Strongest lightweight metals: titanium, aluminium, steel, magnesium

At a glance

Which metal gives the most strength for the least mass?

Our data shows that Ti-6Al-4V gives the most yield strength for its mass, but only at its peak. Solution treated and aged, it reaches 1,100 MPa at 4.43 g/cm³, which is 248 MPa per g/cm³, and it is the point with the steepest line from the origin. Read the chart as strength divided by density: the higher and further left a point sits, the better the trade.

Each profile at its highest yield strength gives these figures: Titanium alloy Ti-6Al-4V ELI (Grade 23) 205 MPa per g/cm³, Titanium Grade 9, Ti-3Al-2.5V (UNS R56320) 192 MPa per g/cm³, Aluminium-lithium alloy 2195 188 MPa per g/cm³, Aluminium alloy 7075-T6 180 MPa per g/cm³, Alloy steel AISI 4130 169 MPa per g/cm³ and 17-4 PH stainless steel 161 MPa per g/cm³. Annealed, the usual purchase, Ti-6Al-4V gives 830 to 950 MPa. The bottom of that range is level with Aluminium-lithium alloy 2195 and only slightly above Aluminium alloy 7075-T6, so the lead is real only at the aged peak. The top of the Titanium alloy Ti-6Al-4V ELI (Grade 23) range is a research forging and the top of the Titanium Grade 9, Ti-3Al-2.5V (UNS R56320) range is cold-worked tube, so their order depends on the condition you buy.

The steels reach the highest absolute strength: Alloy steel AISI 4130 up to 1,330 MPa and 17-4 PH stainless steel up to 1,262 MPa, at about 2.8 times the density of Aluminium alloy 7075-T6. The 4130 maximum comes from a laboratory hydrogen study. Commercial AMS 6346 bar in the same profile is 100 ksi (a little under 700 MPa) yield, and at that level steel falls further behind.

Alloy steel AISI 4340 and Inconel 718 rank lower still; Inconel 718 is the densest metal here, at 8.22 g/cm³, and is chosen for heat, not for mass. Commercially pure titanium, Grade 2 (UNS R50400), Aluminium alloy 6061 and Aluminium alloy 2024 rank lowest on strength per mass. Aluminium alloy 6061 is still the usual weldable, easily sourced aluminium (general engineering knowledge, not in our data), so a low rank does not make it a poor choice for the right job.

Treat the chart as a screen, not a spec. Yield strength is not the only limit: fatigue, fracture toughness and buckling often decide titanium against 7075, and our data does not compare them across these metals. A real pick needs the temper, the product form and the supplier's guaranteed minimum.

How much does temper change how strong each metal is?

Temper moves strength a long way within one alloy. Alloy steel AISI 4130 spans 435 to 1,330 MPa in our data, 17-4 PH stainless steel spans 725 to 1,262 MPa, and Ti-6Al-4V spans 830 to 1,100 MPa. A chart with one number per alloy would hide that spread, which is why the bars run from low to high.

For Ti-6Al-4V, the profile gives 830 to 950 MPa annealed and 1000 to 1100 MPa solution treated and aged. The aged condition costs ductility: the profile gives 6 to 10 % elongation. For 17-4 PH stainless steel the aging temperature sets the strength. H900 is the strongest and hardest condition, and H1150 is softer and tougher.

For Alloy steel AISI 4340 the trade is explicit, and every value is a minimum for a named condition. The minimum Charpy impact energy is 42 J at condition U, where the minimum yield strength is 740 MPa. It falls to 9 J at condition Z, where the minimum yield strength is 1125 MPa for a 30 mm section. Those minimums run from 665 MPa to 1125 MPa across conditions, so 1125 MPa is not the grade minimum. More strength brings less toughness.

The aluminium profiles are mostly single typical values. Aluminium alloy 7075-T6 is a T6 tube figure, Aluminium alloy 6061 is a typical value that its datasheet marks not for design, and Aluminium alloy 2024 mixes a typical T4 figure with a forged lower bound. Do not compare a typical aluminium value directly with a steel minimum. Ask each supplier for the guaranteed figure in the temper and form you will buy.

Is magnesium stronger than aluminium for its mass?

Our data cannot say for yield strength, because the Magnesium alloy AZ31B profile holds none. It lists a density of 1.8 g/cm³, the lowest in this set, and a tensile strength of 290 MPa for an as-rolled foil and sheet listing.

On tensile strength per mass, AZ31B gives 161 MPa per g/cm³, against 115 MPa per g/cm³ for Aluminium alloy 6061, 169 MPa per g/cm³ for typical Aluminium alloy 2024 and 204 MPa per g/cm³ for Aluminium alloy 7075-T6. That puts magnesium above 6061, just below 2024 and below 7075. It is a rough reading, because the magnesium figure is one as-rolled listing and the aluminium figures are typical values for other tempers. Yield strength usually limits a design, and magnesium alloys typically have a lower yield-to-tensile ratio than aluminium alloys (general engineering knowledge, not in our data), so the tensile ordering flatters magnesium.

Magnesium also pays in other properties. Its stiffness is 45 GPa, or 0.6 times that of Aluminium alloy 7075-T6. The profile cites a study of H24 sheet in which yield and maximum stress were lower along the rolling direction than across it, and fell as test temperature rose. Magnesium metal also carries fire and flammable-gas hazard statements.

Corrosion is the largest cost. Uncoated AZ31 corroded at 9.7 mm/year in 5 M NaCl and at 0.27 mm/year in 3.5 % NaCl, both in 14-day immersion tests at 37 °C. These are short tests expressed as yearly rates, not service lives, and the profile notes the test alloy was AZ31, not AZ31B. In one intermittent 5 M test, soft-sparking coatings cut the rate from 7.8 mm/year uncoated to about 0.30 (PF) and 0.25 (PFS), which the paper calls more than 30 times lower; the PF figure alone is a little under that. This makes magnesium a choice for dry or coated parts where mass is the only goal.

What does a lighter metal cost in stiffness?

A lighter metal is almost always a less stiff one, and in our data the loss in modulus tracks the density saving closely. Compared with Aluminium alloy 7075-T6, Alloy steel AISI 4130 is 2.9 times as stiff and 2.8 times as dense. Ti-6Al-4V is 1.6 times as stiff and 1.6 times as dense. Magnesium alloy AZ31B is 0.6 times as stiff and 0.6 times as dense.

What that means depends on the load, and this part is general engineering knowledge, not in our data. For a bar loaded along its axis, in tension or compression, those matching ratios mean a swap of metal gives little extra stiffness per kilogram. For a plate or a beam in bending, the picture changes: a lighter metal can be made thicker for the same mass, and the thicker section is much stiffer. So bending-limited parts do favour low-density metals such as aluminium and magnesium. Check the right design index for your load case.

Heat treatment does not change stiffness much. The 17-4 PH stainless steel profile prints one modulus for all conditions, and the Alloy steel AISI 4340 profile gives one modulus range that is not split by condition. A part that deflects too much in an annealed condition will deflect about as much after you raise the yield strength.

Titanium sits in the middle. Titanium Grade 9, Ti-3Al-2.5V (UNS R56320) carries three modulus values from three listings. Titanium alloy Ti-6Al-4V ELI (Grade 23) gives 107 to 122 GPa at 20 °C and 95 to 111 GPa at 230 °C, so stiffness also falls as titanium warms. Ask the supplier which value applies to the product form before using it in a deflection calculation.

How hot can lightweight metals work?

Among the lightweight options, only Ti-6Al-4V has a temperature figure in our data: its profile cites a service limit of about 400 °C from a general reference, not a datasheet, so treat it as a rough guide. The aluminium and magnesium profiles hold no service temperature. The melting chart shows Aluminium alloy 7075-T6 melting at 532 to 635 °C and Magnesium alloy AZ31B at 605 to 630 °C, but both lose strength long before they melt (general engineering knowledge, not in our data), so ask for strength at your operating temperature. A study of H24 magnesium sheet found yield and maximum stress fell as the test temperature rose from room temperature to 400 °C.

The heavier alloys supply the hot-service data. Inconel 718 lists 704 °C as the use range stated in its datasheet, and 17-4 PH stainless steel lists 316 °C as the temperature to which high strength is maintained. These are different kinds of limit, so do not rank the two by those numbers.

Cold service is a different case. The Inconel 718 datasheet gives a higher tensile strength in a cold test (printed as -320 F) than at room temperature, and friction stir welds in Aluminium-lithium alloy 2195 plate gained a factor of 1.6 at cryogenic temperature. The Titanium alloy Ti-6Al-4V ELI (Grade 23) research forging gained tensile strength when cold, but its fracture toughness fell from 57.5 to 42.9 MPa√m at 77 K, so strength and toughness do not always move together.

What are the corrosion, welding and supply catches?

Each family pays for its strength per mass in a different way. Titanium costs you galvanic care, crevice attack in hot oxygen-poor seawater and a concentrated supply chain. Aluminium costs you cracking and galvanic attack. Magnesium costs you chloride corrosion. These notes come from profile text and are mostly supplier statements or single studies, not matched corrosion tests.

Titanium: suppliers state strong seawater and chloride resistance for Commercially pure titanium, Grade 2 (UNS R50400) and Titanium Grade 9, Ti-3Al-2.5V (UNS R56320). Our Ti-6Al-4V profile has only a general titanium statement and a supplier note, and no chloride pitting or crevice data. Ti-6Al-4V is widely used in seawater service (general engineering knowledge, not in our data), so treat this as a gap in our data, not a warning against it. A study in the Commercially pure titanium, Grade 2 (UNS R50400) profile found crevice corrosion for Grade 2 at 80 °C and for Grade 5 (which is Ti-6Al-4V) at 200 °C in near-anaerobic seawater. Titanium is near the noble end of the galvanic series, so it can speed corrosion of a less noble metal it touches.

Aluminium: Aluminium alloy 6061 resists air well but suffers galvanic attack when coupled to more noble metals in salt water. Aluminium alloy 7075-T6 is attacked in industrial and marine environments, and its T6 temper is susceptible to stress-corrosion cracking in the short-transverse direction; the profile reports better resistance in T73, and the 1981 NASA seacoast test recorded in the Aluminium alloy 2024 profile also found 7075-T651 highly susceptible. Aluminium alloy 2024 in T351 temper failed after very short exposure in a NASA stress-corrosion test of stressed short-transverse specimens at a seacoast site. Aluminium-lithium alloy 2195 is rated poorly by one supplier; in a salt test it pitted at the edges of fusion welds, and friction stir welds resisted pitting better.

Steels: the Alloy steel AISI 4340 profile holds no corrosion data. In Alloy steel AISI 4130, salt solution cut fatigue life at every strength level tested, and hydrogen gas lowered the threshold stress intensity as pressure rose, a case of hydrogen embrittlement. 17-4 PH stainless steel is rated Restricted for sea water on one supplier scale, and peak-aged material is more susceptible to stress-corrosion cracking.

Welding differs by family. Commercially pure titanium, Grade 2 (UNS R50400) welds well and Ti-6Al-4V is rated fair. Aluminium-lithium alloy 2195 hot-cracks in fusion welds, which is why friction stir welding was adopted. Alloy steel AISI 4130 is prone to hydrogen cracking in welds unless preheated. Multipass welds in 17-4 PH stainless steel must be solution annealed before aging.

Supply and price are only partly covered. The Ti-6Al-4V profile computes China at 70.3 % of world titanium sponge production in 2025 from USGS tonnage, and records that the United States produced no titanium sponge in 2025. The Magnesium alloy AZ31B profile puts China at 87.7 % of world primary magnesium production. Price per kilogram is not in the database, so this article cannot say what any of these metals costs.

Terms used

Yield strength

the stress at which a metal starts to deform for good. Below it, the part springs back when the load is removed.

Tensile strength

the highest stress a metal carries before it breaks. It is always at or above the yield strength.

Strength per mass

yield or tensile strength divided by density, often called specific strength. On a chart of strength against density it is the steepness of the line from the origin to a point.

Elastic modulus

a measure of stiffness: how much a metal stretches or bends under a given load. A higher value means a stiffer part.

Temper

a code for the heat treatment and working a metal was given. The same alloy can have very different strength in different tempers.

Solution treated and aged

a two-step heat treatment that raises strength by forming fine particles inside the metal, usually at some cost in ductility.

Stress-corrosion cracking

cracking that needs a tensile stress and a corrosive environment together. It can happen at stresses well below the yield strength.

Galvanic corrosion

extra attack on the less noble of two different metals that touch in a conductive liquid such as salt water.

Hydrogen embrittlement

loss of toughness when hydrogen enters a metal, which lets cracks grow at lower loads than in clean conditions.

What to check before you order

1. Ask for the temper, product form and section thickness behind every strength value, and for the guaranteed minimum rather than the typical figure.
2. For Ti-6Al-4V, ask for the section size over which the aged strength is guaranteed. The profile does not state the form for the aged values; only the AMS 4928 minimums are for bar.
3. For Alloy steel AISI 4340, ask for the ruling section of each quoted condition, because the minimum yield strength depends on it.
4. For aluminium 7075 and 2024, ask about grain direction and stress-corrosion rating, and whether the part is loaded across the short transverse direction. Ask for T73 where cracking matters.
5. For titanium, name the grade and the governing specification, including the oxygen and interstitial limits, and ask for the mill certificate.
6. Ask for fatigue and fracture-toughness data for the form and temper, since these often decide titanium against 7075 and are not compared in our data. Check buckling for thin light sections, minimum gauge and denting for aluminium and magnesium, and galling for titanium (general engineering knowledge, not in our data).
7. State the operating temperature and ask for yield strength at that temperature, not at room temperature.
8. List every metal the part will touch and the environment it will sit in, then ask for a galvanic compatibility and coating plan.
9. For steels above moderate strength, ask about hydrogen exposure, hydrogen baking after plating, and the post-weld heat treatment. For welded parts, name the process and ask for weld-joint strength, not base-metal strength.
10. Ask for the safety data sheet for the exact product, since titanium powder and swarf and magnesium metal carry fire hazard statements.

What do we not know yet?

• Magnesium: the Magnesium alloy AZ31B profile has no yield strength and no O or H24 temper strength, so magnesium cannot be placed on the main strength-per-mass chart.
• Design values: almost all strengths here are typical figures or supplier minimums, not design allowables from a handbook, and they mix tempers and product forms. Fatigue and fracture toughness are held for only a few profiles, so they are not compared.
• Temperature: service temperature is held only for Inconel 718 (a datasheet use range) and 17-4 PH stainless steel (high strength maintained to), on different bases, and there is no matched elevated-temperature yield strength for aluminium, magnesium or titanium.
• Thermal conductivity is held at different temperatures across profiles (for example Alloy steel AISI 4130 at two temperatures), so it is not compared in the glance table.
• Cost per kilogram, machining cost and lead time are not in the database, and corrosion data is mostly qualitative supplier statements apart from the magnesium rates.

Questions people ask