Alloying Elements in Die-Cast Aluminum

Giới thiệu

Chết đúc imposes very specific constraints: Làm đầy nhanh, tốc độ làm mát cao, các phần mỏng, and extreme sensitivity to entrained gases, oxides and intermetallics.

Design drivers typically include: Khả năng đúc tường mỏng, độ chính xác chiều, static strength, Hiệu suất mệt mỏi, kháng ăn mòn, wear resistance and thermal stability.

Alloying determines the melting/solidification behavior and final microstructure, and therefore underpins every one of these drivers.

Understanding individual element effects and their interactions is essential for metallurgically sound alloy choices.

Die-cast aluminum alloys are engineered based on pure aluminum (a lightweight metal with a specific gravity of ~2.7 g/cm³), which inherently exhibits low mechanical strength, poor castability, and limited wear resistance,

making it unsuitable for structural or functional components in automotive, Không gian vũ trụ, thủy lực, và các ngành công nghiệp điện tử.

To overcome these limitations, key alloying elements are strategically added to tailor the alloy’s microstructure, casting behavior, and service performance.

The primary alloying elements include silicon (Và), đồng (Cu), và magiê (Mg), while iron (Fe), Mangan (Mn), kẽm (Zn), and other trace elements act as controlled additives or impurities to fine-tune processability and properties.

1. Các yếu tố hợp kim chính: Defining Core Performance

Primary alloying elements are added in relatively high concentrations (typically ≥1 wt%) and are responsible for the fundamental classification and core properties of die-cast nhôm hợp kim.

Silicon, đồng, and magnesium are the most critical, as they directly govern castability, sức mạnh, and corrosion resistance—the three key criteria for alloy selection.

Silicon (Và): The Cornerstone of Castability

Silicon is the most predominant alloying element in nearly all commercial die-cast aluminum alloys, with typical concentrations ranging from 7–18 wt%.

Its primary role is to drastically improve molten fluidity and reduce solidification defects, while also contributing to strength, Độ cứng, and dimensional stability—making it indispensable for casting intricate, Các thành phần có thành mỏng.

This is particularly critical for high-pressure die casting (HPDC), where molten metal must fill micro-cavities (wall thickness ≤0.6 mm) at high velocities (2–5 m/s) without cold shuts or misruns.

Mechanisms of Action:

• Enhanced Fluidity: Si lowers the liquidus temperature of aluminum (từ 660 °C for pure Al to 570–600 °C for Al-Si alloys) and reduces the viscosity of molten metal by decreasing atomic bonding forces.
  The high heat of crystallization of Si also prolongs the molten state, extending flow length.
  Per NADCA test data, a hypoeutectic Al-Si alloy (7–9 wt% Si, VÍ DỤ., A380) achieves a spiral fluidity of 380–450 mm at 720 ° C.,
  while a near-eutectic alloy (10.7–12.5 wt% Si, VÍ DỤ., A413) reaches 450–520 mm—an improvement of 15–20%—and a hypereutectic alloy (14–16 wt% Si, VÍ DỤ., B390) reaches 480–550 mm.
• Reduced Solidification Shrinkage: Pure aluminum exhibits a volumetric shrinkage of ~6.6% during solidification, which causes shrinkage porosity and dimensional distortion.
  Si reduces this shrinkage to 4.5–5.5% by forming a eutectic (α-Al + Và) structure that solidifies uniformly.
  As Si approaches the eutectic level (11.7 wt% in the Al-Si binary system), the solidification interval (liquidus–solidus temperature difference) narrows drastically—from 40–55 °C for hypoeutectic alloys to only 15 °C for near-eutectic alloys (VÍ DỤ., A413).
  This narrow interval minimizes the time the alloy spends in the brittle semi-solid “mushy zone,”
  reducing hot tearing (hot shortness) tendency: near-eutectic alloys have a hot tearing rejection rate <0.3%, compared to 1.5–3.0% for hypoeutectic alloys with lower Si (VÍ DỤ., A356, 6.5–7.5 wt% Si).
• Strengthening and Stiffness: Si forms hard, dispersion-strengthened particles (eutectic Si or primary Si) in the soft α-Al matrix.
  Si eutectic (Độ cứng ≈ 800 HV) resists plastic deformation, while primary Si (formed in hypereutectic alloys, Độ cứng ≈ 1000 HV) significantly improves wear resistance.
  Si also increases the modulus of elasticity (từ 70 GPa for pure Al to 75–80 GPa for Al-Si alloys) and lowers the coefficient of thermal expansion (CTE),
  enhancing dimensional stability under thermal cycling—critical for components like heat sinks and precision housings.

Content Effects and Trade-Offs:

• Hypoeutectic (Si = 7–11.7 wt%): Alloys like A380 (7.5–9.5 wt% Si) and A360 (9.0–10.0 wt% Si) form primary α-Al grains plus eutectic (α-Al + Và).
  They balance strength (UTS = 260–380 MPa) và độ dẻo (elongation = 2.0–5.0%) but have lower fluidity than near-eutectic alloys.
  These are the most widely used die-cast alloys, suitable for general-purpose structural components (VÍ DỤ., vỏ ô tô, dấu ngoặc).
• Near-Eutectic (Và ≈ 11.7 wt%): Alloys like A413 (10.7–12.5 wt% Si) have minimal primary α-Al, with most of the microstructure consisting of fine eutectic.
  They exhibit the best fluidity, độ kín áp lực (leakage rejection rate <0.5%), and hot tearing resistance—making them ideal for pressure-retaining components (VÍ DỤ., đa tạp thủy lực, thân van) and ultra-thin-walled parts (0.6Hàng0,8 mm).
• siêu âm (Si = 12–18 wt%): Alloys like B390 (14–16 wt% Si) form coarse primary Si particles plus eutectic.
  Primary Si drastically improves wear resistance (suitable for engine cylinders, pistons) but reduces ductility (kéo dài <2.0%) and machinability due to the abrasive nature of primary Si particles.
  Excessively high Si (>18 wt%) causes severe brittleness and casting defects.

Tóm lại, Si is the “enabler” of die casting for aluminum, making it possible to produce intricate, defect-free components while enhancing pressure tightness and stiffness—explaining why Al-Si alloys dominate 90%+ of commercial die-cast aluminum applications (NADCA statistics).

đồng (Cu): The Primary Strength Enhancer

Copper is added to die-cast aluminum alloys in concentrations ranging from 0.1–4.0 wt%, primarily to boost mechanical strength and hardness via solid solution strengthening and precipitation hardening.

It is the key element for alloys requiring high load-bearing capacity, such as automotive structural components and heavy-duty brackets.

Per ASTM B85 standards, Cu content is tightly controlled to balance strength and other properties.

Mechanisms of Action:

• Dung dịch rắn tăng cường: Cu has a high solubility in the α-Al matrix (lên đến 5.6 wt% at 548 ° C.), distorting the face-centered cubic (FCC) lattice of aluminum.
  This distortion increases resistance to plastic deformation, significantly raising tensile strength and hardness.
  Ví dụ, A380 (Al–Si–3.5Cu) has a UTS of ~324 MPa and Brinell hardness (HB) of 80–100, compared to ~310 MPa and 75–95 HB for A360 (Al–Si–0.5Cu) and ~290 MPa and 70–90 HB for A413 (Al–Si–0.05Cu).
• Lượng mưa cứng: In heat-treatable die-cast alloys (VÍ DỤ., A201, Cu = 4.0–5.0 wt%), Cu forms fine Al₂Cu precipitates during T5/T6 heat treatment (Giải pháp ủ + Lão hóa), further increasing strength.
  Tuy nhiên, most die-cast alloys (VÍ DỤ., A380, A413) are not heat-treated industrially due to the rapid cooling during HPDC,
  which traps Cu in solid solution—nevertheless, the solid solution strengthening effect alone is sufficient for most high-strength applications.
• Cường độ nhiệt độ cao: Cu improves strength retention at elevated temperatures (150Mùi250 ° C.) by stabilizing the α-Al matrix and preventing grain growth,
  making it suitable for components exposed to moderate heat (VÍ DỤ., dấu ngoặc động cơ, exhaust system parts).

Trade-Offs and Limitations:

• Reduced Castability: Cu widens the solidification interval of Al-Si alloys—A380 has a 40 °C interval vs. 15 °C for A413—increasing hot tearing tendency and shrinkage porosity.
  Careful gating/risering design, chill application, and process parameter tuning (VÍ DỤ., lower injection speed, higher die temperature) are required to mitigate these defects.
• Severely Degraded Corrosion Resistance: Cu forms galvanic cells with aluminum (Cu acts as a cathode, Al as an anode), accelerating pitting corrosion in humid, nước mặn, or industrial environments.
  Even small Cu levels (0.3–0.5 wt%) can promote localized corrosion, while levels >1.0 wt% (VÍ DỤ., A380) make the alloy unsuitable for outdoor or marine applications without surface treatments (Anod hóa, lớp phủ bột).
  Ngược lại, alloys with low Cu (<0.15 wt%, VÍ DỤ., A413, A360) exhibit excellent corrosion resistance, with a service life 3–5 times longer than A380 in ASTM B117 salt spray tests.
• Reduced Ductility: Cu forms brittle intermetallic phases (Al₂cu, Al₅Cu₂Mg₈Si₆) tại ranh giới hạt, which act as stress risers and reduce ductility.
  A380 has an elongation of 2.0–3.0%, compared to 3.5–6.0% for A413 and 3.0–5.0% for A360.

Về bản chất, Cu is a “strength-for-corrosion” trade-off element: it enables high-strength die-cast components but requires careful consideration of corrosion risks and casting process adjustments.

Magiê (Mg): Synergistic Strength and Corrosion Control

Magnesium is added to die-cast aluminum alloys in concentrations ranging from 0.05–5.0 wt%, with its role varying dramatically based on content.

In most Al-Si die-cast alloys (VÍ DỤ., A413, A380), Mg is kept low (~0.05–0.1 wt%) to prioritize castability, while in specialized alloys (VÍ DỤ., A360, 518), it is elevated to enhance strength and corrosion resistance.

Mechanisms of Action:

• Precipitation Hardening via Mg₂Si: Mg reacts with Si in the alloy to form Mg₂Si (Độ cứng ≈ 450 HV), a highly effective strengthening phase.
  The Mg₂Si phase precipitates during solidification or heat treatment, improving yield strength and wear resistance.
  Ví dụ, A360 (0.45–0.6 wt% Mg) has a yield strength of 160–190 MPa (như đúc), compared to 140–160 MPa for unmodified A413.
  In heat-treatable alloys like A356 (0.25–0.45 wt% Mg), T6 heat treatment maximizes Mg₂Si precipitation, increasing yield strength to 310–350 MPa.
• Dung dịch rắn tăng cường (Low Mg Content): At low concentrations (0.05–0.1 wt%), Mg dissolves in the α-Al matrix, providing modest solid solution strengthening without significantly degrading fluidity.
  It also aids chip formation during machining, improving machinability by reducing built-up edge on cutting tools.
• Tăng cường kháng ăn mòn: Mg stabilizes the native Al₂O₃ passive oxide film on the alloy surface, making it denser and more adherent.
  This significantly improves corrosion resistance in atmospheric, nước ngọt, and mild saltwater environments.
  Hợp kim 518 (5–6 wt% Mg, Al-Mg system) exhibits the best corrosion resistance of any common die-cast alloy, with excellent anodizing performance and resistance to stress corrosion cracking (SCC).
• Work-Hardening Capability: Mg enhances the work-hardening rate of aluminum, allowing post-casting forming operations (VÍ DỤ., uốn cong, staking) for components requiring minor shaping.

Trade-Offs and Limitations:

• Reduced Castability at High Mg Content: Mg increases the viscosity of molten aluminum and widens the solidification interval.
  Beyond ~0.3 wt%, fluidity decreases significantly, and hot tearing tendency increases.
  Hợp kim 518 (5–6 wt% Mg) has very poor die-filling capacity, making it unsuitable for thin-walled HPDC parts and limiting its use to gravity die casting or semi-solid casting of thick-walled components (VÍ DỤ., Phụ kiện hàng hải).
• Hydrogen Sensitivity: Mg readily reacts with moisture in the melt (from raw materials, furnace tools, or mold release agents) to form Mg(Ồ)₂ and hydrogen gas, increasing porosity.
  Strict melt degassing (argon or nitrogen rotary degassing) is required for Mg-containing alloys to reduce hydrogen content to <0.15 cc/100g Al (ASTM E259).
• Oxidation Sensitivity: Mg oxidizes rapidly at high temperatures, forming a loose MgO scale that contaminates the melt and causes casting defects.
  Molten Mg-containing alloys require protective flux or inert gas (Argon) coverage to prevent oxidation.

2. Secondary Alloying Elements: Regulating Microstructure and Processability

Secondary alloying elements are added in low concentrations (0.1–1.5 wt%) and act as “microstructure modifiers” to mitigate the harmful effects of impurities (VÍ DỤ., Fe), tinh chỉnh các hạt, prevent mold sticking, and fine-tune properties.

Sắt, Mangan, and titanium are the most critical, with their roles closely interdependent.

Sắt (Fe): A “Necessary Impurity” for Mold Release

Iron is typically considered an impurity in aluminum alloys, but in die casting, it is intentionally controlled at 0.6–1.2 wt% (per NADCA recommendations) to prevent mold sticking (hàn),

a critical issue in HPDC where molten aluminum adheres to the steel mold surface, causing surface defects (VÍ DỤ., Galling) and reducing mold life.

Without Fe, molten aluminum would weld to the steel mold, making large-scale production infeasible.

Mechanisms of Action:

• Preventing Mold Sticking: Fe forms a thin, adherent Fe-Al intermetallic layer (primarily FeAl₃) at the mold-aluminum interface, acting as a barrier to adhesion.
  This layer reduces the wettability of molten aluminum on steel, preventing soldering and extending mold life by 15–20% compared to low-Fe alloys (<0.5 wt%).
• Reducing Hot Tearing: Fe depresses the eutectic temperature of Al-Si alloys slightly, narrowing the solidification interval and reducing hot tearing tendency—complementing the effect of Si.
• Improving Dimensional Stability: Controlled Fe content (0.8–1.0 wt%) reduces grain growth during solidification, enhancing dimensional stability and reducing thermal cycling distortion.

Harmful Effects and Mitigation:

• Brittle Intermetallic Formation: Fe has almost zero solubility in solid aluminum and forms hard, acicular β-Al₉Fe₂Si₂ intermetallics (Độ cứng ≈ 900 HV) in the microstructure.
  These needle-like particles act as crack initiators, drastically lowering ductility and toughness—excess Fe (>1.2 wt%) can reduce elongation by 50% or more and cause brittle fracture in service.
• Strength Reduction: Beyond ~0.5 wt%, Fe begins to reduce tensile strength by forming coarse intermetallics that disrupt the α-Al matrix.
  Ví dụ, an Al-Si alloy with 1.5 wt% Fe has a UTS 10–15% lower than the same alloy with 0.8 wt% Fe.
• Mitigation via Mn/Cr: Adding manganese (Mn) hoặc crom (Cr) modifies the acicular β-Al₉Fe₂Si₂ intermetallics into compact,
  Chinese-script shaped α-AlFeMnSi or α-AlFeCrSi intermetallics, which are less harmful to ductility and toughness.
  The optimal Mn/Fe ratio is 0.5–0.8: Mn/Fe <0.5 results in incomplete modification, while Mn/Fe >0.8 forms coarse Al₆Mn intermetallics that reduce ductility.

Mangan (Mn): Modifying Fe-Rich Intermetallics

Manganese is added to nearly all die-cast aluminum alloys in concentrations of 0.1–0.5 wt%, with its sole primary role being to neutralize the harmful effects of Fe.

Unlike Cu or Mg, Mn does not significantly alter castability or corrosion resistance, making it a “beneficial modifier” with minimal trade-offs.

Mechanisms of Action:

• Fe-Phase Modification: Mn reacts with Fe and Si in the melt to form α-AlFeMnSi intermetallics, which have a compact, non-acicular morphology (Chinese-script or globular) compared to the brittle acicular β-Al₉Fe₂Si₂.
  This modification reduces stress concentration and prevents crack propagation, improving ductility and toughness by 20–30%.
  Ví dụ, in A413 (Fe ≤1.5 wt%, Mn ≤0.5 wt%), Mn modifies β-AlFeSi to α-AlFeMnSi, increasing elongation from 1.5–2.5% (chưa sửa đổi) to 3.5–6.0% (modified).
• Modest Solid Solution Strengthening: Mn dissolves slightly in the α-Al matrix (solubility ≈ 1.8 wt% at 658 ° C.), providing modest solid solution strengthening without significant ductility loss.
  This increases tensile strength by 5–10% compared to unmodified alloys.
• Sàng lọc hạt: Mn forms fine Al₆Mn intermetallics at low concentrations, which act as heterogeneous nucleation sites for α-Al grains, refining the microstructure and improving property uniformity.

Content Control: Mn is strictly limited to ≤0.5 wt% (Hen suyễn B85) because excess Mn forms coarse Al₆Mn intermetallics, which act as stress risers and reduce ductility.

Concentrations <0.1 wt% are insufficient to fully modify Fe-rich intermetallics, leaving residual acicular β-Al₉Fe₂Si₂.

Titan (Của): Sàng lọc hạt

Titanium is added to die-cast aluminum alloys in concentrations of 0.1–0.2 wt%, primarily as a grain refiner to improve microstructure uniformity, reduce hot tearing, and enhance mechanical properties.

It is often used in combination with boron (B) for more effective refinement.

Mechanisms of Action:

• Heterogeneous Nucleation: Ti reacts with Al to form TiAl₃ particles, which have a crystal structure similar to α-Al (FCC) and act as nucleation sites for α-Al grains during solidification.
  This refines the α-Al grain size from 200–300 μm (unrefined) to 50–100 μm (Ti-refined), improving tensile strength by 10–15% and elongation by 20–30%.
• Reducing Hot Tearing: Khỏe, equiaxed grains formed by Ti refinement distribute tensile stress more uniformly during solidification,
  reducing hot tearing tendency by 40–50%—particularly beneficial for hypoeutectic alloys with wide solidification intervals (VÍ DỤ., A356).
• Improving Property Uniformity: Refined grains reduce microstructural segregation, ensuring consistent mechanical properties across the cast component—critical for precision components (VÍ DỤ., vỏ điện tử, hydraulic valves).

Synergistic Effect with Boron (B): Adding boron (0.005–0.01 wt%) with Ti forms TiB₂ particles, which are more stable and effective nucleation sites than TiAl₃.

The Al-5Ti-1B master alloy is widely used in industry, allowing for lower Ti concentrations (0.1 wt% Ti + 0.02 wt% B) to achieve the same refinement effect as 0.2 wt% Ti alone.

3. Other Trace Elements: Fine-Tuning Properties and Processability

Trace elements (added in concentrations ≤0.5 wt%) are used to fine-tune specific properties or processability, with each element serving a niche role.

Niken (TRONG), crom (Cr), strontium (Sr), chỉ huy (PB), và bismuth (Bi) are the most common.

Niken (TRONG) and Chromium (Cr): Độ ổn định nhiệt độ cao

• Niken (TRONG, ≤0.5 wt%): Ni improves high-temperature hardness, Khả năng chống creep, and wear resistance by forming hard intermetallic phases (Al₃Ni, AlNiSi).
  It also reduces the CTE, enhancing dimensional stability at elevated temperatures (200Mùi300 ° C.).
  Alloys like B390 (14–16 wt% Si + 0.5 wt% Ni) are used for high-heat, wear-resistant components (VÍ DỤ., engine cylinders, piston sleeves).
  Tuy nhiên, Ni increases density slightly and reduces ductility, so it is only added when high-temperature performance is critical.
• Crom (Cr, 0.1–0.5 wt%): Cr controls grain growth at elevated temperatures, improving high-temperature strength retention.
  It also modifies Fe-rich intermetallics similarly to Mn, giảm độ giòn. Cr is often used in combination with Ni for synergistic high-temperature performance.

Strontium (Sr): Eutectic Si Modification

Sr is added in trace concentrations (0.015–0,03% khối lượng) to modify the morphology of eutectic Si in Al-Si alloys.

In unmodified alloys, eutectic Si grows as coarse, acicular particles that reduce ductility—Sr converts these into fine, fibrous particles, doubling elongation (VÍ DỤ., from 1.5–2.5% to 3.5–6.0% for A413).

Sr is the industrial standard modifier for HPDC due to its long persistence (lên đến 60 phút) and compatibility with rapid casting cycles.

Tuy nhiên, it is poisoned by phosphorus (P >0.001 wt%), which forms AlP particles that negate Si modification—strict P control is required for effective Sr modification.

Chỉ huy (PB) and Bismuth (Bi): Gia công miễn phí

Pb and Bi are added in concentrations of 0.1–0.3 wt% to improve machinability by forming low-melting-point phases (PB: 327 ° C., Bi: 271 ° C.) tại ranh giới hạt.

These phases act as “chip breakers,” reducing cutting forces and tool wear.

Tuy nhiên, they make the alloy non-weldable and reduce ductility, so they are only used in components requiring high machinability (VÍ DỤ., ốc vít, Bánh răng chính xác).

4. Combined Effects on Castability and Mechanical Performance

The performance of a die-cast aluminum alloy is not determined by individual elements alone, but by their synergistic and antagonistic interactions.

The goal of alloy design is to balance castability (lưu động, hot tearing resistance) và hiệu suất cơ học (sức mạnh, độ dẻo, độ cứng) based on application requirements.

Key element interactions and their practical consequences

Silicon × Magnesium (Si–Mg)

• Metallurgical interaction: Mg combines with Si to form Mg₂Si precipitates after solution heat treatment and aging.
  The presence of Si also controls how much Mg remains in solid solution versus partitioned into intermetallics during solidification.
• Castability effect: Near-eutectic Si improves fluidity and reduces the freezing range, facilitating thin-wall filling.
  Increasing Mg beyond modest levels tends to reduce fluidity and widen the effective freezing interval, increasing hot-tear risk.
• Mechanical trade-off: Và + Mg enables heat-treatable strengths (via Mg₂Si) while retaining reasonable stiffness and thermal stability.
  The best compromise is a near-eutectic Si with controlled Mg to allow both castability and post-cast strengthening.

Silicon × Copper (Si–Cu)

• Metallurgical interaction: Cu precipitates (Al–Cu phases) form during aging and increase strength but act independently of Si-rich eutectic structures.
• Castability effect: Cu does not significantly improve fluidity; excessive Cu can increase the tendency for hot-shortness and intergranular cracking if the solidification path becomes complex.
• Mechanical trade-off: Cu offers strong increases in UTS and high-temperature retention, but at the penalty of corrosion susceptibility and sometimes reduced ductility when combined with coarse eutectic structures.

Copper × Magnesium (Cu–Mg)

• Metallurgical interaction: Both contribute to age-hardening in some Al–Si–Cu–Mg alloys through separate precipitate chemistries; interactions between precipitate populations can affect over-age behavior.
• Performance effect: Combining modest Cu and Mg gives a wider tuning range for strength and toughness but raises demands on heat-treatment control and can accentuate microgalvanic corrosion if surface finish is poor.

Iron × Manganese / Crom (Fe–Mn/Cr)

• Metallurgical interaction: Fe forms hard Al–Fe–Si intermetallics that are brittle.
  Mn and Cr convert acicular/needle β-phases into more compact, “Chinese-script” or globular morphologies that are far less detrimental.
• Castability and mechanical effect: Controlled Fe with Mn/Cr modification reduces cracking initiation at intermetallics, improving toughness and fatigue life with negligible negative impact on fluidity.
  This is a classic ‘damage control’ strategy when scrap or process constraints introduce unavoidable Fe.

Hypereutectic Si, Nickel and Wear/High-Temperature Additives

• Metallurgical interaction: High Si content produces primary Si particles. Ni and some Mo/Cr additions stabilize intermetallic networks at elevated temperature.
• sự đánh đổi: These combinations yield excellent wear and thermal stability but dramatically reduce ductility and complicate machining and die filling. Use only when wear resistance or thermal creep strength is dominating.

Zinc interactions

• Metallurgical interaction: Zn in small amounts can raise strength slightly; at higher levels it broadens the solidification range and increases hot-tear susceptibility.
• Lưu ý thực tế: Zn is typically constrained to low levels in die-cast Al to avoid castability problems.

Typical Alloy Performance Comparisons (HPDC, Như đúc):

5. Corrosion Resistance and Thermal Stability

Alloy composition is a primary determinant of corrosion resistance and high-temperature performance—two critical properties for components exposed to harsh environments or prolonged heat.

Key elements exert distinct, often opposing effects on these performance metrics, requiring careful balancing during alloy design.

Kháng ăn mòn

• Cu is Detrimental: Cu is the primary element reducing corrosion resistance, as it forms galvanic cells with Al.
  Alloys with Cu >1.0 wt% (VÍ DỤ., A380) require surface treatments to avoid pitting corrosion.
  Low-Cu alloys (<0.15 wt%, VÍ DỤ., A413, A360) exhibit excellent corrosion resistance, making them suitable for outdoor applications.
• Mg is Beneficial: Mg stabilizes the Al₂O₃ passive film, cải thiện khả năng chống ăn mòn.
  Hợp kim 518 (high Mg) is the most corrosion-resistant common die-cast alloy, suitable for marine and outdoor applications where exposure to moisture or saltwater is inevitable.
• Si is Neutral-to-Beneficial: Si up to ~12 wt% improves corrosion resistance by forming a more stable oxide film. Hypereutectic Si (>12 wt%) may reduce corrosion resistance slightly due to coarse primary Si particles, which act as corrosion sites.
• Mn is Neutral: Mn has little direct impact on corrosion but improves uniformity, reducing localized corrosion spots that can lead to premature failure.

ASTM B117 salt spray tests confirm these trends: A413 shows no significant pitting after 1000 giờ, while A380 exhibits severe pitting after 200 hours—highlighting the critical role of Cu content in corrosion performance.

Ổn định nhiệt

• Cường độ nhiệt độ cao: Cu and Ni improve strength retention at 150–300 °C.
  Ni-containing alloys (VÍ DỤ., B390) are used for high-heat components, as they maintain hardness and strength even under prolonged exposure to elevated temperatures.
  Cr also aids in high-temperature strength retention by controlling grain growth.
• Sự ổn định kích thước: Si and Ni/Cr reduce the CTE, enhancing dimensional stability under thermal cycling.
  High-Si alloys (VÍ DỤ., A413, B390) have a CTE of 21.0–22.5 × 10⁻⁶ /°C, compared to 22.0–23.5 × 10⁻⁶ /°C for low-Si alloys (VÍ DỤ., 518)—making them ideal for precision components that must maintain shape under temperature fluctuations.
• Khả năng chống creep: Ni and Cr improve creep resistance (deformation under long-term stress at elevated temperatures), critical for engine components and hydraulic valves that operate under constant load and heat.

6. Hệ thống hợp kim: Al-si, Al-mg, and Beyond

Commercial die-cast aluminum alloys fall into three primary systems, with the Al-Si system dominating due to its balanced castability and performance.

Each system is tailored to specific application needs, with alloy composition optimized to address key performance requirements.

Al-Si System (300 Và 400 Loạt)

This system accounts for over 90% of die-cast aluminum applications, with alloys containing 6–18 wt% Si and varying Cu/Mg concentrations.

Key subcategories are defined by their Si content relative to the eutectic point (11.7 wt%):

• Hypoeutectic (300 Loạt): A380, A360, A383, A384 (Si=7–11.7 wt%).
  These alloys balance castability and strength, suitable for general-purpose structural components (VÍ DỤ., vỏ ô tô, dấu ngoặc) where both processability and performance are required.
• Near-Eutectic (400 Loạt): A413 (Si=10.7–12.5 wt%).
  These alloys exhibit the best fluidity and pressure tightness, ideal for thin-walled, leak-critical components (VÍ DỤ., đa tạp thủy lực, thân van).
• siêu âm (B Series): B390 (Si=14–16 wt%).
  These alloys offer high wear resistance due to coarse primary Si particles, suitable for engine cylinders and pistons where wear is a primary concern.

Al-Mg System

Represented primarily by alloy 518 (Al–5%Mg), this system lacks significant Si or Cu.

It exhibits the best corrosion resistance and ductility of any common die-cast alloy but has very poor castability (tính lưu động thấp, high hot tearing tendency).

Kết quả là, it is limited to gravity die casting or semi-solid casting of thick-walled, corrosion-sensitive components (VÍ DỤ., Phụ kiện hàng hải, các bộ phận kiến ​​trúc) where corrosion resistance is prioritized over castability.

Al-Zn System

There are no widely used die-cast alloys in this system, as Zn-dominant alloys (7Sê -ri XXX) are typically wrought (not die-cast).

Zn appears only as a minor additive (0.5–3.0 wt%) in die-cast alloys (VÍ DỤ., ADC12/A383) to improve machinability and moderate strength, but high Zn promotes hot cracking and reduces corrosion resistance—limiting its use to niche applications.

7. Effects on Different Die-Casting Processes

Alloy selection is closely tied to the die-casting process, as each process has distinct requirements for fluidity, Tốc độ hóa rắn, and melt reactivity.

Matching the alloy to the process ensures optimal casting quality and component performance.

Đúc chết áp suất cao (HPDC)

HPDC requires rapid mold filling (2–5 m/s) of thin sections (≤1.0 mm), favoring high-Si alloys with excellent fluidity and narrow solidification intervals.

Key alloys include A380, A383, A384 (hypoeutectic Si) and A413 (near-eutectic Si).

These alloys fill intricate dies quickly and have low hot tearing tendency, making them suitable for high-volume production of complex components.

Low-Cu alloys (A360, A413) are used when mold sticking is a concern, while Mg-rich alloys (518) are generally unsuitable for HPDC due to poor fluidity.

Low-Pressure and Gravity Die Casting

These processes allow slower filling (0.1–0.5 m/s) and thicker sections (31010 mm), permitting the use of alloys with lower fluidity but better service properties.

Alloys like A360 (balanced strength/corrosion) Và 518 (excellent corrosion/ductility) are used here, as slower filling reduces turbulence and porosity—improving component quality.

The gentler solidification also minimizes hot tearing in Mg-rich alloys, expanding their applicability.

Semi-Solid Die đúc

This process uses a semi-solid slurry (50–60% solid) to fill molds, favoring alloys with fine microstructures (VÍ DỤ., A356, A360) that can be easily thixocast.

Grain refiners (Ti/B) are often used to improve slurry uniformity, while Mg and Cu are controlled to balance strength and processability—making this process suitable for high-precision, Các thành phần cường độ cao.

8. Kết luận

Alloying elements are the foundation of die-cast aluminum alloy performance, governing microstructure evolution, casting processability, and service properties.

Their roles are defined by clear metallurgical mechanisms and interdependencies: Si enables castability and pressure tightness, Cu enhances strength at the cost of corrosion resistance, Mg balances strength and corrosion resistance, Fe prevents mold sticking (with Mn mitigation), and trace elements fine-tune specific properties.

The key to successful alloy selection and design is balancing the synergistic and antagonistic effects of these elements to meet the specific requirements of the application and casting process.

For intricate, pressure-tight components, near-eutectic Al-Si alloys (VÍ DỤ., A413) are ideal; for high-strength structural parts, hypoeutectic Al-Si-Cu alloys (VÍ DỤ., A380) được ưa thích; for corrosion-sensitive components, low-Cu Al-Si-Mg or Al-Mg alloys (VÍ DỤ., A360, 518) are chosen.

As lightweight manufacturing, Xe điện, and precision die casting advance, alloying element design will continue to evolve—with a focus on low-Cu, low-impurity, and rare earth-modified alloys that offer improved sustainability, kháng ăn mòn, và hiệu suất nhiệt độ cao.