Aluminum 5051: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

5051 is a member of the 5xxx series of aluminum alloys, which are magnesium-strengthened, non-heat-treatable alloys. Its primary alloying element is magnesium, typically in the low-to-mid percentage range, with trace levels of manganese and chromium to refine grain structure and improve corrosion resistance. Strengthening is achieved almost exclusively through solid-solution strengthening and strain hardening rather than precipitation heat treatment, which places 5051 in the same processing class as other 5xxx alloys.

Key traits of 5051 include a favorable balance of moderate strength, good corrosion resistance (especially in marine and chloride environments), and excellent weldability. Formability in softer tempers is good to excellent, and the alloy responds predictably to cold working for incremental strength increases. Typical industries that leverage 5051 include marine construction, transportation (trailer and van bodies), pressure vessels, and some architectural applications where corrosion resistance and moderate strength are prioritized.

Engineers choose 5051 over other alloys when they need improved strength compared with commercially pure aluminum while retaining better marine corrosion resistance compared with many work-hardened 3xxx alloys. It is selected where welding and post-weld performance are important and where heat-treatment is impractical or unnecessary. Cost and availability are additional drivers; 5051 often offers an attractive cost-performance position for structural panels, extrusions, and welded assemblies.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (20–35%)	Excellent	Excellent	Fully annealed, maximum ductility and formability
H12	Moderate	Moderate (12–20%)	Good	Excellent	Partial hardening, limited forming after tempering
H14	Moderate-High	Moderate (8–15%)	Good	Excellent	Quarter-hard, common for sheet forming and moderate strength
H18	High	Low (6–12%)	Limited	Excellent	Full hard, used where higher yield is required without anneal
H22	Moderate (stabilized)	Moderate	Good	Excellent	Strain-relieved after partial hardening for stability in fabrication
H32	Moderate-High	Moderate	Good	Excellent	Strain-hardened and stabilized, common for welded structures
H111	Moderate	Moderate	Good	Excellent	Temporary strain-hardened condition for limited forming operations

Temper selection for 5051 controls the trade-offs between strength and ductility; colder tempers give higher yield and tensile strength at the cost of reduced elongation and forming ability. Because 5051 is non-heat-treatable, the H-series family (cold work and strain relief) is the mechanism by which manufacturers and fabricators tune mechanical performance for specific parts and production methods.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.25	Controlled low silicon to avoid brittleness and maintain weldability
Fe	≤ 0.40	Typical impurity element; excessive Fe can reduce formability
Mn	≤ 0.20	Small additions improve strength and resistance to grain-boundary corrosion
Mg	2.2–2.8	Primary strengthening element; governs corrosion performance and work-hardening response
Cu	≤ 0.10	Kept low to preserve corrosion resistance and weldability
Zn	≤ 0.25	Minor; higher Zn increases strength but may promote galvanic issues
Cr	0.05–0.25	Microalloying to control grain structure and improve strain-aging resistance
Ti	≤ 0.15	Grain refiner used in some cast or wrought products
Others	≤ 0.15 total	Includes V, Zr, etc., kept low to maintain consistent properties

The alloy chemistry centers on magnesium for solid-solution strengthening while keeping copper and zinc low to preserve corrosion resistance and welding behavior. Minor levels of chromium and manganese help control recrystallization and grain growth during processing, which improves toughness and resistance to intergranular corrosion in fabricated parts.

Mechanical Properties

Tensile behavior of 5051 is typical for a medium-strength 5xxx alloy: the annealed (O) condition exhibits modest tensile and yield strength with relatively high elongation, while H-temper conditions produced by cold work increase yield and tensile strength substantially at the cost of ductility. Yield behavior is progressive with increasing cold work and temper designation; H12/H14 produce measurable gains in yield while H18 or H32 provide the highest wrought strengths reachable without heat treatment. Hardness follows yield trends and is commonly measured to monitor process control in stamping and forming operations.

Fatigue performance is sensitive to surface condition, processing, and working environment; polished and well-welded 5051 exhibits reasonable high-cycle fatigue life for structural applications, but fatigue cracks initiate preferentially at welded joints and stress concentrators. Thickness effects are significant: thinner gauges are easier to cold-work to higher strength levels, while plate and thick extrusions retain more residual ductility in softer tempers and can be challenging to achieve uniform through-thickness strength without upsetting operations.

Property	O/Annealed	Key Temper (e.g., H14/H32)	Notes
Tensile Strength	110–145 MPa	210–275 MPa	Values depend on thickness and degree of cold work
Yield Strength	40–75 MPa	150–240 MPa	H-temper increases yield substantially through strain hardening
Elongation	20–35%	6–15%	Ductility decreases with increasing temper/hardness
Hardness	25–35 HB	55–85 HB	Hardness correlates with cold-work and is used for QC on fabricated parts

Physical Properties

Property	Value	Notes
Density	2.68 g/cm³	Typical for wrought aluminum alloys; favorable strength-to-weight ratio
Melting Range	~605–655 °C	Alloying broadens melting range slightly below pure Al melting point (660 °C)
Thermal Conductivity	~130 W/m·K	Good thermal conductivity, slightly lower than pure aluminum
Electrical Conductivity	~34–44 % IACS	Reduced relative to pure Al due to Mg in solid solution
Specific Heat	~900 J/kg·K	Typical specific heat for aluminum alloys at ambient temperatures
Thermal Expansion	23.0–24.5 µm/m·K	Moderate coefficient; important for multi-material assemblies

5051 retains many of aluminum’s attractive physical properties: light weight and high thermal conductivity relative to steels, making it useful for thermal management and lightweight structures. The combination of density and mechanical properties yields good specific strength, but designers must account for thermal expansion when mating 5051 to dissimilar metals or when used in temperature-cycling environments.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.4–6 mm	Readily cold-worked; thin gauges achieve higher H-temper strengths	O, H14, H18, H32	Widely used for panels, cladding, and enclosures
Plate	6–50 mm	Reduced cold-workability; often supplied in softer tempers for machining	O, H112, H32	Structural plates and thicker fabricated components
Extrusion	Complex profiles	Strength depends on post-extrusion cold work; can be age-stabilized	O, H32	Common for frames, rails, and marine sections
Tube	1–12 mm wall	Similar to sheet; welded or seamless options affect properties	H14, H32	Used in structural tubing and piping for corrosion exposure
Bar/Rod	Ø3–100 mm	Cold-drawn bar increases strength; machining stock often softer	O, H18, H22	Fittings, pins, and turned components

Processing route (rolling, extrusion, drawing) affects recrystallization and anisotropy in mechanical properties; sheet and thin gauges are the most economical forms and are the easiest to cold-work into higher-strength H-tempers. Extrusions and plates are chosen when cross-sectional features or thicker sections are required, but they may require additional stress-relief or controlled cooling to avoid distortion in welded assemblies.

Equivalent Grades

Standard	Grade	Region	Notes
AA	5051	USA	Aluminum Association designation for wrought 5xxx-series Mg alloy
EN AW	5051	Europe	EN AW-5051 commonly used; chemical and mechanical limits similar to AA
JIS	A5051	Japan	JIS variants align compositionally but may specify different mechanical test conditions
GB/T	5051	China	Chinese standard grade with comparable composition; processing tolerances may differ

Differences between standards are typically in specified tolerance bands, required mechanical testing methods, and permitted impurity limits rather than fundamental chemistry. Engineers should verify mill certificates for critical applications to ensure compliance with local standards for properties, tempers, and processing routes.

Corrosion Resistance

5051 exhibits very good atmospheric corrosion resistance that is characteristic of the 5xxx series due to its magnesium content and low copper levels. The alloy forms a protective oxide film that provides pitting resistance in many outdoor and mildly aggressive environments. In marine exposure and chloride-rich atmospheres, 5051 performs well relative to many 3xxx and 6xxx alloys, although long-term immersion and stagnant saltwater can still produce localized attack if surface coatings fail.

Stress corrosion cracking (SCC) sensitivity in 5051 is lower than higher-Mg 5xxx alloys (those with >3.5% Mg), but SCC cannot be entirely discounted for highly stressed members in aggressive environments. Residual tensile stresses from forming or welding increase SCC risk, so proper design detail, post-weld stress relief, and material selection are important in critical structural components. Galvanic interactions must be managed when 5051 is coupled to more noble metals such as stainless steel or copper; appropriate isolation or sacrificial anodes are common mitigation measures in marine and architectural assemblies.

Compared with other alloy families, 5051 offers superior marine corrosion resistance versus many heat-treatable alloys (e.g., 6xxx series) that contain copper or higher zinc levels, while yielding somewhat lower peak strength than 6xxx alloys that have been age-hardened. Designers often select 5051 when durability in chloride environments and weldability are prioritized over maximum achievable strength.

Fabrication Properties

Weldability

5051 is readily welded with common fusion processes including TIG (GTAW) and MIG (GMAW). Welds in 5051 typically display good puddle fluidity and low hot-cracking susceptibility because the composition is free of significant copper and contains modest magnesium. Recommended filler metals are commonly 5356 (Al-Mg) for higher strength and good corrosion resistance, or 4043 (Al-Si) for improved weldability in some situations; choice depends on desired post-weld strength and anodizing behavior. Designers should be mindful of HAZ softening if base metal is in a strain-hardened temper and follow appropriate post-weld stabilization or local heat treatment practices when necessary.

Machinability

Machinability of 5051 is moderate; it machines more readily than higher-strength alloys but less readily than commercially pure aluminum. Tools with carbide tips and positive rake geometry are recommended to manage chip formation and avoid built-up edge; coolants or lubricants improve surface finish and tool life. Cutting speeds are moderate, and feeds should be optimized to prevent work hardening at the cut surface which can affect finishing passes. For high-volume turning or milling, tool coatings and rigid fixturing reduce chatter and extend tool life.

Formability

Formability is excellent in the annealed (O) condition and remains very good in light H-tempers such as H12 and H14, making 5051 suitable for deep drawing, bending, and stretch forming. Minimum bend radii should reference temper and thickness, but general practice for sheet forming is a bend radius of 1–3× the material thickness in softer tempers; tighter radii require annealing prior to forming or use of softer tempers. Cold-work significantly increases strength and reduces ductility, so progressive forming operations should be sequenced to avoid cracking and may require intermediate anneals for complex geometries.

Heat Treatment Behavior

5051 is a non-heat-treatable alloy and therefore does not respond to solution treatment and artificial aging to develop strength; its mechanical property changes are achieved by controlled cold working and temper designations. Standard thermal cycles used for heat-treatable alloys (solutionizing and quenching followed by aging) are not effective for producing a precipitate-hardened condition in 5051, so designers should not rely on T-temper gains for this grade.

Annealing is used to restore ductility after heavy cold work; full anneal for 5051 is typically performed in the range of approximately 350–415 °C with controlled cooling to achieve the O temper. Stabilization treatments (e.g., H22 or H32) involve low-temperature heat or stress-relief steps to minimize strain aging and to provide predictable dimensional stability for fabrication and welding. Work-hardening schedules and temper controls are part of the mill processing route to deliver material with target yield and tensile ranges for forming or structural use.

High-Temperature Performance

At elevated temperatures, 5051 loses strength progressively as solid-solution strengthening becomes less effective and recovery processes accelerate; practical continuous-use temperatures for structural integrity are generally limited to below about 100 °C for applications requiring rated strength. Creep resistance at moderately elevated temperatures is limited compared with specialty high-temperature alloys, and sustained loads at elevated temperatures will cause measurable deformation over time. Oxidation in air is minimal because aluminum forms a stable oxide, but high-temperature exposure can alter surface appearance and affect subsequent surface treatments or coatings.

Welded joints can show localized softening in the heat-affected zone (HAZ) due to thermal exposure; designers must consider this for elevated service temperatures because the HAZ may become the limiting region for strength retention. For applications requiring higher temperature capability, alternative alloys or design allowances should be considered.

Applications

Industry	Example Component	Why 5051 Is Used
Automotive	Body panels, fuel tanks	Good formability, weldability, and corrosion resistance
Marine	Hull panels, deck structures	Superior chloride pitting resistance and weldability
Aerospace	Fittings, fairings (non-critical)	Favorable strength-to-weight and corrosion performance
Electrical/Heat Management	Heat sinks, housings	Good thermal conductivity and manufacturability
Architecture	Cladding, facades	Weather resistance and aesthetic anodizing capability

5051 is widely used where the combination of corrosion resistance, weldability, and reasonable strength is required without the overhead of heat treatment. Its balance of properties supports diverse applications from marine structures to lightweight fabricated assemblies where service environment and fabrication method drive alloy choice.

Selection Insights

Choose 5051 when you need a non-heat-treatable alloy with better strength than commercially pure aluminum and superior corrosion resistance in chloride-laden environments. It is particularly attractive when welding and forming are required and when designers prefer predictable behavior from strain-hardening rather than age-hardening processes.

Compared with 1100 (commercially pure Al), 5051 trades some electrical conductivity and ultimate formability for substantially higher strength and improved marine performance. Compared with 3xxx series alloys (for example 3003 or with 5052), 5051 provides comparable or slightly higher strength with similar corrosion resistance, making it a middle ground for strength vs. ductility. Compared with heat-treatable alloys such as 6061/6063, 5051 offers easier welding and better chloride corrosion resistance even though it cannot reach the peak strength of age-hardened 6xxx alloys; use 5051 when in-service corrosion resistance and weld integrity outweigh maximum achievable strength.

• Prefer 5051 for welded marine structures and corrosion-exposed fabricated parts.
• Prefer 6061 if peak structural strength and machinability are critical and corrosion is controlled.
• Prefer 1100/3003 for optimal formability or electrical conductivity where high strength is not required.

Closing Summary

5051 remains a practical, well-rounded aluminum alloy for applications that require a robust balance of corrosion resistance, weldability, and moderate strength without reliance on heat treatments. Its predictable behavior under cold work and broad availability in common product forms make it a cost-effective choice for marine, transportation, and structural fabrication tasks where long-term durability in aggressive environments is required.