Aluminum 5052, 6061, 7075: Alloys, Properties & Uses

Aluminum is a light, corrosion-resistant, highly machinable metal that sits behind only steel as the most used structural metal in custom manufacturing. It is roughly one third the density of steel, it forms a passive oxide skin that protects it from corrosion without paint, and it cuts so cleanly that 6061 and 7075 sit at about the machinability rating of free-machining brass. Those three facts explain why aluminum is the default metal for parts that must be strong without being heavy and durable without being painted.

Three wrought alloys cover most of what a designer reaches for. 6061 is the general-purpose alloy, balanced for strength, machinability, and weldability. 5052 is the forming and marine alloy, the most formable of the three, with excellent resistance to saltwater corrosion. 7075 is the high-strength alloy, with a tensile strength of about 83 ksi that approaches steel, used for aerospace and high-stress structural parts. A fourth route, the additive alloy AlSi10Mg, opens geometries that machining and bending cannot reach. This guide compares the three wrought alloys, lays out the properties that drive selection, and walks through the processes, finishes, and design rules that turn a choice of alloy into a finished part.

What aluminum is

Aluminum is a non-ferrous metal, element 13, with a density of about 2.70 grams per cubic centimeter, roughly one third that of steel. It is soft and ductile in its pure form, which is why it is never used pure for structural work; instead it is alloyed with magnesium, silicon, zinc, or copper, which add strength through precipitation hardening. The first digit of the four-digit designation names the family: the 5xxx series (5052) is magnesium-alloyed, known for formability and marine corrosion resistance; the 6xxx series (6061) is magnesium-silicon alloyed, the general-purpose structural and machining alloy; and the 7xxx series (7075) is zinc-copper alloyed, the high-strength aerospace alloy, strongest but lower in corrosion resistance and harder to form.

The temper suffix after the dash sets how the alloy was treated. H tempers, on the 5xxx series, are strain-hardened: H32 is one quarter hard, a soft and formable condition suited to bending. T tempers, on the 6xxx and 7xxx series, are thermally treated: T6 is the peak aged, peak strength condition, T4 is a softer, naturally aged condition better for forming, and T651 is a stress-relieved variant of T6 stretched to remove internal stresses before machining. The same alloy in different tempers behaves very differently, which is why the temper is part of the specification and not an afterthought.

The key alloys: 5052, 6061, and 7075

Aluminum 5052

5052 is the forming and marine alloy. Its tensile strength runs from 31 to 43 ksi (214 to 296 MPa) depending on temper, with the H32 temper the standard for sheet work, and its density is 2.68 grams per cubic centimeter, the lightest of the three. Its defining property is formability: it is the best of the three common alloys for bending, drawing, and spinning, soft enough to form to tight radii without cracking and hard enough to hold a tolerance after forming. It also has the best corrosion resistance of the three, rated very good and suitable for marine service in the H32 temper, which is why it is the alloy for boat hulls, tanks, and parts that face salt spray.

5052 is a sheet and plate alloy, rarely used as bar or extrusion, so it is seldom the choice for a fully machined part, but it is the right choice for any part cut from sheet and then bent or drawn. Its springback is low, around 1 to 3 degrees, and its minimum bend radius in H32 is about 1 to 1.5 times the thickness along the grain, tighter than the other two alloys. H34 and harder tempers may crack at tight radii, so H32 is the forming temper.

Aluminum 6061

6061 is the general-purpose alloy and the most widely used of the three. In the T6 temper its tensile strength is 45 ksi (310 MPa) and its yield strength is 40 ksi (276 MPa), with a density of 2.70 grams per cubic centimeter. Its machinability is rated at about 100 percent of free-machining brass, among the best of the structural aluminum alloys, and it welds very well by MIG or TIG with filler such as ER4043 or ER5356. It is available in every common form, extrusion, plate, bar, tube, and sheet, which is why it is the default for machined brackets, frames, housings, and structural sections.

6061 is good, not excellent, at everything. Its corrosion resistance is good but lower than 5052, and it requires anodizing for marine or chloride service where 5052 would survive bare. Its formability is limited in T6, because T6 springback runs 5 to 10 degrees and the heat-affected zone from welding softens the material and drops the strength. For a part that must be both machined and bent, the stress-relieved T651 temper, or the softer T4, resists cracking better than T6.

Aluminum 7075

7075 is the high-strength alloy. In the T6 temper its tensile strength is 83 ksi (572 MPa), with a yield of 73 ksi and a density of 2.81 grams per cubic centimeter, the heaviest and by far the strongest of the three. Its strength approaches that of steel at one third the density, which is why it is the alloy for aerospace structural parts, high-stress brackets, firearms components, and cycling and sporting goods where strength-to-weight drives selection. Its machinability is also very good, rated at about 100 percent of free-machining brass, so it machines as cleanly as 6061 despite being much stronger.

The cost of that strength is formability and corrosion resistance. 7075-T6 has the lowest elongation of the three, around 10 percent, and it should not be bent: it cracks at the bend line in T6, and forming is limited to the O or W temper, where the strength advantage is lost. Its corrosion resistance is only moderate, and it is susceptible to stress-corrosion cracking, so it needs a protective finish or coating for long-term service. It is not a primary sheet metal alloy; it is used mainly in plate, bar, and extrusion, and it carries a price premium over 6061. In practice 7075 is chosen when 6061 is not strong enough, and avoided otherwise.

Properties at a glance

Lightweight and corrosion resistance

The three alloys share the family traits of aluminum, each in a different balance. Lightweight is common to all: at about 2.7 grams per cubic centimeter, aluminum is roughly one third the density of steel, and the strength-to-weight ratio drives its use in transport and aerospace, where 7075 reaches a strength-to-weight that competes with steel at a fraction of the mass. Corrosion resistance comes from a passive oxide layer that forms on exposure to air: strongest in 5052 (the marine alloy), good in 6061 but needing anodizing for chloride service, and only moderate in 7075, which needs protection for long-term outdoor use.

Machinability and formability

Machinability is where 6061 and 7075 stand out, both rated at about 100 percent of the free-machining brass standard, which means fast cycle times and fine surface finishes. The caveat is that aluminum is soft and ductile, so it tends to weld to a sharp cutting edge and build up on the tool, a tendency called built-up edge, managed with carbide tooling, sharp polished edges, and flood coolant. Formability is where the alloys differ most: 5052 bends and draws to tight radii with elongation of 12 to 20 percent and the lowest springback; 6061 in T6 is formable only for simple bends at generous radii; and 7075 in T6 is effectively not bent. The choice of alloy for a formed part is therefore dominated by the forming requirement, not by the strength requirement.

Processes

CNC machining

CNC machining is the natural home of 6061 and 7075. Both are available in bar, plate, and extrusion, both hold tight tolerances, with 6061-T6 capable of about plus or minus 0.001 inch (0.025mm) on suitable work, and both machine at the rating of free-machining brass. Machined aluminum is the default for brackets, housings, fittings, manifold blocks, and any part needing precision features, threaded holes, or flat mating surfaces, and the sticky-chip tendency is managed with carbide tooling and flood coolant.

Sheet metal bending

Sheet metal bending is the natural home of 5052. Cut from sheet on a laser or punch, then bent on a press brake, 5052-H32 forms to tight inside radii with low springback and no cracking, which makes it the alloy for enclosures, panels, brackets, and tanks. 6061 can be bent in softer tempers at larger radii, but it is not the bending alloy; 7075 should not be bent in T6 at all. The bend rules apply per alloy: minimum inside radius of at least half the thickness as a general floor, with 5052 holding tighter radii and 6061 needing two to six times the thickness in T6 along the grain.

Additive manufacturing (AlSi10Mg)

Additive manufacturing opens a different route, in the alloy AlSi10Mg. Printed by laser powder bed fusion (DMLS or SLM), it builds parts layer by layer from powder, which allows internal channels, lattice structures, and consolidated geometries that machining and bending cannot produce. It is a casting-type alloy, silicon and magnesium rich, with decent strength but not a direct substitute for 6061 or 7075 in wrought properties. The as-built surface is rough, around Ra 5 to 10 micrometers, and tolerances run about plus or minus 0.3 percent with a 0.3mm floor, so critical faces are usually machined after printing. Additive aluminum suits low-volume complex parts, such as heat exchangers with internal cooling channels.

Anodizing and finishing

Aluminum takes a wider range of finishes than almost any other structural metal, and the finish is often part of the specification. Anodizing is the signature finish: it converts the surface oxide into a thicker, harder, controlled layer, which hardens the surface, improves corrosion resistance, and accepts a dye for color. Type II, sulfuric anodizing, is the standard cosmetic and protective finish, and it adds about 10 to 15 micrometers to the surface, half grown into the metal and half built up above it, a dimensional change that has to be planned on close-fitting features. Type III, hardcoat anodizing, builds a thicker, harder layer suited to wear surfaces. Anodizing is essential for 6061 in marine or outdoor service, and it is the default finish for cosmetic housings and consumer parts. For example, an anodized 6061 enclosure holds its color and resists corrosion where a bare 6061 part would pit. The process removes a small amount of metal, so threads and tight clearances are specified with the finish in mind.

Other finishes extend the range. Powder coating and wet paint apply over a chromate or conversion coat, for parts that need a specific color or a thicker coating than anodizing provides. Bead blasting produces a uniform matte surface that hides machine marks, and brushing and polishing give a cosmetic surface for decorative and architectural parts. For parts that need no finish at all, the bare as-machined or as-formed surface is acceptable for many internal and non-cosmetic applications, since the passive oxide already protects it.

A choose-alloy decision guide

The choice falls out of three questions: does the part bend, how strong must it be, and what environment does it serve?

If the part is formed or bent from sheet, choose 5052-H32, the formable alloy with the lowest springback and the best resistance to cracking at the bend line, and the only one of the three suited to tight radii. If the part is cut from sheet but not bent, 6061-T6 is a stronger alternative. Do not specify 7075 for a bent part.

If the part is machined, choose 6061-T6 as the default: strong enough for most structural work, top of the machinability range, weldable, and available in every form. Move up to 7075-T6 only when 6061 is not strong enough for the load, accepting the price premium and the need for a protective finish. e.g., a high-stress aerospace bracket that must minimize weight at a given strength pushes the choice to 7075, while a general structural bracket stays in 6061.

If the part serves a marine or chloride environment, choose 5052-H32 for formed parts or 6061 with anodizing for machined parts. 5052 resists saltwater corrosion bare. 6061 needs anodizing for the same service, and 7075 needs a protective coating and should be avoided in marine exposure, where its stress-corrosion cracking susceptibility is a risk.

Applications

Aerospace

Aerospace is the home of 7075. Its strength-to-weight ratio, with a tensile of 83 ksi at one third the density of steel, makes it the alloy for aircraft structural parts, wing and fuselage fittings, high-stress brackets, and sporting goods such as bicycle frames and firearm receivers where every gram matters and the load is high. 6061 also serves in aerospace for secondary structure and for parts where its better corrosion resistance and weldability matter more than peak strength.

Marine

Marine is the home of 5052. Its resistance to saltwater corrosion, combined with its formability, makes it the alloy for boat hulls, deck fittings, fuel and water tanks, marine hardware, and any part that faces salt spray. 6061 with anodizing serves where a machined marine part is needed, since 5052 is rarely used as bar stock. 7075 is not a marine alloy.

Automotive and general fabrication

Automotive splits across all three: 6061 for machined and structural parts, frames, and extruded sections; 5052 for body panels and formed parts that need bendability; and 7075 for high-stress, weight-critical components such as suspension and drivetrain parts in performance and racing. For general fabrication, enclosures, brackets, jigs, and fixtures, 6061 is the default, chosen for its balance of strength, machinability, availability, and cost. HVAC ductwork, heat exchangers, signage, and consumer electronics housings all draw on the same set of alloys, with 5052 for formed work and 6061 for machined and structural work.

Alternatives and when not to use aluminum

Aluminum is the right choice when lightness, corrosion resistance, and machinability matter together, but it is not the right choice everywhere. Where raw strength or wear resistance dominates, steel is stronger and harder: carbon steel reaches tensile strengths of 58 to 100 ksi and stainless reaches 73 to 87 ksi, both at higher hardness and better wear resistance, so any part that sees heavy wear or needs a hardened surface is better in steel. The trade-off is weight and corrosion resistance, since steel is three times the density and rusts or stains unless protected.

Where higher strength-to-weight is needed, titanium competes with 7075. Ti-6Al-4V reaches tensile strengths of 130 to 160 ksi at a density of 4.43 grams per cubic centimeter, about 60 percent of steel, which gives it a strength-to-weight that can exceed 7075. The trade-off is cost and machinability: titanium is expensive and difficult to machine, with low thermal conductivity that drives heat into the tool, so it is reserved for aerospace, medical, and high-end sporting parts. Where weight or cost dominates and the loads are modest, engineering plastics such as glass-filled nylon, PEEK, and acetal step in, at the cost of an order of magnitude less stiffness and far lower service temperatures.

Do not use aluminum when the part sees sliding wear without lubrication, because aluminum galls and seizes on steel and even on itself, and a wear surface needs a hardcoat, an insert, or a different material. Do not use it when the service temperature exceeds about 200 degrees Celsius, because aluminum loses strength rapidly with temperature. And do not use 7075 where corrosion resistance matters without a plan for protection, because its stress-corrosion cracking susceptibility makes bare 7075 a poor choice for long-term outdoor or marine service.

Tolerances and design notes

Aluminum 6061-T6 machines to about plus or minus 0.001 inch (0.025mm) on suitable CNC work, which places it among the most accurately machinable of the structural metals. Standard commercial CNC tolerance runs about plus or minus 0.005 inch (0.13mm), and precision work reaches plus or minus 0.002 inch (0.05mm), with the tightest tolerances reserved for ground or precision-machined features. 7075 machines to similar tolerances; 5052 is rarely machined to tight precision because it is used mainly as formed sheet. The as-machined surface finish runs about Ra 3.2 micrometers (125 microinches), and finer finishes are reached with a finish pass or with grinding.

For sheet metal work, the tolerances follow the bending rules. Bend angle tolerance on aluminum runs about plus or minus 1 degree standard, with plus or minus 0.5 degree achievable on soft tempers with good tooling, and linear dimensions hold about plus or minus 0.25mm. Springback is the variable that drives accuracy: 5052-H32 springback is about 1 to 3 degrees, predictable and easy to compensate; 6061-T6 springback is 5 to 10 degrees and must be overbent to hit angle; 7075-T6 should not be bent. Minimum inside radius follows the alloy, with 5052 holding about 1 to 1.5 times the thickness in H32 and 6061-T6 needing 2 to 6 times the thickness depending on direction and gauge.

A few design notes apply across the alloys. Specify the temper with the alloy, because 6061-T6 and 6061-T4 are different materials for forming. Allow for the anodizing dimensional change, about 10 to 15 micrometers, on close-fitting and threaded features. Use carbide tooling, sharp edges, and flood coolant to manage the sticky-chip tendency, and design generous radii into internal corners to avoid stress concentrations that can initiate cracks, especially in the higher-strength 7075. For bent parts, orient bends across the rolling grain where possible, because bending across grain allows tighter radii than bending along it. And for any part that serves outdoors or in marine service, match the alloy to the environment, 5052 bare, 6061 anodized, 7075 protected, so the corrosion resistance holds for the life of the part.