Aluminum 1N50: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

1N50 is a medium-strength aluminum alloy belonging functionally to the 5xxx series family (Al-Mg class) and is optimized for structural applications where corrosion resistance and weldability are critical. Its principal alloying element is magnesium, typically in the 4.5–5.5 wt% range, with controlled additions of manganese and trace amounts of chromium and silicon to refine grain structure and improve strength. The alloy is non-heat-treatable; primary strengthening is achieved through solid-solution strengthening from magnesium and by strain hardening during cold working. Key traits include a favorable strength-to-weight ratio, excellent atmospheric and marine corrosion resistance, good weldability with minimal post-weld heat treatment requirements, and reasonable formability in softer tempers.

Industries that frequently use 1N50 include marine and shipbuilding, transportation and trailer manufacture, architectural cladding, and certain automotive structural components where fatigue resistance and corrosion performance are required. Designers choose 1N50 over lower-strength, high-conductivity alloys when increased load capacity and localized weld repairs are anticipated. Compared with higher-strength heat-treatable alloys, 1N50 is often selected for larger structural parts where in-service corrosion resistance and the capacity for large forming radii outweigh the need for peak aged strength.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (≥30%)	Excellent	Excellent	Fully annealed condition; best for deep drawing
H12	Low-Medium	Moderate (20–25%)	Good	Excellent	Partially strain-hardened; moderate forming
H14	Medium	Moderate (12–18%)	Good	Excellent	Half-hard; common for moderately loaded panels
H18	High	Low (6–12%)	Fair	Excellent	Full-hard; limited bending, used where stiffness is required
H22	Medium-High	Moderate (10–15%)	Moderate	Excellent	Strain-hardened and partly annealed; balanced properties
H32	Medium-High	Moderate (10–15%)	Moderate	Excellent	Strain-hardened then stabilized; retains strength after welding
H116	Medium-High	Moderate (10–15%)	Moderate	Very Good	Intended for marine-exposure use with controlled recrystallization

Tempers in 1N50 alter mechanical behavior by combining strain hardening with stabilization treatments to preserve strength during subsequent fabrication operations such as welding. Soft O-tempers maximize ductility and formability but have the lowest yield and tensile strengths, while H-tempers trade ductility for higher strength and improved dimensional stability.

Chemical Composition

Element	% Range	Notes
Si	0.10 – 0.40	Controlled low silicon to limit Fe-silicide formation that reduces ductility
Fe	0.20 – 0.60	Typical impurity; high levels reduce toughness and increase crack sensitivity
Mn	0.20 – 0.80	Grain refinement and resistance to recrystallization; improves strength
Mg	4.50 – 5.50	Principal strengthening element providing solid-solution strengthening and corrosion resistance
Cu	0.05 – 0.30	Kept low to preserve corrosion resistance; small additions may boost strength
Zn	0.05 – 0.25	Minor; kept low because higher levels can reduce corrosion resistance
Cr	0.05 – 0.25	Controls grain structure and reduces susceptibility to exfoliation and stress-corrosion
Ti	0.02 – 0.10	Grain refiner, used in cast/ingot metallurgy to control microstructure
Others (each)	≤0.05	Trace elements and residuals; total others limited per specification

The chemistry of 1N50 is tuned to maximize the solid-solution effect of magnesium while keeping elements that promote intermetallic formation at low levels. Manganese and chromium act as microalloying elements to stabilize the microstructure against grain growth and recrystallization during thermal excursions, preserving toughness and resistance to intergranular corrosion.

Mechanical Properties

Tensile behavior of 1N50 exhibits a progressive increase in yield and ultimate tensile strength with strain hardening; the alloy has a relatively flat tensile-elongation trade-off compared with 6xxx-series heat-treatable alloys. In annealed condition the alloy shows long uniform elongation and a pronounced strain-hardening exponent, which is beneficial for forming operations that rely on plastic redistribution. Hardness correlates closely with temper; H‑tempers reach Brinell values that are typically 20–40% higher than O‑temper material, improving bearing strength but reducing bendability.

Fatigue performance in 1N50 benefits from its ductile fracture mode and favorable corrosion resistance; fatigue limit is sensitive to surface finish, welds, and thickness. Thinner sections exhibit higher apparent ductility and slightly higher yield-to-tensile ratios due to constraint effects, while thicker sections may show reduced ductility and potential for localized porosity or segregation from manufacturing if ingot practice is poor. Designers must consider thickness-dependent forming allowances and potential for HAZ softening adjacent to welds when specifying safety factors for cyclic-loaded parts.

Property	O/Annealed	Key Temper (H32/H116)	Notes
Tensile Strength	~170 MPa	~270–300 MPa	H32/H116 values depend on degree of cold work and stabilization
Yield Strength	~60–90 MPa	~200–240 MPa	Yield increases significantly with strain hardening
Elongation	~30–35%	~10–16%	Elongation reduced in harder tempers; depends on thickness
Hardness (HB)	~35–45 HB	~75–95 HB	Hardness increases with cold work; reflected in wear and bearing resistance

Physical Properties

Property	Value	Notes
Density	2.66 g/cm³	Typical for Al-Mg alloys; contributes to high specific strength
Melting Range	~555–650 °C	Solidus/liquidus interval depends on exact Si/Fe content and segregation
Thermal Conductivity	120–140 W/m·K	Lower than pure Al; still adequate for heat-spreading applications
Electrical Conductivity	~35–45 % IACS	Reduced versus pure Al due to solute Mg; varies with temper and processing
Specific Heat	~0.90 kJ/kg·K	Typical aluminum alloy value useful for thermal mass calculations
Thermal Expansion	23–25 µm/m·K (20–100 °C)	Relatively high expansion; design for differential expansion with dissimilar materials

The physical properties make 1N50 attractive where low mass and thermal conduction are needed alongside structural capability. The alloy’s conductivity and heat capacity mean it can be used in moderate thermal-management roles, but designers must account for thermal expansion when joining to steels or composites to avoid stress concentrations during temperature cycles.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3 – 6.0 mm	Strength varies with temper; thinner gauges show improved formability	O, H14, H32, H116	Widely used for panels, enclosures, and skins
Plate	6 – 120 mm	Lower ductility in thick plate; strength varies less with thickness	O, H22, H32, H116	Structural plate for marine and transport frames
Extrusion	Complex cross-sections up to 300 mm	Can be supplied in overaged or strain-hardened conditions	O, H12, H14, H32	Good surface finish; uses include rails and profiles
Tube	Diameters from small to 400+ mm	Cold drawing and aging can adjust dimensional stability	O, H14, H18	Used in hydraulic frames and corrosion-exposed piping
Bar/Rod	Round/hex up to 200 mm	Cold-drawn or hot-rolled; mechanical properties respond to cold work	O, H12, H18	Machining stock and structural pins/bars

Processing differences drive the selection of product form; sheet production involves rolling with tight thickness control and usually results in a fine, worked surface, whereas plate production may include homogenization anneals to minimize centerline segregation. Extrusions allow complex cross-sections but require careful die design for Mg-containing alloys to avoid surface ripples and ensure dimensional tolerances.

Equivalent Grades

Standard	Grade	Region	Notes
AA	1N50	USA	Proprietary or trade designation; chemistry aligns with Al-Mg class
EN AW	~5xxx equivalent	Europe	Approximate equivalent in EN AW 5xxx series; exact match depends on Mg and Mn content
JIS	~A5xxx series	Japan	Comparable to JIS Al-Mg grades used in marine and structural components
GB/T	~5xxx series	China	Local equivalents available with similar Mg ranges and mechanical properties

Equivalent grade entries should be treated as functional approximations; final selection requires cross-referencing chemical and mechanical spec limits in the applicable standard documents. Regional standards may emphasize slightly different impurity limits, grain structure controls, or temper classifications that lead to practical differences in performance, especially for critical marine and aerospace parts.

Corrosion Resistance

1N50 shows excellent general atmospheric corrosion resistance, attributed to the formation of a stable oxide and the beneficial role of magnesium in passive-film formation. In marine environments the alloy performs well, resisting uniform corrosion and showing reasonable resistance to pitting when protected by proper surface finishes and cathodic protection strategies. However, in highly polluted or industrial atmospheres containing chlorides and sulfates, localized corrosion can accelerate unless protective coatings or anodization are applied.

Stress corrosion cracking susceptibility is low to moderate compared with high-strength heat-treatable Al-Zn-Mg alloys; the combination of moderate strength and Mg content means 1N50 is not immune, particularly under tensile residual stresses and elevated temperatures. Galvanic interactions must be considered when coupling 1N50 to cathodic metals like stainless steels and copper alloys; aluminum will corrode preferentially unless electrically isolated or protected. Compared with 3xxx and 1xxx series alloys, 1N50 trades slightly reduced formability for substantially improved strength and comparable or superior corrosion resistance in chloride-exposed service.

Fabrication Properties

Weldability

1N50 is readily welded by common fusion methods such as MIG (GMAW), TIG (GTAW), and resistance welding with low risk of solidification cracking when good practices are followed. Recommended filler alloys are compatibility-focused Al-Mg series fillers (e.g., ER5356 or ER5183 equivalents) to maintain corrosion resistance and mechanical properties in the weld and HAZ. The HAZ may exhibit some softening relative to highly cold-worked parent material, but stabilizing tempers such as H32 and post-weld mechanical finishing minimize distortion and local strength loss.

Machinability

Machining of 1N50 is moderate in difficulty; its ductility can produce long, contiguous chips if tool geometry and feeds are not optimized. Carbide tooling with positive rake and variable helix geometries works well, with typical cutting speeds lower than for 6xxx series due to work-hardening tendency, and elevated feed rates to promote chip breaking. Surface finish and tolerance control are achievable with standard industrial tooling, but allowances for chatter and clamping of thin sections must be designed into the process.

Formability

Forming performance is best in O and light H-tempers, where the alloy supports tight radii and significant plastic elongation without cracking. Minimum bend radii depend on temper and thickness; typical rule-of-thumb radii for sheet in O temper are 1.0–1.5× thickness for air bending, increasing with harder tempers. Cold-work response is predictable and uniform; parts that require high final strength after forming are often formed in O temper and then cold-worked to H‑tempers to reach the target mechanical properties.

Heat Treatment Behavior

As a non-heat-treatable alloy, 1N50 does not gain strength through solution treatment and artificial aging; strength increases are primarily achieved by cold working and mechanical strain hardening. Annealing (full or partial) is used to restore ductility for forming operations: typical full anneal temperatures are in the 350–420 °C range with controlled cooling to avoid excessive grain growth. Stabilization treatments (e.g., H32) apply light reheats or stretching to minimize natural aging and the loss of strength during subsequent thermal cycles, and they help preserve mechanical properties in welded structures.

If thermal excursions occur during fabrication, only temper-based recovery and recrystallization processes will significantly change properties; designers must avoid temperatures that exceed the alloy’s anneal threshold during service or post-processing, as unintended softening reduces yield and fatigue resistance. Post-weld mechanical treatments such as peening or stretch-forming can be used to reintroduce beneficial compressive residual stresses and regain local strength.

High-Temperature Performance

At elevated temperatures (above ~100–150 °C), 1N50 experiences gradual strength reduction due to recovery and accelerated diffusion-controlled processes affecting the Mg solute distribution. Service limits for sustained loading are typically set conservatively below 100 °C to avoid long-term softening and loss of yield capacity. Oxidation is limited to normal aluminum oxide formation at ambient conditions, but prolonged exposure to oxidizing atmospheres at high temperatures can thicken surface oxides and affect thermal contact resistance.

HAZ behavior near welds is a critical consideration for elevated-temperature service because local softening can reduce fatigue life and increase the risk of creep under sustained loads. For short-term thermal excursions or paint-bake cycles used in finishing, 1N50 tolerates moderate temperatures; however, designers must validate dimensional stability and residual stress evolution for components expected to experience significant thermal cycling.

Applications

Industry	Example Component	Why 1N50 Is Used
Automotive	Structural panels, trailer bodies	Good balance of strength, formability, and corrosion resistance for exposed components
Marine	Hull plating, superstructure, deck fittings	Excellent chloride resistance and weldability for shipboard use
Aerospace	Secondary fittings, interior structural elements	High specific strength with good fatigue performance in non-critical primary structures
Electronics	Enclosures, moderate-duty heat spreaders	Thermal conductivity adequate for passive heat-sinking; low weight aids portability

1N50 is widely specified for medium-duty structural applications where exposure to corrosive environments and the need for in-field welding or forming is common. Its combination of corrosion resistance, weldability, and serviceable strength makes it a cost-effective choice for large panels and fabricated assemblies where higher-strength heat-treatable alloys are unnecessary.

Selection Insights

When selecting 1N50 for a component, prioritize scenarios that require a combination of corrosion resistance, weldability, and moderate-to-high structural strength without the need for precipitation hardening. Choose annealed O for complex forming operations and switch to H-tempers after forming if higher yield strength is required.

Compared with commercially pure aluminum (1100), 1N50 offers substantially higher strength at the cost of modestly reduced electrical conductivity and slightly reduced deep-draw formability. Compared with work-hardened alloys such as 3003 or 5052, 1N50 generally sits at a higher strength level with comparable or better marine corrosion resistance due to its optimized Mg content and microalloying additions. Versus heat-treatable alloys like 6061 or 6063, 1N50 lacks the peak aged strength those materials can achieve, but it is preferred when superior weldability, in-service corrosion performance, and cost-effective large-structure fabrication are the overriding design drivers.

Closing Summary

1N50 remains relevant as a versatile Al-Mg structural alloy that balances strength, corrosion resistance, and fabrication friendliness for marine, transportation, and general structural engineering uses. Its non-heat-treatable metallurgy simplifies manufacturing and repair workflows while delivering the mechanical reliability required for many modern lightweight structural systems.