Aluminum 5059: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

5059 is a member of the 5xxx series of aluminum alloys, placing it squarely in the Al–Mg family. It is primarily alloyed with magnesium and minor amounts of manganese and chromium to raise strength and enhance corrosion resistance relative to lower-magnesium 5xxx alloys.

The principal strengthening mechanism for 5059 is solid-solution strengthening supplemented by microalloying and controlled thermomechanical processing; it is not a conventional heat-treatable alloy. Strength is developed via cold work and by controlling precipitate and dispersoid chemistry during processing, giving a good combination of high strength and retained toughness.

Key traits of 5059 include high tensile and yield strength for a non-heat-treatable aluminum, superior marine corrosion resistance, good weldability with appropriate filler metals, and reasonable formability in annealed tempers. Typical industries that exploit 5059 are marine and shipbuilding, offshore structures, transport (rail and specialty automotive), and airframe fittings where corrosion resistance and weight savings are critical.

Engineers select 5059 when they need a non-heat-treatable alloy that approaches the strength of lower-end heat-treatable alloys while maintaining superior resistance to seawater and stress-corrosion cracking. The alloy is often chosen over 5000-series peers for higher strength, and over 6xxx/7xxx alloys where corrosion performance and weldability are prioritized.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, best ductility and forming capability
H111	Low-Medium	High	Very Good	Very Good	Slight work-hardening from a single strain, good for modest forming
H116	Medium-High	Moderate	Good	Good	Stabilized strain-hardened temper widely used in marine environments
H321	Medium-High	Moderate	Good	Good	Strain-hardened and thermally stabilized by minor heat treatment
H34 / H36	High	Low-Moderate	Limited	Good	Heavier strain hardening for maximum strength in non-heat-treatable state
T (limited applicability)	Variable	Variable	Variable	Variable	Some commercial T-tempers may exist after limited solution + aging; not primary strengthening route

Temper critically governs 5059’s balance of strength, ductility, and fabricability. Annealed (O) material allows deep drawing, complex stamping and bending, while H1x/H11x styles offer incremental increases in strength with moderate loss in elongation, suiting formed but not heavily bent parts.

Higher strain-hardened tempers (H3x/H34/H36) maximize yield and tensile strength for structural members but substantially reduce bendability and stretch formability; welding typically reverts the HAZ to softer conditions and must be considered in joint design.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.40	Controlled low silicon to limit brittle intermetallics and maintain toughness
Fe	≤ 0.50	Typical impurity level; excessive Fe forms brittle phases that reduce ductility
Mn	0.2–1.0	Improves strength and grain structure; helps control recrystallization
Mg	4.5–6.0	Principal strengthening element, improves corrosion resistance in marine atmospheres
Cu	≤ 0.10	Kept low to avoid reduced corrosion resistance and SCC susceptibility
Zn	≤ 0.25	Low zinc to avoid hot-cracking and preserve corrosion performance
Cr	0.20–0.50	Microalloying element that refines grain structure and stabilizes mechanical properties
Ti	≤ 0.10	Grain refiner when added in small amounts during casting/extrusion practice
Others (each)	≤ 0.05	Minor elements and residuals; total others typically limited

The alloy chemistry is tuned to maximize Mg-driven solid-solution strengthening while keeping copper and zinc low to preserve corrosion resistance. Chromium and manganese are intentionally added to refine grain structure, inhibit recrystallization during thermomechanical processing, and stabilize strength after welding or thermal exposure.

Mechanical Properties

In service, 5059 displays a tensile/yield profile strongly dependent on temper and thickness. Annealed material yields modest strength (comparable to many 5xxx alloys) with high elongation, whereas strain-hardened and stabilized tempers deliver high yield levels approaching lower-tier heat-treatable alloys. Fatigue performance is generally good for a marine-grade alloy provided surface condition and weld details are managed to minimize notches.

Yield strength in high-strength tempers is high while retained ductility is moderate; engineers must account for reduced bend radii and lower room-temperature formability when selecting H3x-style tempers. Hardness correlates with cold work; high-strength tempers show substantially increased hardness and reduced elongation, and thickness has a notable effect as heavy sections tend to have slightly lower effective hardening after processing.

Resistance to cyclic corrosion fatigue and stress-corrosion cracking is superior to many Cu-bearing alloys, making 5059 attractive in welded marine structures. Thickness and temper both influence fatigue endurance; thicker members provide more load distribution but can be more challenging to fully strain-harden in production.

Property	O/Annealed	Key Temper (H116 / H36 range)	Notes
Tensile Strength	~220–300 MPa	~400–480 MPa	Wide range depends on degree of strain hardening and stabilization
Yield Strength	~100–170 MPa	~350–420 MPa	High-strength tempers provide exceptional yield for non-heat-treatable Al
Elongation	~18–26%	~6–12%	Annealed is highly ductile; hardened tempers trade ductility for strength
Hardness (HB)	~55–75 HB	~120–150 HB	Hardness rises with amount of cold work and stabilization treatment

Physical Properties

Property	Value	Notes
Density	~2.66 g/cm³	Typical for Al–Mg alloys; lower than steel enabling weight savings
Melting Range	Solidus ~555–620 °C; Liquidus up to ~650–660 °C	Alloying shifts solidus below pure Al liquidus; useful for casting considerations
Thermal Conductivity	~130–160 W/(m·K)	Lower than pure Al but still favorable for thermal management compared to steels
Electrical Conductivity	~28–40 %IACS	Reduced from pure Al due to Mg and alloying; adequate for many conductive applications
Specific Heat	~900 J/(kg·K)	Similar to other aluminum alloys, effective for thermal mass design
Thermal Expansion	~23–24 ×10^-6 /K (20–100 °C)	Typical aluminum coefficient; must be considered in dissimilar-metal assemblies

The physical property package makes 5059 attractive where a low-density, thermally conductive metal is needed alongside high strength and corrosion resistance. Thermal conductivity and electrical conductivity are lower than pure aluminum but still much higher than steels, enabling lighter designs in heat-sinking and power distribution applications.

Melting and solidus characteristics are relevant for welding and fusion-based joining; the alloy’s solidification behavior and susceptibility to hot cracking are influenced by minor elements and must be managed by joint design and filler selection.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6.0 mm	Uniform in thinner gauges; cold-workable	O, H111, H116	Widely used for panels, hull plating, and formed components
Plate	6–80+ mm	Slightly reduced work-hardening efficiency in heavy gauges	H116, H36	Structural plates for marine and transport where high yield is required
Extrusion	Profiles up to large cross-sections	Strength depends on extrusion rate and post-stretch	O, H111, H116	Complex profiles for structural frames and fittings
Tube	Diameters varied, wall thickness variable	Strength similar to sheet when cold-drawn	O, H116	Used for structural tubing in corrosive environments
Bar/Rod	Diameters up to 300 mm	Good tensile/yield depending on temper	O, H116, H36	Machined fittings and forged components

Manufacturing route affects final property balance: rolled sheet and plate are commonly stabilized to retain strength after welding, whereas extruded profiles may be solution-homogenized and stretched to control residual stresses. Plate and heavy-gauge products can be more difficult to homogeneously cold-work, requiring tailored processes to achieve target strengths.

Typical applications for each form reflect trade-offs between manufacturability and final performance: sheet for formed panels and hull plating, plate for welded structural members, extrusions for precision fittings and rails, and bar/rod for machined parts that exploit the alloy’s strength and corrosion resistance.

Equivalent Grades

Standard	Grade	Region	Notes
AA	5059	USA	Primary Aluminum Association/AA designation
EN AW	5059	Europe	EN AW-5059 is the common European designation, similar chemistry and tempers
JIS	A95059 (approx)	Japan	Local designations map to UNS/AA with some differences in impurity limits
GB/T	Al–Mg5.5–Cr (approx)	China	Chinese standards may use nominal composition names rather than AA numbers

Standards across regions are broadly harmonized for 5xxx alloys, but there are subtle differences in maximum impurity limits, exact magnesium windows, and specified mechanical testing conditions. These variations can lead to small differences in guaranteed tensile/yield values and corrosion performance for supplied material.

When sourcing internationally, check the mill certs and procurement specifications for exact compositional limits, temper definitions, and mechanical test requirements to ensure interchangeability for critical structural applications.

Corrosion Resistance

5059 exhibits excellent atmospheric corrosion resistance and is particularly robust in marine and chloride-laden environments. The high magnesium content promotes a protective oxide film and helps maintain passive behavior; added chromium and controlled copper keep susceptibility to localized pitting and SCC low.

In marine behavior testing 5059 typically outperforms many 6xxx and 7xxx series alloys that contain higher copper or zinc levels; it also shows improved resistance relative to some lower‑Mg 5xxx alloys under long-term salt spray and immersion conditions. Galvanic compatibility is favorable when coupled to stainless steels, titanium, or compatible aluminum alloys, but designers must still ensure insulating measures when pairing with more noble metals like copper or brass.

Stress‑corrosion cracking (SCC) resistance is a significant advantage for 5059 compared with Cu-bearing high‑strength alloys; however, high cold-work temper and corrosive tensile stresses can still drive SCC in severe environments. Welded assemblies must be designed to avoid tensile stresses in the HAZ and to use compatible filler metals and post‑weld treatments where applicable.

Fabrication Properties

Weldability

5059 is readily welded using common fusion processes such as TIG (GTAW) and MIG (GMAW) with good joint performance when proper filler metals are used. Recommended fillers for many 5xxx applications include AlMg4.5Mn (5183) or AlMg5 (5356 depending on application), chosen to control ductility and corrosion resistance in the weld metal. Hot-cracking risk is lower than for many 6xxx and 7xxx alloys, but HAZ softening occurs and joint design should account for reduced local strength after welding.

Machinability

Machinability is moderate to fair; the alloy is not the easiest to machine due to its tendency to produce continuous, sometimes gummy chips at lower cutting speeds. Carbide tooling with positive rake and aggressive chip breakers, plus high feed rates and good coolant/lubrication, improve productivity. Surface finish and tool life are sensitive to temper and section size, so machining parameters should be tailored to the specific temper supplied.

Formability

Formability is excellent in the O temper and declines as the temper is strengthened by cold work. Bend radii should follow conservative guidelines in hardened tempers; annealing before forming is a common practice for complex shapes. Best forming results come from O or lightly worked tempers and from using controlled bending and stretch-forming techniques rather than aggressive stamping on high‑strength tempers.

Heat Treatment Behavior

5059 is fundamentally a non-heat-treatable alloy; it does not develop peak hardness through solution treatment and artificial aging like 6xxx-series alloys. Attempts at traditional solution-and-aging cycles will not produce the same strengthening mechanisms because Mg remains in solid solution and strengthening is not dominated by precipitate hardening.

Strength adjustments are achieved by thermomechanical processing and work hardening, followed by stabilization treatments (e.g., mild heat stabilization or controlled stretching) to lock-in desirable dislocation structures. Annealing (O) returns the alloy to a fully soft state, enabling forming operations, while controlled cold work increases strength at the expense of ductility.

For welded structures, localized temper changes in the HAZ can reduce strength; post-weld heat treatment is generally not a route to regain original properties and designers should plan for mechanical design margins or localized mechanical reworking where needed.

High-Temperature Performance

5059 retains useful strength up to moderate temperatures but experiences progressive strength loss above approximately 100 °C under continuous service. Short-term exposure at elevated temperatures (up to ~150 °C) is tolerated, but long-term elevated-temperature exposure accelerates softening and may reduce creep resistance.

Oxidation is limited due to the protective aluminum oxide, but elevated temperatures can alter surface chemistry and accelerate galvanic interactions with dissimilar metals. In the HAZ, elevated welding temperatures can lead to localized over-aging-type softening and microstructural coarsening that reduce fatigue and yield properties.

Designers should limit continuous service temperature to conservative values when high strength retention is required, and should validate joint and fastener-related creep/fretting behavior for applications with sustained loads at elevated temperatures.

Applications

Industry	Example Component	Why 5059 Is Used
Marine	Hull plating and deck structures	High strength-to-weight with excellent seawater corrosion resistance
Offshore / Energy	Platform structural members	Resistance to SCC and chloride corrosion in welded assemblies
Aerospace / Defense	Fittings and structural brackets	High yield and toughness where corrosion resistance is essential
Transportation	Lightweight structural rails and bodies	Weight reduction with superior strength and weldability
Electronics / Thermal	Chassis and heat spreaders	Adequate thermal conductivity combined with structural integrity

5059 is selected for components that must survive harsh environments while minimizing weight and permitting welding and fabrication at production scale. Its combination of strength, corrosion resistance, and fabricability makes it a preferred alloy for demanding marine and structural applications where long service life and joint reliability are priorities.

Selection Insights

Choose 5059 when you need a high-strength, non-heat-treatable aluminum with marine-grade corrosion resistance and good weldability. It is well suited for welded structural components where long-term exposure to chlorides is expected.

Compared with commercially pure aluminum (e.g., 1100), 5059 trades conductivity and extreme formability for much higher strength and superior corrosion resistance; use 1100 only when electrical/thermal conductivity or maximum ductility is the primary requirement. Compared with common work-hardened alloys like 3003 or 5052, 5059 sits higher in strength while offering comparable or better marine corrosion resistance, though it is costlier and less formable in hardened tempers. Compared with heat-treatable alloys such as 6061/6063, 5059 is often preferred where welded corrosion performance and SCC resistance matter more than absolute peak strength.

When specifying, weigh the trade-offs among strength, formability, and cost: pick annealed or lightly worked tempers for forming, and stabilized strain-hardened tempers for structural members. Verify availability from mills for required thicknesses and tempers, and confirm qualified filler metal and welding procedures for critical joints.

Closing Summary

5059 remains a relevant and technically attractive aluminum alloy for modern engineering where a balance of high non-heat-treatable strength, weldability, and superior marine corrosion resistance is required. Its alloy chemistry and processing options provide designers with a practical way to reduce weight while maintaining long-term structural integrity in harsh environments.