How do I choose the right material for my metal fabrication project?

The short answer

Start with the environment, not the datasheet

Almost every material decision that goes wrong goes wrong in this order: someone picks steel for strength, then discovers the part lives outdoors, then adds a coating, then discovers the coating cannot survive the weld heat. Working the other way round resolves most parts in two questions. Where will the part be, and what load does it actually carry?

Once those are fixed, the material list usually collapses to two candidates, and the remaining questions - forming, finish and volume - decide between them rather than opening the field again.

The five families, and the numbers that separate them

Density, tensile strength and cost index are the three figures worth comparing. Note that cost per kilogram is not cost per part: aluminium is roughly three times the price of galvanised steel per kilogram but only a third of the density, so a part sized by stiffness rather than by strength can come out close to even.

What each family actually costs

Indicative 2026 prices sit at roughly USD 1.20 to 1.80 per kilogram for cold-rolled steel, 1.40 to 2.00 for galvanised, 4.50 to 6.50 for 5052 aluminium, 3.50 to 5.50 for 304 stainless and 5.00 to 7.50 for 316. The chart below turns that into a relative index so the gaps are visible at a glance.

Two levers move the material line on a quote more than the price per kilogram does. The first is scrap: nesting efficiency leaves 15 to 35 percent of the sheet unused depending on part shape, so a design that nests well beats a cheaper alloy. The second is thickness, because material cost scales linearly with it - dropping a 2.0 mm part to 1.5 mm cuts material cost by roughly a quarter if the load case still closes.

On substitution, the biggest single saving available is replacing 304 stainless with galvanised steel on a part that does not need corrosion performance. That is worth 60 to 70 percent of the material cost. It is also the substitution most likely to be regretted, so it belongs in a drawing note rather than in a purchasing decision.

Strength, weight and corrosion: three trade-offs

Cold-rolled low-carbon steel forms easily, welds predictably and costs least, but it has no corrosion resistance of its own, so it either gets coated or it gets galvanised. Galvanised sheet carries a zinc barrier that protects scratches by sacrificial action, which is why it is the default for outdoor enclosures and ducts; the cost is that the coating boils at welding temperature, so galvanised assemblies are often riveted or clinched instead.

Stainless works the opposite way. Austenitic grades are strong - 515 to 620 MPa against 270 to 410 MPa for mild steel - and resist corrosion through a chromium oxide layer that repairs itself in air. The practical distinction is 304 against 316: 316 adds molybdenum and is the grade for chlorides, so marine and chemical service, while 304 covers indoor and mildly corrosive work. Both work-harden, which is why stainless springs back more than mild steel and needs more press force or a larger bend radius.

Aluminium is chosen for mass rather than strength. 5052 is the fabrication grade because it bends well and resists marine air; 6061-T6 is roughly twice as strong but cracks if formed on a tight radius, so a part that needs both strength and bends is usually designed as 6061 with the tight radii relieved, or formed in 5052 and heat-treated afterwards. Copper C1100 and brass C260 are reserved for conductivity, thermal performance and appearance.

Choosing in four questions

Run these in order. In practice questions one and two close most decisions, and the last two only confirm them.

Seven substitutions that cost more than they save

• 6061-T6 in place of 5052 on a formed part. The strength gain is real, and the bend cracking is more real.
• Copper or brass in contact with aluminium. In a wet environment the joint becomes a galvanic cell. Insulate the interface or pick one family.
• Uncoated steel outdoors. Cold-rolled steel without a coating is a maintenance item, not a finished part.
• Ignoring rolling direction. Bending across the rolling direction carries a far lower cracking risk than bending parallel to it.
• Forgetting that coatings add thickness. Anodising, plating and powder coating change dimensions, which matters on threads and press fits.
• Thickness chosen before the material. Aluminium needs more thickness than steel for the same stiffness, so copying a steel thickness onto aluminium loses stiffness rather than saving weight.
• Stainless specified for looks alone. A brushed 304 panel is roughly four times the material cost of a painted steel panel with the same geometry.

Material review at SOMI Custom Parts

We hold carbon steel, galvanised steel, 301 / 304 / 316 stainless, 5052 and 6061 aluminium, copper and brass in the thicknesses our laser, bending, stamping and welding equipment runs, and we will say when a substitution changes the process rather than only the price. Send a drawing and an annual quantity: see sheet metal fabrication, metal stamping, or start with our inquiry form.