Aluminum 6042: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 6042 is a member of the 6xxx series of aluminum alloys, which are primarily Al-Mg-Si systems amenable to precipitation hardening. Its chemistry places it among heat-treatable, medium-strength structural alloys that balance strength, extrudability and surface finish for architectural and engineering uses.

The principal alloying elements in 6042 are magnesium and silicon, which form Mg2Si precipitates during heat treatment to provide age-hardening strengthening. Secondary additions such as copper and trace elements (Cr, Mn, Ti) are used to refine grain structure, improve response to aging, and control recrystallization during thermomechanical processing.

6042 delivers a combination of moderate to high strength (especially in T6-type tempers), good corrosion resistance in atmospheric and mildly marine environments, and acceptable weldability when proper filler metals and post-weld practices are used. Typical industries are automotive, architectural curtain wall and façade systems, pressure vessels, general structural extrusions, and some aerospace secondary structures where a good strength-to-weight ratio and surface finish are required.

Engineers select 6042 when they need a more flagrant strength and age-hardening response than 5xxx/3xxx work-hardened alloys, but where the extreme peak strengths of 7xxx series are unnecessary or would compromise toughness and weldability. The alloy is often chosen over 6061/6063 when specific extrusion surface finish, age-hardening curve or availability drive the decision, and it can be preferred for formed extrusions with post-form heat treatment to regain strength.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (>15–25%)	Excellent	Excellent	Fully annealed condition for maximum formability
H14	Medium	Moderate (8–12%)	Good	Good	Strain-hardened for moderate strength, limited forming
T5	Medium-High	Moderate (8–12%)	Moderate	Good	Cooled from hot working and artificially aged
T6	High	Lower (6–12%)	Fair to Poor	Good (with filler)	Solution treated and artificially aged for peak strength
T651	High	Lower (6–12%)	Fair to Poor	Good (with filler)	Solution treated, stress-relieved by stretching, artificially aged

The temper chosen for 6042 strongly dictates the trade-off between formability and strength. Annealed O tempers are used when deep drawing or complex bends are required, while T5/T6 variants are selected when dimensional stability and peak mechanical properties matter.

During welding and local heating, the heat-affected zone can exhibit softening for T6 or peak-aged tempers, so temper selection often considers whether post-weld heat treatment or mechanical stress relief will be applied. H-series tempers give intermediate options for production parts that require some forming after initial tempering or that are produced by cold work.

Chemical Composition

Element	% Range	Notes
Si	0.6–1.3	Controls Mg2Si precipitate amount and influences fluidity in casting and extrusion surface finish
Fe	≤0.7	Impurity element; higher levels can form intermetallics that reduce ductility and surface quality
Mn	0.15–0.45	Grain structure control and strength contribution through dispersoids
Mg	0.7–1.2	Primary strengthening element; combines with Si to form Mg2Si precipitation hardening phases
Cu	0.15–0.35	Raises strength and can accelerate aging; excessive Cu may reduce corrosion resistance
Zn	≤0.2	Minor influence; kept low to avoid undesired strength/embrittlement effects
Cr	0.05–0.25	Controls grain structure and recrystallization during thermal processing
Ti	≤0.15	Used as grain refiner in castings and prime stock production
Others	Balance Al; residuals ≤0.15 each	Balance is aluminum with allowable residuals and trace elements

The Mg and Si contents determine the volume fraction and kinetics of Mg2Si precipitates, which are the primary hardening phases in 6042. Minor additions such as Cr and Mn form dispersoids that pin grain boundaries and improve toughness and stability during thermomechanical processing, while Cu can be used to modify the aging curve and increase peak strength at the expense of some corrosion resistance.

Impurity elements like Fe and Zn are tightly controlled because they form intermetallic particles that harm surface finish, decrease ductility and can initiate localized corrosion. The overall balance between these elements and the thermomechanical history governs attainable properties and processing windows.

Mechanical Properties

Tensile behavior of 6042 is characteristic of heat-treatable Al-Mg-Si alloys: low strength and high elongation in the annealed condition, with pronounced increases in yield and ultimate tensile strength after solutionizing and artificial aging. The yield-to-tensile ratio typically tightens after precipitation hardening, giving predictable elastic performance for structural design. Elongation in aged tempers commonly drops relative to O-condition values but usually remains adequate for many structural applications.

Hardness correlates strongly with temper and aging condition; the T6-type peak-aged condition shows a clear rise in Brinell/Vickers hardness concurrent with strength gains. Fatigue performance depends on surface finish, loading frequency and mean stress, and aged tempers often offer improved fatigue strength over annealed material but can be sensitive to notches and welds. Thickness and section geometry influence cooling rates during quenching and aging; heavy sections may not reach full peak hardness without specialized heat-treatment cycles.

Designers must account for the possibility of overaging in service at elevated temperatures, and they should consider the effects of forming or welding which can locally alter the precipitation state and thus mechanical performance. For high-reliability applications, validated process control on aging and post-fabrication inspection are recommended.

Property	O/Annealed	Key Temper (e.g., T6)	Notes
Tensile Strength	~120–200 MPa	~250–340 MPa	Values are typical ranges depending on section thickness and aging schedule
Yield Strength	~60–120 MPa	~200–300 MPa	Yield increases markedly after artificial aging; design using conservative lower bound
Elongation	~15–25%	~6–14%	Elongation drops with increasing strength; thicker samples often show higher ductility
Hardness (HB)	~35–65 HB	~75–110 HB	Hardness tracks tensile strength; measurement method and sample preparation influence values

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for Al-Mg-Si alloys; useful for weight-critical designs
Melting Range	~555–650 °C	Solidus-liquidus range may vary with exact composition and impurities
Thermal Conductivity	~150–170 W/(m·K)	Lower than pure Al due to alloying; still good for thermal management
Electrical Conductivity	~35–45 %IACS	Alloying reduces conductivity compared with pure aluminum
Specific Heat	~0.9 J/(g·K)	Approximate value near room temperature (900 J/(kg·K))
Thermal Expansion	~23–24 µm/(m·K)	Typical coefficient of thermal expansion for 6xxx series alloys

The density and thermal properties of 6042 make it attractive where weight savings and heat dissipation are important, such as in heat sinks and exteriors requiring both structure and thermal management. Thermal conductivity is lower than pure aluminum but remains sufficiently high for many electronic or heat-exchanging applications.

Electrical conductivity is reduced by alloying and should be considered when specifying 6042 for electrical applications; if maximum conductivity is required, purer alloys (e.g., 1100) or copper may be preferable. The thermal expansion coefficient is similar to other Al-Mg-Si alloys and should be accommodated in multi-material assemblies.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Thin-gauge parts reach solution and age response quickly	O, H14, T5, T6	Used for panels, enclosures, and decorative façades
Plate	6–100+ mm	Thick sections may require specialized heat treatment to homogenize	O, T6 (limited)	Heavy structural parts and fabricated pressure components
Extrusion	Complex cross-sections, up to large profiles	Good response to extrusion with controlled precipitate distribution	T5, T6, T651	Widely used for architectural and structural extrusions
Tube	1–20 mm wall; various diameters	Welded or seamless tubing; properties depend on forming route	O, T6	Structural tubing and heat-exchanger cores
Bar/Rod	Diameters up to 200 mm	Bulk sections show thickness-dependent aging	O, T6	Machined components and fasteners for lower-volume parts

Sheets and extrusions are the most common product forms for 6042 because the alloy extrudes well to tight surface finish requirements and responds predictably to artificial aging. Plate and heavy sections can be produced but require careful control of solution-treatment and quench cycles to avoid soft cores or inconsistent properties through the thickness.

Extruded profiles often receive T5 or T6 treatments after extrusion to achieve dimensional stability and required strength, whereas sheet rolling schedules aim for flatness and surface quality with subsequent aging as needed.

Equivalent Grades

Standard	Grade	Region	Notes
AA	6042	USA	Aluminum Association designation for this alloy
EN AW	EN AW-6042	Europe	EN designation equivalent; chemical and mechanical specs align closely with AA 6042
JIS	Closest: A6061	Japan	No exact 1:1 JIS counterpart; A6061 family is often substituted with process adjustments
GB/T	Closest: 6061/6063 family	China	Direct 6042 equivalent may not be standardized; 6061/6063 alloys are common local substitutes

Standards and minor chemistry tolerances vary between regions; EN AW-6042 is commonly used in Europe and tracks closely with AA 6042 specifications. When substituting from different standards, engineers should verify compositional limits, temper designations and guaranteed mechanical properties since small changes (especially in Cu or Fe limits) can influence aging behavior and corrosion performance.

For cross-border procurement, it is advisable to request mill certificates and specify key properties (e.g., tensile, yield, elongation, and temper) rather than relying solely on nominal grade names. Process history such as extrusion speed, quench medium and aging cycle often affects final properties more than nominal grade alone.

Corrosion Resistance

In atmospheric exposures 6042 forms a protective aluminum oxide film and demonstrates good general corrosion resistance similar to other 6xxx family alloys. It performs well in industrial atmospheres and for architectural applications but can be susceptible to pitting and crevice corrosion in aggressive chloride environments if protective coatings or anodizing are not applied.

In marine or high-chloride environments, 6042 is serviceable with appropriate surface treatments such as anodizing, sealants, or organic coatings; however, austenitic stainless steels or 5xxx series aluminum with higher intrinsic corrosion resistance may be preferred for constant immersion. Stress corrosion cracking risk is moderate and primarily a concern for peak-aged tempers under sustained tensile stress in corrosive media; design mitigation includes temper selection, compressive surface treatments and avoiding high residual tensile stresses.

Galvanic interactions place 6042 anodic when coupled with stainless steels, copper or carbon steel, so electrical isolation, sacrificial anodes or careful joint design is necessary to prevent accelerated corrosion. Compared with 5xxx magnesium-bearing alloys, 6042 generally offers comparable atmospheric corrosion resistance but trades some chloride resistance for better age-hardenability and machinability.

Fabrication Properties

Weldability

6042 is generally weldable by conventional processes such as TIG (GTAW) and MIG (GMAW), and filler alloys in the 4xxx (Al-Si) or 5xxx (Al-Mg) families are commonly used depending on desired weld strength and corrosion resistance. Hot-cracking risk is low to moderate; cleanliness, proper joint design and controlling heat input reduce susceptibility. The heat-affected zone of T6 or peak-aged material typically softens due to dissolution/reprecipitation of Mg2Si, so post-weld aging or local heat treatment may be required to restore strength.

Machinability

Machinability of 6042 is moderate and generally better than many high-strength alloys but not as free-machining as some Al-Si hypereutectic alloys. Carbide tooling with positive rake and high-speed finishing feeds produce excellent surface quality; coolant/cutting-lubricant use is recommended to control built-up edge and chip formation. Typical practice uses higher cutting speeds than steels, modest feed rates and tooling geometries optimized for aluminum to avoid smearing and to maintain dimensional tolerance.

Formability

Forming is best carried out in annealed (O) or partially annealed H-series tempers; cold forming of T6 is limited and springback increases with strength. Minimum bend radii depend on temper and thickness: annealed sheet can often be bent to 1–2× thickness for simple bends, while T6 may require 3–6× thickness or pre-heating/forming prior to final heat treatment. Deep drawing and complex stamping should use O or T4 condition followed by subsequent artificial aging if required for final strength.

Heat Treatment Behavior

As a heat-treatable alloy, 6042 follows the classic solutionizing—quenching—aging sequence to develop peak mechanical properties. Solution treatment typically occurs in the 510–550 °C range to dissolve Mg2Si and homogenize the matrix, followed by rapid quenching (water quench preferred) to retain a supersaturated solid solution. Artificial aging (precipitation heat treatment) is commonly performed at temperatures between ~150–190 °C for several hours to develop T5/T6 hardness and strength levels.

The T5 temper represents cooling from hot working followed by artificial aging without full solution treatment, giving a moderate-strength, stable condition. The T6 temper involves a full solution treatment prior to artificial aging to achieve near-maximum mechanical properties. Overaging reduces strength but increases toughness and resistance to stress-corrosion cracking; process engineers may intentionally overage to balance performance needs.

Non-heat-treatable strengthening is accomplished via work hardening for H-series tempers, where controlled cold deformation increases dislocation density and strength but reduces ductility. Annealing returns the alloy to the O condition by homogenization and recrystallization to restore formability.

High-Temperature Performance

6042 begins to lose a significant fraction of its room-temperature yield and tensile strength at moderately elevated temperatures; notable softening generally occurs above ~120–150 °C depending on prior aging state. For continuous high-temperature structural service, designers typically limit use to temperatures below this range or specify overaged tempers to improve thermal stability.

Oxidation of aluminum is self-limiting and forms a thin protective oxide layer; however, at elevated service temperatures combined with corrosive environments, oxide scale growth and localized attack can accelerate. Heat-affected zones in welded or locally heated parts are particularly susceptible to microstructural changes and reduced mechanical performance, so thermal management and post-heat processes are required for critical applications.

Creep performance is limited compared with high-temperature alloys, and long-term loading at elevated temperatures should be evaluated through creep testing or service-history data. For intermittent exposure, 6042 can tolerate short excursions at higher temperatures if subsequent aging or stress-relief treatments are applied.

Applications

Industry	Example Component	Why 6042 Is Used
Automotive	Extruded body or trim profiles	Good combination of extrudability, surface finish and age-hardened strength
Marine	Structural members and fittings	Corrosion resistance with ability to be anodized and post-formed
Aerospace	Secondary fittings, brackets	Favorable strength-to-weight and predictable heat-treatment response
Electronics	Heat sinks and enclosures	Thermal conductivity and surface finish suitable for heat-dissipation parts

6042 is often specified where a balance of machinability, age-hardened strength and surface appearance are required, making it suitable for visible architectural elements and load-bearing extrusions. Its ability to be extruded to complex profiles and then artificially aged to dimensional stability makes it popular for production parts in multiple industries.

Selection Insights

When selecting 6042, prioritize it for applications that need a medium-high strength age-hardenable aluminum with good extrudability and surface finish. Choose O or H tempers when forming dominates and T5/T6 when final strength and dimensional stability are primary requirements.

Compared with commercially pure aluminum (1100), 6042 sacrifices electrical conductivity and some ease of forming in exchange for substantially higher strength and better structural performance. Against common work-hardened alloys such as 3003 or 5052, 6042 provides higher peak strength and better response to solution-aging but may be somewhat less corrosion-tolerant in aggressive chloride environments. Versus commonplace heat-treatable alloys like 6061/6063, 6042 may be selected for specific extrusion surface finish, vendor availability or particular aging response even if peak strength is comparable or marginally lower; confirm part-level testing where strength margins are tight.

Closing Summary

Alloy 6042 remains a practical choice where a well-balanced combination of age-hardenable strength, good extrudability and acceptable corrosion resistance is required. Its predictable heat-treatment response, machinability and surface qualities sustain its relevance for architectural, automotive and light structural engineering applications.