Should I use cold rolled steel or galvanized sheet?

Cold rolled steel for interior parts where you will powder coat or paint anyway; galvanized sheet for parts exposed to moisture, or where you want a consistent appearance without painting. Galvanized costs more per kilogram and has slightly worse formability and weldability, and the zinc burns off at the laser cut edge, leaving bare steel that will rust unless protected. Many buyers get this wrong and then reject parts for edge rust.

When should I choose stainless over carbon steel?

Stainless when the part sees moisture, chemicals, food contact or elevated temperature, or when appearance must not oxidise. 304 is the general-purpose grade; 316L adds molybdenum for chloride resistance and is the right choice near salt or marine exposure. Carbon steel is the default for everything else: cheaper, easier to cut and bend, and it holds a tighter cosmetic finish once coated.

Is aluminium always the better choice for a lightweight part?

No. Aluminium is roughly one third the density of steel, so the same part weighs about 65 percent less, but it costs more per kilogram, is more expensive to cut on a per-part basis, and springs back more when bent. If stiffness matters rather than mass, aluminium is the weaker choice: its modulus is about one third of steel's, so a panel needs to be thicker or more braced to be equally stiff.

What is the difference between CR, HR and galvanized sheet?

Cold rolled steel is processed at low temperature: smoother, more accurate thickness, better surface for painting. Hot rolled is cheaper and rougher, normally used for thicker structural sections. Galvanized is cold rolled or hot rolled with a zinc coating for corrosion protection. For laser-cut-and-bend work above about 3mm, hot rolled becomes common because it is cheaper and the surface finish matters less.

Which aluminium grade should I specify?

5052 for general sheet metal and marine exposure - it has the best corrosion resistance and formability of the common alloys. 6061 is the strongest readily available grade with good weldability, a good general choice for machined parts. 6061-T6 is stiffer but springs back more. 5052-H32 is the usual form for bent sheet; 6061-T6 is the usual form for machined components.

Does material choice change my tolerance stack?

Yes, mainly through bend angle. Aluminium and stainless spring back significantly more than mild steel, so the same press brake and the same drawing produce a wider spread of final angles. Hole position after bending also shifts, because the neutral axis moves with the K-factor of the material. See the tolerance and surface finish page for the numbers.

What about galvanized coating thickness?

Specify the coating mass, commonly expressed as g/m2 per side: Z100, Z180, Z275. Heavier coatings protect longer outdoors but add cost and reduce formability slightly. If the part will be powder coated afterwards, tell the supplier - the coating affects weld appearance and surface prep, and a heavy coating can flake near welds.

How do I decide between two materials for a real product?

Rank the requirements in this order: environment and corrosion exposure, then required stiffness or weight, then cosmetic finish, then cost. Material choice is dominated by environment and mechanics; cost is usually the last differentiator, and switching from carbon steel to stainless to solve a corrosion problem is often cheaper than specifying a coating system that fails in service.

Sheet Metal Material Selection

Most sheet metal material decisions look like cost engineering and are actually corrosion engineering. This page compares the four material families you will realistically choose between — carbon steel, galvanized sheet, stainless and aluminium — on how they cut, how they form, how they weld, how they age, and what each one costs.

The Four Material Families Compared

Property	Carbon Steel	Galvanized Sheet	Stainless	Aluminium
Density	7.85 g/cm³	7.85 g/cm³	7.90 g/cm³	2.70 g/cm³
Relative cost	Lowest	Low	High (2–4×)	Medium-high
Laser cut speed	Fastest	Fast	Medium (needs clean cut)	Medium
Bend / spring-back	Low, forgiving	Low	High	High
Weldability	Easy (MIG/TIG)	Fair — zinc fumes	Good, TIG preferred	Good, needs clean oxide
Corrosion resistance	Poor bare	Good, edge exposed	Excellent	Good (5052 best)
Stiffness (modulus)	200 GPa	200 GPa	193 GPa	70 GPa — one third
Best for	Indoor painted parts	Outdoor, damp exposure	Food, chemical, clean	Weight-critical, coastal

Carbon Steel: The Default

If nothing in the requirements forces a different choice, carbon steel is the answer. It cuts fastest, bends most repeatably, welds easily, and takes paint or powder coat well. Its weakness is that bare carbon steel rusts — which is a specification problem, not a material problem.

Form	Typical Grades	Use When	Notes
Cold rolled (CR)	Q235 / S235JR, DC01	Thickness below roughly 3mm, painted or coated parts	Smooth surface, accurate thickness, best for bending and paint adhesion.
Hot rolled (HR)	Q235B, S355JR	Structural parts, 3mm and above, rarely painted to a fine finish	Cheaper and rougher. Surface scale must be removed before coating or welding.
Galvanized	SGCC, DX51D, Z100/Z180/Z275	Outdoor or damp environments, or uncoated appearance	Zinc burns off at the laser cut edge. Specify edge protection.
Pre-plated / pre-painted	RAL or Pantone coated	Visible parts where no secondary coating is wanted	Cannot be welded without destroying the coating near the weld. Tends to be scratched in handling.

Stainless: When Corrosion Decides

Stainless earns its cost when the environment is wet, salty, chemically aggressive or food-contact. It does not need a coating to survive, and it keeps its appearance for years without maintenance.

Grade	Key Characteristic	Use When
304 / 304L	General purpose austenitic	Dry indoor environments, general fabrication, food equipment
316 / 316L	Molybdenum added, chloride resistant	Marine, salt spray, chemicals, outdoor coastal exposure
430	Ferritic, lower cost, magnetic	Interior panels and appliances where full corrosion resistance is not needed
303	Free-machining, sulfur added	Machined stainless components, not for welding

Two stainless-specific traps. First, spring-back is much higher than on mild steel, so expect 4–7° at 90° and budget over-bend. Second, welding stainless without proper gas purging leaves a discoloured, oxidised seam that will rust; TIG with purge is the standard. See welding distortion control.

Aluminium: Light, but Not Always Better

Aluminium cuts the weight of a part roughly by two thirds, which is decisive in transport, handheld equipment and aerospace-adjacent builds. It is also one third as stiff as steel, so the same stiffness requires greater thickness or more bracing — and that is where the weight advantage starts to disappear.

Grade	Form	Character	Use When
5052	H32 sheet	Best corrosion resistance and formability of the common alloys	Marine, general sheet metal bending
6061	T6	Strong, good weldability, the general engineering alloy	Mixed parts, machined components, structural
6063	T5/T6	Easier to extrude and finish, lower strength	Extruded profiles, decorative parts
7075	T6	Highest strength common alloy, poor weldability	Highly loaded machined parts, not welded assemblies

Watch the surface. Aluminium reflects most of the laser beam back at the source, and an oily or marked sheet produces spatter instead of a clean cut. It also forms a hard oxide layer that must be removed before welding or bonding. Say so on the drawing if the part is cosmetic.

Decision Guide by Application

Application	Recommended Material	Reason
Electronics enclosure, indoor	Cold rolled steel, powder coated	Cheapest, stiffest, best cosmetic finish after coating
Cabinet or enclosure outdoors	Galvanized steel, powder coated	Zinc for base protection, coating for appearance
Marine or coastal	316L stainless or 5052 aluminium	Both resist chloride; choose on appearance and cost
Food or medical contact	304 or 316L stainless	Non-reactive, cleanable, no coating to fail
Weight-critical cover	5052-H32 aluminium	Mass reduction without a strength requirement
Structural bracket, painted	Q235 or S355 cold rolled	Strength and stiffness at the lowest cost
Heat-exposed component	Stainless or aluminium over carbon steel	Carbon steel loses temper and distorts near heat sources
Cold or cryogenic service	316L stainless	Ductility retained at low temperature; aluminium becomes brittle

Material and Finish Interact

The material choice constrains the finishing options, and getting the pair wrong is a frequent cause of rejected first articles.

Galvanized + powder coat: works, but surface prep is critical and welding near a coated surface damages the zinc.
Stainless + powder coat: rarely specified. If you want colour on stainless, discuss it early — it is unusual and adds cost.
Aluminium + anodizing: the natural pairing. Anodizing is a dielectric layer, so it adds a small dimensional increase on the order of half the coating thickness per side.
Pre-painted sheet + welding: the coating burns back. Specify whether the weld is cosmetic, structural or both before quoting.
Passivation: specified for stainless in food, medical or chemical service. It removes free iron contamination and is cheap insurance against later rust spots.

Common Mistakes

#	Mistake	Consequence	Correct Approach
1	Galvanized sheet with no edge protection specified	Cut edge rusts within weeks and parts are rejected	Specify powder coat or edge sealing, or accept bare edges for indoor use only.
2	316L specified where 304 would do, or vice versa	Over-specification cost, or premature corrosion	Match the grade to the actual chloride and chemical exposure.
3	Aluminium chosen for weight without checking stiffness	Part is thinner, weaker and still heavier once braced	Compare on stiffness-to-weight, not density alone.
4	7075 specified on a welded assembly	Poor weldability, heat-affected cracking	Use 6061 or 5052 for welded parts; 7075 for machined only.
5	Spring-back not considered for stainless or aluminium bends	Flange does not match its mating part	Allow for material spring-back; verify on the first article.
6	Hot rolled specified where a painted finish is expected	Mill scale shows through coating, poor adhesion	Cold rolled for painted parts; hot rolled only for structural work.
7	Material grade omitted from the drawing	Supplier substitutes a similar grade, properties differ	State the grade and the temper or coating condition.
8	Anodizing specified without acknowledging dimensional growth	Sliding fits no longer fit after finishing	Account for coating buildup in fit dimensions, or finish then machine.

Related Sheet Metal Pages

Design for Sheet Metal — minimum flange, radius and hole spacing rules
Bend Radius and Bend Allowance — K-factor and spring-back by material
Tolerance and Surface Finish — how material and coating move your dimensions
Sheet Metal Fabrication Service — thickness limits by material

Not sure which grade to write on the drawing? Tell us the environment and the load and we will propose a grade with the reasoning — including when the cheapest option is actually adequate.

Ask About Your Application

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