alloy used for US coins. (90% gold, ≤5% silver, 5-10% copper)

𝜌 = 17.43±.12 g/㎝³

“Crown electrum” (d20)

A 4 ℥ 17 ³⁄₄ ʤ gold, 6 ℥ 3½ ʤ silver, 18 ³⁄₄ ʤ copper alloy worth ‌¹⁄₂ of crown gold by weight (presuming that sterling silver is worth ‌¹⁄₁₀ of crown gold by weight). (i.e. the d20 gold-silver standard)

Britannia silver

An 11 ℥ 10 ʤ (958 fine) silver alloy required in England for “wrought plate” (non-monetary silversmithing) from 1697–1720 to inhibit coin clipping and melting. (‌²³⁄₂₄ silver, ‌¹⁄₂₄ copper)

𝜌 = 10.42 g/㎝³

Sterling silver

An 11 ℥ 2 ¹⁄₄ ʤ (926 fine) fine silver alloy used for English & UK silver coins from before 1158 (Henry II) to 1919. (92.6% silver, 7.4% copper)

𝜌 = 10.37 g/㎝³

“Standard silver” (US)

A 900 fine silver alloy used for US coins from ____ to 1964. (90% silver, 10% copper)

𝜌 = 10.32 g/㎝³

“Coin gold” (d20)	906 fine gold	‌29⁄32 gold, ‌3⁄32 copper	𝜌 = 17.42
“Coin electrum” (d20)	906 fine electrum	‌25⁄64 Au, ‌33⁄64 Ag, ‌3⁄32 Cu	𝜌 = 12.53
“Coin silver” (d20)	906 fine silver	‌29⁄32 silver, ‌3⁄32 copper	𝜌 = 10.33
“Coin copper” (d20)	906 fine copper	‌29⁄32 copper, ‌3⁄32 tin/zinc	𝜌 = 8.76

1700's katana steel 𝜌 = 7.74

1500's katana steel 𝜌 = 7.76

Alloy steel, AISI 5160 (UNS G51600)^AZO

97.45% iron, 0.6% carbon, 0.8% chromium, 0.87% manganese, 0.22% silicon, 0.03% phosphorus, 0.03% sulfur.

𝜌 = 7.85

Tool Steel, A2 (UNS T30102)^AZO

90.28% iron, 1% carbon, 5.13% chromium, 1% manganese, 0.5% silicon, 0.3% nickel, 1.15% molybdenum, 0.33% vanadium, 0.25% copper, 0.03% phosphorus, 0.03% sulfur.

𝜌 = 7.86

Density

ᴍ = material constituent

𝜌 = density (i.e. g/㎝³)

𝐴ᵣ = atomic weight

𝑤 = mass fraction (i.e. ‌⁹⁄₁₀, .900 or 90%)

𝑎𝑡٪ = atomic percent

Alloy (general)

𝜌Alloy	=	1
		𝑤ᴍ₁ 𝜌ᴍ₁ + 𝑤ᴍ₂ 𝜌ᴍ₂ + 𝑤ᴍ₃ 𝜌ᴍ₃ + ⋯

Au-Ag

𝜌_Au-Ag = 𝜌Au 𝑤Au + 𝜌Ag 𝑤Ag − 4 exp(0.005 𝑤Au) 𝑤Au 𝑤Ag

Au-Cu

𝜌_Au-Cu = 𝜌Au 𝑤Au + 𝜌Cu 𝑤Cu − 5 exp(0.01 𝑤Au) 𝑤Au 𝑤Cu

Ag-Cu

𝜌_Ag-Cu = 𝜌Ag 𝑤Ag + 𝜌Cu 𝑤Cu − 0.12 exp(0.02 𝑤Cu) 𝑤Ag 𝑤Cu

Au-Ag-Cu

𝜌_Au-Ag-Cu = 1.004 𝑎𝑡٪Au 𝜌Au + 1.03 𝑎𝑡٪Ag 𝜌Ag + 0.096 𝑎𝑡٪Cu 𝜌Cu + x − y

x = 0.35 ( cos(45+0.45 𝑎𝑡٪Au) + cos(45+0.45 𝑎𝑡٪Ag) + sin(𝑎𝑡٪Au) )

y = 0.005 (𝑎𝑡٪Au+𝑎𝑡٪Ag) cos(0.9 𝑎𝑡٪Cu) + 0.2 cos(3.2 𝑎𝑡٪Cu)

𝑎𝑡٪ᴍ₁	=	𝑤ᴍ₁ 𝐴ᵣᴍ₁
		𝑤ᴍ₁ 𝐴ᵣᴍ₁ + 𝑤ᴍ₂ 𝐴ᵣᴍ₂ + 𝑤ᴍ₃ 𝐴ᵣᴍ₃ + ⋯

Hardness

1812	Hᴍ	Hardness, Mohs
1900	Hʙ	Hardness, Brinell
1908	Hʏ	Hardness, Meyer
1908	Hʀ	Hardness, Rockwell
1921	Hᴠ	Hardness, Vickers
1939	Hᴋ	Hardness, Knoop
1975	Hʟ	Hardness, Leeb
2000	Hᴅ	Hardness, D&D/d20	≈ Hᴍ × 2

Check for accuracy

Hʙ = Hᴠ ÷ 1.05 + 10

Hᴠ = Hʙ × 1.05 − 10.5

References

• Kraut, J.C.; Stern, W.B. (June 2000) “The Density of Gold-Silver-Copper Alloys and its Calculation from the Chemical Composition”. Gold Bulletin, Vol. 33, Iss. 2, pp. 52–55. Springer-Verlag. doi:https://doi.org/10.1007/BF03216580.
• Good, David; Cabri, Louis J.; Ames, Doreen E. (April 2017) “PGM Facies variations for Cu-PGE deposits in the Coldwell Alkaline Complex, Ontario, Canada”. Ore Geology Reviews, Iss. 90. doi:10.1016/j.oregeorev.2017.04.028.

aurian silver (<50 at% Ag) – i.e. “Egyptian silver” derived from silver-rich alluvial gold deposits and alloyed with as much as 15% copper.

electrum (50–80 at% Ag)

gold (>80 at% Ag)