Properties of metals compared: density, melting point, stiffness

The four properties for every metal in this article

Which metal is the lightest, and which is the densest?

Among the materials compared here, magnesium AZ31B is the lightest, at 1.8 g/cm³, one rounded value on a supplier listing. Aluminium 6061 follows at 2.7 g/cm³ (typical value) and Ti-6Al-4V at 4.43 g/cm³, with no condition stated. Then come zirconium (6.51 to 6.64 g/cm³) and zinc (6.3 to 7.2 g/cm³); grey tin is lighter than both, but ordinary tin is not.

Gold and tungsten tie at the top. Gold is 19.3 g/cm³ (purity not stated); tungsten has three entries, from 19.25 to 19.3 g/cm³. The profiles carry too few digits to separate them. Below them come tantalum at 16.6 g/cm³, palladium at 12 g/cm³, lead at 11.3 g/cm³ and silver at 10.5 g/cm³ (bar, 99.95 % purity, 20 °C).

Ranges are conditions, not noise. Zinc spans pure zinc and die-cast alloys at zero porosity. Tin runs 5.77 to 7.31 g/cm³ because grey tin is included; its other entries run from 7.265 to 7.31 g/cm³. Steel 1018 shows 7.67 to 7.9 g/cm³ by form and source, 316 7.87 to 8.07 g/cm³ and Inconel 718 8.22 g/cm³.

Which metal has the highest melting point?

Among the materials compared here, tungsten melts highest, at 3,422 °C. Tantalum follows at 3,017 °C, molybdenum at 2,623 °C and niobium at 2,350 to 2,477 °C, which spans the pure metal and the C-103 alloy. No alloy in the set comes near them.

The engineering alloys sit much lower and melt over a range. Ti-6Al-4V melts at 1,604 to 1,660 °C, Inconel 718 at 1,260 to 1,336 °C and 316 at 1,375 to 1,440 °C. Steel 1018 shows 1,480 to 1,526 °C, Invar 36 1,427 °C and elemental nickel 1,455 °C. For an alloy, design to the solidus (the lower end). For niobium and zinc, whose bars span a pure metal and an alloy, use the value for your grade.

At the bottom, tin melts at 232 °C, lead at 328 °C and zinc at 375 to 420 °C. The light metals melt at 605 to 630 °C for AZ31B and 582 to 652 °C for 6061. Between them sit copper 1,083 to 1,085 °C, brass C36000 954 to 1,049 °C, bronze C95400 1,027 to 1,038 °C, silver 962 °C and gold 1,065 °C.

A melting point is not a use temperature. In the 316 profile, annealed plate has a yield strength that falls from 193 to 213 MPa at 295 K to 102 MPa at 922 K, while the melting range starts at 1,375 °C. Inconel 718 yield falls from 171 ksi to 133 ksi between room temperature and 1300 °F on the same bar.

Which metal is the stiffest?

Among the nineteen profiles with a charted modulus, tungsten is stiffest at 411 GPa (no temperature stated), 2 times the 205 GPa of 4140 steel. Brass C36000, zinc, molybdenum and silver are not charted (see the chart note), and no figure recorded for them would pass tungsten.

Below tungsten the data jumps to a cluster. Steel 1018 shows 190 to 210 GPa by processing, 316 190 to 205 GPa, nickel 205 GPa and Inconel 718 200 GPa at 70 °F; the Inconel table falls from 29 to 23 million psi by 1300 °F. Tantalum is 186 GPa, Invar 36 140 to 141 GPa and palladium 121 GPa. The light metals are less stiff: Ti-6Al-4V 114 GPa, aluminium 6061 68.9 GPa and AZ31B 45 GPa. Lead (16 GPa) is far below.

Per unit of density the picture flattens. Divide each profile's largest modulus by its largest density and AZ31B, 6061, Ti-6Al-4V and 4140 all land at 25 to 26 GPa per g/cm³. That fits parts loaded along their length. In bending, stiffness at equal mass depends on modulus divided by density cubed (general engineering knowledge, not in our data); on the numbers above that ranks AZ31B first, 6061 second, Ti-6Al-4V third and 4140 last. Titanium beats steel, but by far less than the other two light metals.

Which metal has the highest tensile strength?

Among the sixteen profiles that the chart reads, Inconel 718 shows the highest typical value at 1,386 MPa, one hot-rolled aged bar, not a specification minimum. Steel 4140 ranges 745 to 1,283 MPa; the top is a laboratory test in 69 MPa helium and the datasheet quenched-and-tempered rows are 850 to 930 MPa. Ti-6Al-4V annealed shows 900 to 1,000 MPa, against an AMS 4928 bar minimum of 931 MPa.

The middle mixes bases. 316 shows 480 to 620 MPa, with an ASTM A240 minimum of 515 MPa. Bronze C95400 is specified at 515 MPa to 655 MPa minimum by casting route and brass C36000 at 330 MPa to 480 MPa minimum across tempers. Zirconium spans 379 to 615 MPa, nickel 380 to 520 MPa for annealed rod, Invar 36 448 to 518 MPa and molybdenum 411 MPa from one laboratory rod.

At the weak end are steel 1018 at 430 to 440 MPa, niobium C-103 at 386 MPa minimum, soft copper at 179 to 262 MPa, zinc at 150 to 374 MPa, 6061 at 310 MPa and AZ31B at 290 MPa. Read the bars as bands, not as an order.

Seven profiles are not charted. Lead, tin, tungsten and tantalum hold no tensile strength. Silver holds 172 to 330 MPa (soft to hard bar), gold 135 to 342.7 MPa (wire) and palladium 280 MPa (annealed) under other property names. All are below Inconel 718, so the ranking stands, but they are different forms.

Which metal conducts heat best, and which worst?

Silver conducts heat best in the data: 429 W/(m·K) for 99.95 % bar at 0 to 100 °C, about 1.1 times the 391 W/(m·K) of oxygen-free copper C10200 at 20 °C. The temperatures differ, so the gap is indicative. Gold follows at 320 W/(m·K), then tungsten at 174 W/(m·K) and aluminium 6061 at 167 W/(m·K).

Alloying costs conduction. From oxygen-free copper the data falls to 116 W/(m·K) for brass C36000 and 58.7 W/(m·K) for bronze C95400, both at 20 °C. Zinc die-cast alloys show 109 to 115 W/(m·K) and AZ31B 96 W/(m·K). Palladium is 72 W/(m·K) and nickel 70.3 W/(m·K).

Titanium, Invar, Inconel and austenitic stainless carry heat poorly. Ti-6Al-4V is the lowest at 6.7 W/(m·K) at 20 °C, then Invar 36 10.5 W/(m·K), Inconel 718 11.4 W/(m·K) and 316 13 to 17 W/(m·K). Such a part holds large temperature differences (general engineering knowledge, not in our data).

What does a designer trade between metal families?

Light metals give up heat resistance: aluminium melts from 582 °C. The steels share a modulus near 200 GPa, so choose between 1018, 4140 and 316 on strength and corrosion. Copper alloys give up some conduction for strength and machinability. Inconel 718 is strong at heat but conducts poorly. Zinc, lead and tin trade strength for low melting points that suit casting and soldering. Silver and gold trade mass for conduction; palladium does not, at 72 W/(m·K). Cost is not in our data.

Invar 36 is chosen to hold a dimension, not for strength. Its profile gives mean expansion coefficients of 1.18 to 4.92 ppm per kelvin across sources and temperature ranges, the low values being close to room temperature.

Traps the numbers do not show. Magnesium: the profile notes fire risk from the metal and corrosion in chloride solutions; coupling it to aluminium or steel in a wet joint invites galvanic attack (general engineering knowledge, not in our data). Tin: below 13.2 °C white tin can change to grey tin (tin pest), the same grey form that sets the low end of the density bar. Lead: a reproductive toxicant, limited to 0.1 % in most new EU electronics, and it creeps at room temperature, so its modulus does not describe sustained loading. Leaded brass C36000 holds 2.5 to 3.0 % lead and sits outside California's 0.25 % lead-free plumbing limit.

Terms used

Density

mass per unit volume, here in g/cm³. Alloy, form and porosity change it.

Solidus and liquidus

the temperatures where an alloy starts to melt and where it is fully liquid.

Elastic modulus

Young's modulus: how stiff a metal is in the elastic range. Higher is stiffer. It is not strength.

Ultimate tensile strength

the highest stress a metal carries in a tensile test before it necks and breaks.

Thermal conductivity

how fast heat flows through a metal, in W/(m·K). A higher number moves heat faster.

Temper and annealed

the state set by working and heat treatment. Annealed metal is soft; harder tempers are stronger.

Minimum against typical value

a minimum is what a specification guarantees. A typical value is a measured average, often higher, with no guarantee.

Refractory metal

a metal with a very high melting point, such as tungsten, tantalum, molybdenum and niobium (general engineering knowledge, not in our data).

What to check before you order

1. Ask for the grade, form, temper or heat treatment and temperature behind every number, and whether it is a minimum or a typical value.
2. For melting, ask for the solidus as well as the liquidus, and for strength at your operating temperature, not at room temperature.
3. For stiffness, ask whether the modulus is static or dynamic and at what temperature. The profiles often do not say.
4. For 6061, ask for the certified T6 minimum, since the value here is typical and marked not for design. For 4140, ask for the heat treatment, since the top of its range is a laboratory test. For die castings, ask for density at the actual porosity.
5. For heat flow, ask for conductivity at your operating temperature and in the grade you will buy.
6. For magnesium, tin, lead and leaded brass, check coating and coupling, cold storage, and the lead rules for your market.

What do we not know yet?

• Four profiles are not charted for elastic modulus: brass C36000 (the supplier printed a value with an apparent units error, so none was recorded), zinc, molybdenum (329 GPa appears in its profile notes but was not recorded) and silver (a Goodfellow tensile modulus of 82.7 GPa under another property name). No stiffness ranking covers them.
• Lead, tin, tungsten and tantalum hold no tensile strength; the lead and tin profiles say none was found in any opened source, and the tungsten profile repeats only a qualitative claim. Silver, gold and palladium hold bar, wire or annealed figures that the chart does not read.
• Steel 4140 holds no melting point. Strength at temperature appears in only some profiles (for example 316, Inconel 718, niobium C-103 and Zr 702), so no strength ranking at temperature is possible.
• Electrical conductivity is stored in MS/m, %IACS and S/m, and not at all for several of these metals, so it is not charted. Thermal expansion is held by most profiles but only Invar 36 is discussed.
• Cost, corrosion rates and fatigue are not compared, and the article covers only the profiles listed, not every grade in each family.

Questions people ask