AlSi7Mg Aluminium Alloy
metalhypoeutectic Al-Si-Mg precipitation-hardenable aluminium alloy
AlSi7Mg0.6EN AC-42100EN 1706 AC-AlSi7MgA357.0 (near-equivalent)UNS A13570AlSi7Mg 0.6EOS Aluminium AlSi7Mg
Composition — EN AC-42100 / EN 1706 (near A357.0)
| Element | Min % | Max % | Notes |
|---|---|---|---|
| Al | bal. | balance | |
| Si | 6.50 | 7.500 | Primary eutectic-forming element. Lower Si than AlSi10Mg → finer, less-continuous eutectic network → better ductility |
| Mg | 0.45 | 0.700 | Forms Mg₂Si precipitates during T6 aging — primary strengthening mechanism |
| Fe | — | 0.200 | Iron limit critical in AM: Fe-rich β-needles (Al₅FeSi) are crack initiation sites. AM powder spec typically ≤0.15% Fe |
| Mn | — | 0.100 | Mn partially offsets Fe-needle embrittlement by converting β-Al₅FeSi to α-Al₁₅(Fe,Mn)₃Si₂ script phase |
| Cu | — | 0.200 | Low Cu limit to preserve corrosion resistance and anodising quality |
| Zn | — | 0.100 | |
| Ti | — | 0.150 | Grain refiner; AM powder typically 0.05–0.10% Ti for columnar-to-equiaxed transition control |
| Ni | — | 0.050 | |
| Pb | — | 0.050 | |
| Sn | — | 0.050 |
Mechanical & thermal properties — 3 conditions
| Property | LPBF + As-built (XY) | LPBF + T6 (XY) | LPBF + As-built (Z — build direction) |
|---|---|---|---|
| Elastic modulus | 71 GPa | 71 GPa | — |
| Yield strength (0.2%) | 190–235 MPa | 245–290 MPa | 175–215 MPa |
| Ultimate tensile strength | 300–350 MPa | 315–375 MPa | 275–330 MPa |
| Elongation at break | 6.0–11.0 % | 8.0–14.0 % | 5.0–9.0 % |
| Hardness (HV) | 85–110 HV10 | 95–120 HV10 | — |
| Density | 2.67 g/cm³ | 2.67 g/cm³ | — |
| Thermal conductivity | 145.0–170.0 W/m·K | 160.0–180.0 W/m·K | — |
| CTE | 21.5–23.5 µm/m·K | — | — |
Values shown as min–max where a spread is reported, otherwise as typical ± unit. Ranges reflect inter-source variation, not single-sample scatter. All values are for AM-processed specimens unless noted.
Engineering considerations
- T6 cycle optimisation: standard T6 for LPBF AlSi7Mg is 530°C/5h/WQ + 160°C/6h. Over-aging (>175°C or >8h) precipitates coarse Mg₂Si and reduces yield strength below 230 MPa. Under-aging leaves unsatisfactory Mg₂Si distribution and poor fatigue life.
- Stress relief before T6: add a stress relief step (300°C/2h/air cool) before solution treatment for large or complex parts. Reduces distortion during solution treatment quench by releasing as-built residual stresses.
- Quench rate sensitivity: water quench is standard for solution treatment. Use polymer quench (PAG solution) for complex parts with thin features — reduces quench distortion while maintaining near-water cooling rate for adequate Mg₂Si dissolution.
- Support design: AlSi7Mg supports detach more easily than steel but still require adequate cross-section. Prefer 45° angle grid supports over solid walls. Minimum support contact width: 0.4 mm for reliable detachment without substrate damage.
- Powder reuse: AlSi7Mg powder can tolerate 20–30 build cycles with regular sieving and oxygen monitoring. Si partitioning and Mg burn-off occur preferentially in the melt pool — blend at ≥30% virgin powder per cycle. Maximum O content: 0.08%.
- Anisotropy management: Z-direction properties are ~7–10% lower as-built. T6 heat treatment substantially reduces anisotropy — T6 Z/XY YS ratio typically improves to 0.95 from 0.93 as-built. For fatigue-critical applications, orient load axis in XY plane and/or HIP + T6.
- HIP considerations: HIP (520°C / 100 MPa / 4h) before T6 eliminates internal porosity and substantially improves fatigue performance (+30–60% endurance limit). Specify HIP + T6 for fatigue-critical components (rotating, cyclic loading).
- Corrosion: AlSi7Mg offers good general corrosion resistance. Anodise (hard anodise for wear resistance, class 2 for corrosion) after T6 and finish machining. Avoid crevices and dissimilar metal contacts (galvanic risk vs steel fasteners — use titanium or Al rivets).
Advantages
- Superior T6 ductility vs AlSi10Mg (11–14% vs 7–8% El) — preferred for damage-tolerant aerospace applications
- T6 yield strength comparable to wrought A357-T6 (~265 MPa) with complex LPBF geometry
- Lower Si content improves weld and repair compatibility after LPBF
- Excellent specific strength: YS/density ~99 MPa·cm³/g in T6 condition
- Good thermal conductivity (155–170 W/m·K) for heat-exchanging structures
- Low density (2.67 g/cm³) — second lightest commercially used AM metal after magnesium alloys
- Anodising quality better than AlSi10Mg (less Si exposure at surface)
Limitations
- No dedicated AM product standard (unlike Ti-6Al-4V ASTM F2924 or IN718 ASTM F3056) — qualification requires test-based approach
- T6 solution treatment at 530°C requires controlled atmosphere or vacuum furnace — rapid heating and quench critical to dissolve eutectic Si
- As-built strength lower than AlSi10Mg — if no T6 is planned, AlSi10Mg is a better as-built choice
- Hot cracking susceptibility higher than some AM aluminium alloys (AlSi12, Al-alloys with Sc) — scan strategy and preheating critical
- Not weldable with standard MIG/TIG filler without additional filler alloy selection — specify ER4043 or ER4047 filler
- Limited commercial powder sources vs AlSi10Mg — fewer second-source options for powder qualification
- LPBF support structures in AlSi7Mg are fragile due to brittle, Si-rich HAZ — design for easier support removal
Typical applications
Aerospace structural brackets, seat rails, and interior fittings requiring >8% elongationAutomotive suspension components and lightweight structural nodesThin-walled heat exchangers and thermal management structuresRacing/motorsport uprights and corner componentsUnmanned aerial vehicle (UAV) airframes and structural ribsSatellite and spacecraft brackets requiring high specific strengthIndustrial fixtures requiring weld/repair capability after LPBF
Industries
aerospaceautomotivemotorsportdefenceindustrial
Standards & certifications
Compatible AM processes (1)
Other metal materials
Ti-6Al-4V Grade 5titanium alloy — alpha-beta316L Stainless Steelaustenitic stainless steel17-4PH Stainless Steelmartensitic precipitation-hardening stainless steelAlSi10Mgaluminium-silicon alloy (cast grade adapted for AM)Inconel 718nickel superalloy — precipitation-hardenedInconel 625nickel superalloy — solid-solution-strengthenedCoCrMocobalt-chromium alloy (biomedical and aerospace grade)Maraging Steel MS1 (18Ni-300)maraging steel (ultra-high-strength, precipitation-hardened)H13 Tool Steelchromium-molybdenum hot-work tool steel
Related calculators
HT AdvisorStandard stress-relief, solution, and aging cycles for AM metals (Ti-6Al-4V, IN718, 17-4PH, AlSi10Mg, 316L, CuCrZr) per AMS, ASTM F3301, and AMS 5664.DistortionEstimate residual stress and distortion risk index (σ/σ_y) for LPBF and DED builds. Mercelis-Kruth model with preheat sensitivity table.VEDCompute LPBF VED from power, scan speed, hatch, and layer thickness. Includes process windows for common alloys.Melt PoolLPBF / DED melt pool depth, width, and cooling rate from the Rosenthal moving heat source solution. Absorptivity, thermal diffusivity, and solidification velocity.
Last reviewed: 2026-05-05 · v1 · Sources: eos-alsi7mg-2023, slm-alsi7mg-2022, aboulkhair-2019-aluminium