Thermal conductivity against densityHigher and further left: spreads more heat for its weightThermal expansion against thermal conductivityLower and further right: warps less when heated
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Sources4 documents: Magnesium Elektron, Isola, Park Electrochemical (Nelco), U.S. Department of Defense
Magnesium AZ91D
ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.
PCB Laminate FR-4
Isola 370HR FR-4 laminate (Polyclad PCL-FR-370HR, 180 C Tg multifunctional epoxy, E-glass fabric), copper removed; Isola data sheet Revision C, last updated April 15, 2021. Woven-glass laminate: the sheet gives in-plane values per weave direction (length / cross) and the Z-axis CTE separately; the solver is isotropic per material.
1
Elektron Die Casting Alloys (Datasheet 475)Magnesium Elektronarchived copyMagnesium AZ91D · Yield strength: typical, 0.2% tensile yield, ambient temperatureMagnesium AZ91D · Ultimate tensile strength: typical, ambient temperatureMagnesium AZ91D · Elongation at break: typical, ambient temperatureMagnesium AZ91D · Young's modulus (stiffness): typicalMagnesium AZ91D · Density: typicalMagnesium AZ91D · Thermal conductivity: typicalMagnesium AZ91D · Thermal expansion: typical, temperature range not statedMagnesium AZ91D · Specific heat: typicalMagnesium AZ91D · Melting point: melting range
2
370HR Laminate and Prepreg Data SheetIsolaarchived copyPCB Laminate FR-4 · Ultimate tensile strength: typical, in-plane: cross direction .. length direction (ASTM D3039)PCB Laminate FR-4 · Flexural strength: typical: cross direction .. length direction (IPC-TM-650 2.4.4B)PCB Laminate FR-4 · Young's modulus (stiffness): typical, in-plane: cross direction .. length direction (ASTM D790-15e2)PCB Laminate FR-4 · Poisson's ratio: typical, in-plane: cross direction .. length directionPCB Laminate FR-4 · Thermal conductivity: typical (ASTM E1952); direction not stated by the sheetPCB Laminate FR-4 · Thermal expansion: typical, in-plane X/Y-axis, below Tg (IPC-TM-650 2.4.24C)PCB Laminate FR-4 · Glass transition: typical, DSC (IPC-TM-650 2.4.25C)PCB Laminate FR-4 · Max service temperature: UL Relative Thermal Index (UL 796)
3
N4000-6 Laminate Data Sheet (2006)Park Electrochemical (Nelco)archived copyPCB Laminate FR-4 · Density: typical, 50% resin content; another FR-4 producer: Park Nelco N4000-6 (high-Tg multifunctional epoxy), not Isola 370HRPCB Laminate FR-4 · Specific heat: typical (ASTM E1461); another FR-4 producer: Park Nelco N4000-6 (high-Tg multifunctional epoxy), not Isola 370HR
4
MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseMagnesium AZ91D · Poisson's ratio: base material: AZ91C casting (MIL-HDBK-5J handbook physical constant)
Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Mechanical
Is Magnesium AZ91D stronger than PCB Laminate FR-4?
PCB Laminate FR-4 is stronger: its tensile strength is 315 MPa against yield strength 150 MPa for Magnesium AZ91D (2.1x).
Which is lighter, Magnesium AZ91D or PCB Laminate FR-4?
Magnesium AZ91D is lighter: 1,810 kg/m³ against 1,920 kg/m³ for PCB Laminate FR-4.
Which is stiffer, Magnesium AZ91D or PCB Laminate FR-4?
Magnesium AZ91D is stiffer: Young's modulus 45 GPa against 23.9 GPa for PCB Laminate FR-4, so the same part in Magnesium AZ91D deflects less under the same load.
Which is lighter for the same job, Magnesium AZ91D or PCB Laminate FR-4?
For the same stiffness or strength: Magnesium AZ91D is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate; PCB Laminate FR-4 is lighter for a strong rod or tie, strong beam, strong panel or plate.
Part that must be
Magnesium AZ91D
PCB Laminate FR-4
Stiff rod or tie (tension)
lighter
2x heavier
Stiff beam (bending)
lighter
46% heavier
Stiff panel or plate
lighter
31% heavier
Strong rod or tie
1.98x heavier
lighter
Strong beam
1.55x heavier
lighter
Strong panel or plate
37% heavier
lighter
For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).
Thermal
Which conducts heat better, Magnesium AZ91D or PCB Laminate FR-4?
Magnesium AZ91D conducts heat better: 72 W/m·K against 0.4 W/m·K for PCB Laminate FR-4.
Which expands less with temperature?
PCB Laminate FR-4 expands less: 13.5 µm/m·K against 25 µm/m·K for Magnesium AZ91D.