Aluminum Scalmalloy (Al-Mg-Sc-Zr): Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Scalmalloy is a proprietary Al-Mg-Sc-Zr family alloy developed for high-performance applications where a combination of high specific strength and good fracture toughness are required. It does not sit in a classical 2xxx/3xxx/5xxx/6xxx/7xxx series designation because it is a modern, alloyed aluminum concept targeted at additive manufacturing and specialized wrought forms; it is most often described as an Al-Mg-Sc-Zr alloy rather than a single AA series number.

The major alloying elements are magnesium (Mg) for solid solution strengthening and lower density, scandium (Sc) and zirconium (Zr) for fine, coherent Al3(Sc,Zr) dispersoid precipitation, and trace control of iron, silicon and other residuals. Strengthening is primarily by precipitation hardening from Al3Sc and Al3(Sc,Zr) dispersoids that nucleate and pin grain boundaries; work-hardening contributes in some wrought tempers but the defining mechanism is heat-treatable precipitation strengthening.

Key traits include very high strength-to-weight ratio relative to conventional aluminum alloys, improved grain refinement and recrystallization resistance from Sc/Zr dispersoids, good fatigue properties, and competitive corrosion resistance compared with typical high-strength alloys. Formability and weldability can be excellent in annealed or appropriately processed tempers, but require careful control to preserve dispersoid structure; these factors make Scalmalloy attractive to aerospace, motorsport, high-end automotive, and additive-manufacturing-driven industries.

Engineers choose Scalmalloy when design drivers prioritize peak specific strength, stable microstructure during elevated-temperature processing, and resistance to grain coarsening. It is often selected over conventional 6xxx and 7xxx alloys when a designer needs better microstructural stability, superior fatigue life, or when additive manufacturing enables complex geometries that benefit from the alloy’s powder metallurgy behavior.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility for forming
H14	Medium	Moderate	Good	Good	Work-hardened, increased yield with retained formability
T5	Medium-High	Moderate	Good	Good	Cooled from hot working and artificially aged
T6	High	Low-Moderate	Fair	Good	Solution treated, quenched and artificially aged to peak strength
T651	High	Low-Moderate	Fair	Good	Stress-relieved after solution and aging; used for critical dimensions
AM-As-Built (no suffix)	Variable	Variable	Limited	Variable	Additive-manufactured state; properties depend on process and post-treatment

Tempering strongly affects Scalmalloy by controlling the size, density and distribution of Al3(Sc,Zr) dispersoids and any Mg-rich precipitates. Annealed O temper maximizes ductility and formability but sacrifices most of the precipitation-strengthened performance that defines Scalmalloy’s advantage.

Heat treatments such as T5/T6 increase yield and tensile strength via controlled nucleation and growth of nanoscale Al3(Sc,Zr) particles; overaging reduces peak strength but can improve toughness and resistance to stress-corrosion phenomena. For additively manufactured material, in-situ thermal cycles and tailored post-process aging can produce properties matching or exceeding wrought T6 equivalents.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.4 (typical)	Controlled low Si to avoid brittle intermetallics; may vary for powder production
Fe	≤ 0.6 (typical)	Kept low to limit coarse intermetallic particles that reduce toughness
Mn	≤ 0.2	Minor, typically low in Scalmalloy; helps in grain structure control if present
Mg	~3.0–6.0	Principal strength and density-reducing element; participates in solid solution and potential Mg-rich precipitates
Cu	≤ 0.2	Low copper content to avoid excessive corrosion susceptibility and hot cracking
Zn	≤ 0.25	Low zinc to avoid stress-corrosion cracking tendencies
Cr	≤ 0.1	Typically low; controlled to avoid unwanted phases
Ti	≤ 0.1	Trace levels sometimes used to refine grains in powder metallurgy
Others (Sc, Zr)	Sc ~0.1–0.7, Zr ~0.05–0.25	Sc and Zr are the signature elements producing stable Al3(Sc,Zr) dispersoids

The relatively modest Mg content provides solid-solution strengthening and lowers density relative to pure aluminum, while the scandium and zirconium additions form coherent L12 Al3(Sc,Zr) dispersoids that pin dislocations and grain boundaries. Control of impurities such as iron and silicon is critical because coarse intermetallic particles will erode fatigue performance and negate some benefits of the nanoscale dispersoids.

Sc and Zr also dramatically improve recrystallization resistance, enabling retention of fine microstructures during hot working or additive manufacturing; this contributes directly to improved yield, toughness and fatigue life compared with Mg-only alloys.

Mechanical Properties

Scalmalloy exhibits high tensile strength with a relatively high yield-to-tensile ratio compared with many conventional aluminum alloys, and this behavior is strongly dependent on temper and processing route. Peak-aged tempers (T6-like) produce the highest UTS and yield strengths via dense Al3(Sc,Zr) dispersoids, while annealed tempers yield significantly higher elongation and forming capability. Fatigue resistance is typically excellent for its strength class due to refined grains and a homogeneous dispersion of nanoscale particles that reduce crack initiation sites.

Hardness correlates with precipitate density and age condition; Vickers hardness in peak-aged material is elevated and shows good retention after thermal exposure relative to many Al-Mg or Al-Zn-Mg alloys. Thickness and build method (wrought sheet vs additive powder) affect properties; thicker sections may show slightly lower peak strength due to slower cooling and coarsening tendencies unless Zr content or post-processing is optimized. Corrosion and stress-corrosion cracking resistance are generally favorable but must be verified relative to specific service environments because high-strength conditions trade some ductility for strength.

Property	O/Annealed	Key Temper (e.g., T6)	Notes
Tensile Strength (UTS)	~200–320 MPa	~420–560 MPa (typical range)	Wide range depending on processing; AM variants can exceed wrought values
Yield Strength	~90–220 MPa	~350–480 MPa (typical range)	Yield increases markedly with precipitation and work-hardening
Elongation	~18–35%	~6–15%	Peak tempers reduce elongation; annealed states provide formability
Hardness (HV)	~40–80 HV	~120–180 HV	Hardness corresponds with precipitate density and age condition

Physical Properties

Property	Value	Notes
Density	~2.68 g/cm³	Slightly below pure Al due to Mg; value varies with composition
Melting Range	Solidus ≈ 580–610 °C; Liquidus ≈ 640–660 °C	Approximate alloy-dependent range; heat treatments use temperatures below solidus
Thermal Conductivity	~100–150 W/m·K	Lower than pure Al due to alloying; good for many thermal management roles
Electrical Conductivity	~30–45 % IACS	Reduced relative to pure Al because of Mg and dispersoids
Specific Heat	~0.88–0.92 J/g·K (≈880–920 J/kg·K)	Typical of aluminum alloys near room temperature
Thermal Expansion	~23–25 ×10⁻⁶ /K	Coefficient similar to common aluminum structural alloys

The physical properties make Scalmalloy attractive where specific stiffness and thermal performance are needed with reduced mass penalty. Density and thermal expansion are comparable to other Al-Mg alloys, enabling compatibility with many aluminum-based systems and joints without excessive differential expansion.

Thermal conductivity remains adequate for heat-spreading applications, though designers should account for reduced conductivity relative to pure aluminum and consider surface coatings or design geometry to optimize thermal paths when used as heat sinks.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Good uniformity in thin gauges	O, T5, T6	Widely used for panels and formed structures; tempering controls formability
Plate	>6 mm	Strength can vary with thickness	T6, T651	Thick plates require careful heat treatment to avoid coarse precipitates
Extrusion	Complex profiles, various sizes	Excellent when homogenized	T5, T6	Longitudinal grain control and recrystallization resistance aid extrudability
Tube	OD variable, thin- to thick-wall	Similar to extruded behavior	T5, T6	Used for structural tubes and pressure-type components
Bar/Rod	Diameters up to large sections	Good machinability in annealed state	O, Hxx, T6	Bars used for machined fittings and fasteners
Powder / Additive (AM)	Powder particles 15–60 µm; AM builds variable	As-built can be optimized to high strengths	AM-As-Built, T5/T6 post-ages	Scalmalloy is widely used in powder form for LPBF/EBM additive processes

Differences in processing directly affect microstructure and thus mechanical behavior; additive-manufactured forms may require tailored post-build heat treatments to realize full precipitation strengthening, whereas wrought plate and extrusions rely on conventional solution and aging cycles. Product form selection is driven by geometry, surface finish, dimensional tolerance and whether high-temperature processing steps (e.g., extrusion homogenization or AM thermal cycles) are available to stabilize dispersoid structures.

The powder metallurgy route is a key differentiator for Scalmalloy, enabling complex geometries, high build efficiencies and microstructures that are difficult to achieve with traditional casting or wrought routes; designers should specify both form and post-process to ensure targeted properties.

Equivalent Grades

Standard	Grade	Region	Notes
AA	Scalmalloy (Al-Mg-Sc-Zr)	USA	Proprietary alloy; not an official AA series designation
EN AW	Not standardized / proprietary	Europe	Typically supplied as proprietary alloy designations or customer-specific specs
JIS	No direct equivalent	Japan	No standard JIS grade; similar performance compared to high-strength Al-Mg-Sc alloys
GB/T	Proprietary / experimental grades	China	Local producers may offer Sc-Zr-Mg alloys but exact composition and temper vary

There are no direct one-to-one equivalents to Scalmalloy in conventional published standards because the alloy is proprietary and optimized for powder-based processes and alloying with scandium. European and Asian suppliers often list Sc-containing alloys as proprietary grades or experimental designations rather than standardized AW numbers.

When comparing to standards, engineers should treat Scalmalloy as a distinct family and verify chemical and mechanical property certificates from suppliers; substitution requires careful consideration of dispersoid content and processing history rather than simple element-for-element matching.

Corrosion Resistance

Scalmalloy generally offers good atmospheric corrosion resistance similar to or better than many high-strength aluminum alloys because the fine, homogeneous microstructure limits localized galvanic sites and coarse intermetallics. In neutral and mildly corrosive atmospheres it performs well, particularly when properly aged and surface-treated; anodizing or conversion coatings further enhance surface protection.

In marine chloride environments, Scalmalloy exhibits reasonable pitting resistance relative to high-strength 7xxx alloys, but it is not as inherently resistant as certain 5xxx magnesium-containing alloys designed specifically for seawater exposure. Designers should account for possible localized attack in stagnant or crevice-prone regions and specify appropriate coatings or cathodic protection where exposure is severe.

Stress-corrosion cracking susceptibility is typically lower than that of high-strength Al-Zn-Mg (7xxx) families because Sc/Zr dispersoids reduce grain boundary precipitation and make crack propagation more difficult. Galvanic interactions follow standard aluminum behavior; Scalmalloy remains anodic to stainless steels and copper alloys, so insulating contacts or sacrificial protection should be considered in mixed-metal assemblies.

Fabrication Properties

Weldability

Welding Scalmalloy is feasible with TIG and MIG techniques when weld procedures control heat input and filler compatibility. Recommended filler alloys are typically Al-Mg-based or specially formulated Sc-containing fillers if available, to avoid large compositional mismatch and to maintain ductility in the joint. Weld heat-affected zones (HAZ) can exhibit softening if dispersoids coarsen or precipitate distributions are altered, so post-weld artificial aging or localized heat treatments are often used to restore properties. Hot-cracking risk is moderate; low copper and controlled silicon help reduce susceptibility compared to some Al-Zn alloys.

Machinability

Machinability in annealed conditions is similar to other medium-strength aluminum alloys and is generally favorable with sharp carbide tools, moderate feeds and higher cutting speeds. In peak-aged or high-strength tempers, increased hardness can raise tool wear rates and requires more robust tooling and reduced depth-of-cut to maintain surface finish. Chip formation is typically continuous and ductile; coolant is recommended to control built-up edge and chip welding on tools. Tool materials like carbide or polycrystalline diamond offer good life on high-volume CNC operations.

Formability

Cold formability is best in O or H tempers where elongation is highest; minimum bend radii should follow standard aluminum guidelines, typically 2–3× material thickness for small-radius bends in annealed sheet. Peak-aged tempers reduce elongation and increase springback, so forming should be performed in softer tempers followed by solution and aging if final strength is required. Warm forming and incremental sheet forming techniques benefit from Scalmalloy’s recrystallization resistance, enabling complex shapes with finer microstructure retention. For deep drawing, pre-aging to a medium-strength condition often balances formability and final property needs.

Heat Treatment Behavior

Scalmalloy is heat-treatable and responds primarily to solution treatment followed by quenching and artificial aging to produce a dense distribution of Al3(Sc,Zr) dispersoids. Typical solution treatment temperatures are in the range of approximately 500–540 °C with quenching to retain supersaturation of solutes; subsequent artificial aging at 200–300 °C for several hours generates peak hardness and strength. Zr additions slow coarsening of Al3Sc precipitates, widening the aging window and improving thermal stability relative to Sc-only alloys.

Because Al3(Sc,Zr) precipitates are coherent and highly stable, Scalmalloy exhibits less overaging sensitivity than many conventional Al-Mg or Al-Zn-Mg alloys, but extended exposure at elevated temperatures will eventually grow precipitates and reduce peak-strength. For additive-manufactured material, in-situ thermal cycles can induce partial precipitation during build, and a short solution or direct aging cycle post-build frequently yields optimized mechanical properties without full high-temperature solution treatment. Work-hardening can be used to raise strength in non-heat-treated tempers, and annealing returns the material to a ductile condition for forming or joining.

High-Temperature Performance

Scalmalloy maintains useful strength at moderately elevated temperatures compared with many aluminum alloys because Al3(Sc,Zr) dispersoids resist coarsening and continue to impede dislocation motion. Strength retention is typically acceptable up to approximately 200–250 °C for long-term service, with progressive softening above this range as precipitate coarsening and matrix recovery occur. Short-term excursions to higher temperatures (up to ~300 °C) may be tolerated without catastrophic loss, but designers should avoid sustained exposure at those levels unless validated by long-term testing.

Oxidation is typical of aluminum alloys; protective oxide layers form rapidly at elevated temperatures but do not prevent structural property changes due to precipitate coarsening. The HAZ around welds and locally heated zones can show reduced strength and should be assessed for creep or relaxation under service loads at elevated temperatures.

Applications

Industry	Example Component	Why Scalmalloy (Al-Mg-Sc-Zr) Is Used
Automotive	Structural brackets, suspension components	High specific strength and fatigue resistance reduce mass and improve durability
Marine	Structural fittings, small craft components	Good strength-to-weight and reasonable corrosion resistance in chloride environments
Aerospace	Fittings, brackets, lightweight structural parts	Exceptional strength-to-weight and thermal stability for critical, lightweight parts
Motorsports	Roll cages, chassis components	Allows aggressive weight saving with retained crashworthiness
Electronics	Lightweight heat spreaders, structural frames	Balance of thermal conductivity and stiffness with lower mass
Additive Manufacturing	Complex structural prototypes and production parts	Alloy optimized for powder bed fusion with high achievable mechanical properties

Scalmalloy’s combination of high strength, stability during thermal processing, and powder metallurgy friendliness makes it valuable across sectors where lightweight, complex-shaped components are required. Its use in additive manufacturing has extended design freedom while enabling performance that rivals or exceeds many conventionally produced high-strength aluminum alloys.

Selection Insights

Choose Scalmalloy when designers need high specific strength and excellent fatigue resistance, and when manufacturing methods (wrought or additive) and budgets allow for a Sc-containing alloy. It is best selected where weight savings, microstructural stability, and retention of fine grains through hot-working or AM thermal cycles are primary requirements.

Compared with commercially pure aluminum (e.g., 1100), Scalmalloy trades electrical and thermal conductivity and superior formability for far higher strength and better fatigue performance; use Scalmalloy where structural efficiency outweighs maximum conductivity. Versus common work-hardened alloys such as 3003 or 5052, Scalmalloy delivers substantially greater strength with comparable or better fatigue life, though sacrificial corrosion resistance of some 5xxx series in certain marine environments may be superior. Compared with common heat-treatable alloys like 6061 or 6063, Scalmalloy often provides superior thermal stability and microstructural control; it is preferred when long-term high-strength retention and microstructure stability in complex or additively manufactured parts are required despite potential cost and availability trade-offs.

Closing Summary

Scalmalloy (Al-Mg-Sc-Zr) remains relevant because it uniquely combines precipitation-stabilized microstructures with excellent strength-to-weight and fatigue characteristics, and it adapts well to modern manufacturing routes such as additive manufacturing and advanced wrought processing. Its tailored chemistry of Mg, Sc and Zr provides designers a durable, high-performance aluminum solution for demanding structural applications where conventional alloys cannot meet the combined requirements of strength, stability and formability.