Which steel, stainless and aluminium grades are used in sheet metal fabrication?
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- Issue Time
- Nov 25,2024
The short answer
Common sheet metal grades are cold-rolled SPCC or Q235 carbon steel, SGCC galvanised steel, 304 and 316 stainless, 5052-H32 and 6061-T6 aluminium, and copper or brass. Thickness runs about 0.5 to 6 mm, and grade choice is driven by corrosion, formability, weight and weldability rather than price alone.
Specify the decimal thickness, not the gauge
The single most common specification error in sheet metal is quoting a gauge number without the metal. A 16 gauge sheet is 1.52 mm in carbon steel, 1.59 mm in stainless, 1.29 mm in aluminium and 1.61 mm in galvanised steel. The same word describes four different thicknesses, and the price follows the metal rather than the number. Gauges also run backwards: 26 gauge is thinner than 16 gauge, because the numbering dates from wire drawing. On a drawing the safe habit is to write the material grade and the decimal thickness together, and to treat the gauge as a shop reference only.
Thickness matters more than most buyers expect because it feeds straight into forming. A variation of 0.075 mm inside one sheet is enough to move a bend angle and change the required press-brake pressure, so a coil with a loose thickness tolerance produces a batch of parts that vary from one end to the other. Where a part is formed and then assembled, the thickness tolerance is effectively part of the dimensional tolerance, and it should be agreed with the material supplier rather than discovered on the press.
Carbon and galvanised steel: the default and the outdoor variant
Cold-rolled carbon steel, sold as SPCC in the Japanese convention and as DC01 in the European one, is the workhorse of general fabrication. It has the best combination of formability, weldability and cost of any common sheet, bends and deep-draws without cracking, and takes any paint, powder coat or plating. Its weakness is corrosion: bare cold-rolled steel will show surface rust within about 48 hours in a damp workshop, so it is always specified with a coating. Typical stock runs from 0.5 to 6 mm, with 0.6 to 3.2 mm the everyday band for enclosures, brackets and chassis.
Galvanised steel is cold-rolled steel with a hot-dip zinc coating already applied, usually quoted as Z275, meaning 275 grams of zinc per square metre, or a corresponding Z100 grade for lighter duty. The zinc protects the steel sacrificially, so a scratch does not immediately become a rust point, which makes SGCC the natural choice for outdoor enclosures, HVAC components and electrical cabinets. Two rules come with it. First, thickness must be measured on the coated sheet, because the coating adds roughly 0.02 mm per side. Second, welding galvanised steel releases zinc fume, so seams need ventilation and usually a touch-up coat over the weld.
Stainless steel: 304 for most things, 316 when chlorides appear
Grade 304 is the general-purpose austenitic stainless, roughly 18 percent chromium and 8 percent nickel, and it needs no coating at all. It is the standard choice for food equipment, medical housings, clean-room panels and architectural trim. Grade 304L is the low-carbon version, chosen whenever a part will be welded heavily because it resists sensitisation and the resulting intergranular corrosion. Both are effectively non-magnetic in the annealed state, which matters for equipment near magnetic fields.
Grade 316 adds 2 to 3 percent molybdenum, which is what gives it resistance to chlorides such as salt water, road spray and many process chemicals. It is the grade for marine hardware, chemical plant, pharmaceutical equipment and surgical instruments, and it typically costs 40 to 60 percent more than 304. That premium is the reason 316 should be specified against a named environment rather than as a habit; using it where 304 would survive spends a large share of the part budget for no benefit. Grade 430 is the ferritic, magnetic, lower-cost stainless used for appliance panels and magnetic shielding, and it is the one grade that must be kept away from magnetic-sensitive equipment.
Aluminium alloys and tempers: the temper matters as much as the alloy
Aluminium is specified as alloy plus temper, and the temper is what decides whether a part can be bent. Grade 5052 in the H32 temper is the default sheet metal aluminium: it has the best formability of the common alloys, tolerates a bend radius of about 0.5 times the thickness, springs back only 2 to 3 degrees and has good corrosion resistance, which is why it covers electronic chassis, lightweight enclosures and transport panels. Grade 6061 in the T6 temper is considerably stronger but much less forgiving; a sharp 90 degree bend will crack it, and the design must keep the inside radius at 2 times the thickness or greater. Grade 7075 is stronger still and must not be bent at all — a forced bend fractures along the line. Grade 3003 is the softer, lower-cost option for lightly formed panels, and 6063 is an extrusion alloy rather than a sheet choice.
Two aluminium-specific points belong on the drawing. Aluminium needs about 30 to 40 percent more laser power than carbon steel for the same thickness because it reflects and conducts heat away quickly, and it should be cut with nitrogen to avoid an oxide edge. And anodising only applies to aluminium, so if the finish is anodising the substrate is already decided; if the finish is powder coating, any of the families will take it.
Copper, brass and bronze: conductivity and spring, with a cost
Copper grade T2, equivalent to C110, is chosen for electrical and thermal conductivity — bus bars, heat spreaders and shielding — and it is soft enough to bend almost without springback. H62 brass, close to C27400, is harder and machines cleanly, so it suits connectors and terminals. Phosphor bronze such as C51000 is the spring material, used for contacts and leaf springs where elasticity matters; because it is rolled to develop that spring, the bend line must run across the grain, not along it, or the part will crack.
The cost of the copper family is real. All three reflect a substantial share of a fibre laser beam, so cutting needs an anti-reflection isolator, runs roughly 30 to 50 percent slower than stainless steel and is usually replaced by stamping or wire EDM in production. Copper and brass are also the most expensive common sheet materials, which is why they normally appear only where conductivity, wear or appearance cannot be met another way.
Choosing a grade in four questions
Four questions resolve most grade decisions, and it is worth answering them on paper before the drawing is frozen. First, what does the part touch: weather, salt, food, chemicals or nothing aggressive at all? That alone separates carbon steel from 316 stainless. Second, how hard is the forming: a flat panel with one bend can use almost anything, while a deep-drawn or multi-bend part wants SPCC or 5052-H32. Third, does weight matter: aluminium is roughly one-third the density of steel, which is decisive on anything carried or moved. Fourth, how will it be joined: carbon and stainless steel weld conventionally, aluminium needs AC TIG, and galvanised steel needs ventilation and a re-coat.
| Decision driver | Best first choice | Why |
|---|---|---|
| Cost, indoor, painted | SPCC carbon steel | Cheapest and most formable |
| Outdoor without coating | SGCC galvanised | Sacrificial zinc protection |
| Food, medical, clean room | 304 or 316L stainless | No coating, cleanable surface |
| Salt or chemical exposure | 316 stainless | Molybdenum resists chlorides |
| Lightweight enclosures | 5052-H32 aluminium | One-third the density, easy to form |
| Structural brackets | 6061-T6 aluminium | Higher strength, wider bend radius |
| Conductivity or spring | T2 copper or C51000 bronze | Electrical, thermal or elastic duty |
Where a grade is the wrong specification
Five situations are worth catching before a quote, because each is a grade that looks reasonable and fails in service. Grade 6061-T6 specified with a sharp bend will crack along the bend line; the grade is fine, the radius is wrong. Grade 7075 specified for a bent part cannot be bent at all. Grade 430 stainless specified near an MRI, a CT scanner or a magnetic sensor will interfere, because it is ferromagnetic. Galvanised steel welded without fume extraction or a post-weld coat turns a corrosion-resistant part into a rust point at the seam. And copper or brass thicker than about 10 mm pushed onto a fibre laser usually moves to waterjet, because the reflectivity risk and the power required rarely justify the cut.
Three further limits belong to the material rather than the drawing. The practical sheet metal range stops around 6 mm; thicker sections need different equipment and often a casting or a machined part. Material cost is not the part cost: a small part cut from a standard sheet nests efficiently, while an awkward contour can waste 30 percent of the sheet however cheap the metal is. And material is only one third of the specification — an identical grade supplied as 2B mill finish, satin brushed or mirror polished behaves the same in the press but looks completely different in service, so the finish has to be named separately.
See sheet metal fabrication for how each grade behaves on the shop floor, custom sheet metal parts for the service built around these materials, and surface finishing for the coating that most carbon steel grades need.
Scope and sources. The six-family material framework, the SPCC, SGCC, SUS304, SUS316, AL5052 and AL6061 grade set with tensile strength, yield strength and density, the SPCC thickness band of 0.6 to 3.2 mm, the SGCC band of 0.8 to 3.2 mm, the SUS304 and SUS316 bands of 0.5 to 6.0 mm, the note that 316 costs about 40 to 60 percent more than 304, the finish options of 2B, brushed and mirror for stainless, and the note that aluminium is about 66 percent lighter than steel at equal thickness come from a precision sheet metal material selection guide. The per-grade processing behaviour — stainless grades 201, 304, 304L, 316L and 430 at 0.5 to 8 mm on a nitrogen cut with 30 to 40 percent slower cutting than carbon steel, 201 springback of 1 to 2 degrees beyond 304, 430 springback of 1 to 2 degrees and a minimum bend radius of 1.5t, 304 springback of 3 to 5 degrees, 304L as the best welding grade, 430 as magnetic and unsuitable for CT and MRI equipment, aluminium 5052-H32 at 0.5 to 6 mm with a bend radius of 0.5t and 2 to 3 degrees of springback, 6061-T6 at 0.5 to 8 mm where a 90 degree sharp bend is prohibited and the radius must be 2t or more, 7075 where bending is strictly prohibited, and the copper grades T2 C110, H62 and C51000 phosphor bronze at 0.1 to 5 mm with the grain direction rule and a laser efficiency 30 to 50 percent below stainless — come from a sheet metal prototyping material reference. The gauge-versus-thickness figures of 16 gauge at 1.52 mm carbon steel, 1.59 mm stainless, 1.29 mm aluminium and 1.61 mm galvanised, the reversed gauge numbering with 26 gauge thinner than 16 gauge, the note that thickness tolerance as tight as 0.003 inch changes bend angles, and the achievable tolerance bands of 0.005 to 0.015 inch on stainless, 0.005 to 0.010 inch on 5052 and 6061 aluminium, 0.010 to 0.020 inch on cold-rolled steel and 0.010 to 0.025 inch on galvanised steel come from a sheet metal gauge chart and from a precision sheet metal guide. The thickness bands of 0.5 to 6 mm for cold-rolled steel and 1.5 to 6 mm for hot-rolled, 0.5 to 4 mm for 304 and 316 stainless, 5052 and 6061 aluminium and 0.5 to 3 mm for copper, brass and galvanised steel, the process tolerances of plus or minus 0.1 mm for laser cutting and punching and plus or minus 0.3 mm for shearing, and the note that cold-rolled steel needs a coating because it rusts untreated come from a sheet metal fabrication guide. These are planning ranges, not quotations.