1. Examples of Aluminium Fractography
Professor M Neil James
Department of Mechanical & Marine Engineering
University of Plymouth
Drake Circus, Plymouth PL4 8AA
ENGLAND
Fractography Resource -

2. Contents – Use the hyperlinks to navigate around this resource
Bend fatigue of 6261-T6 alloy
Torsion fatigue of 6061-T6 alloy
Ductile fracture of 6061-T6 alloy
Fatigue of 8090-T8511 Al-Li alloy
Ductile fracture of 8090-T8511 Al-Li alloy
Bend fatigue of friction stir welded 5383-H321 alloy
Ductile fracture of 5383-H321 alloy
Defects in an aluminium-silicon-magnesium casting alloy
Fractography Resource -

3. Bend fatigue of 6261-T6 alloy
Al 0.74Mg 0.63Si 0.19Fe 0.26Cu 0.025Zn 0.020Ti
Peak aged - PS = 282 MPa – Parent Plate (I-beam flange)
Linear growth rate regime ~ 10-4 mm/cycle
Arrows indicate grain boundaries
Original magnification 80x
Fractography Resource -

4. Bend fatigue of 6261-T6 alloy
Al 0.74Mg 0.63Si 0.19Fe 0.26Cu 0.025Zn 0.020Ti
Peak aged - PS = 282 MPa – Crack at weld toe of cover plate
Linear growth rate regime ~ 10-4 mm/cycle
The HAZ appears to be embrittled, and cleavage facets are present
Original magnification 20x
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5. Torsion fatigue of 6061-T6 alloy
Al Mg Si 0.70Fe Cu 0.25Zn 0.15Ti 0.15Mn
Peak aged - PS = 312 MPa – extruded rod
Crack initiation region
Original magnification given by micron marker
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6. Torsion fatigue of 6061-T6 alloy
Al Mg Si 0.70Fe Cu 0.25Zn 0.15Ti 0.15Mn
Peak aged - PS = 312 MPa – extruded rod
Crack initiation region – smooth areas of slip band cracking are present
Original magnification given by micron marker
Fractography Resource -

7. Torsion fatigue of 6061-T6 alloy
Al Mg Si 0.70Fe Cu 0.25Zn 0.15Ti 0.15Mn
Peak aged - PS = 312 MPa – extruded rod
Crack growth appears to have a component of MVC
Original magnification given by micron marker
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8. Ductile fracture of 6061-T6 alloy
Al Mg Si 0.70Fe Cu 0.25Zn 0.15Ti 0.15Mn
Peak aged - PS = 312 MPa – extruded rod
Precipitate particles are present at the bottom of voids
Original magnification given by micron marker
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9. Fatigue of 8090-T8511 Al-Li alloy
Al 2.37Li 1.19Cu 0.82Mg 0.11Zr
Peak aged - PS = 300 MPa – large extrusion 120 mm by 100 mm
Heat treatment leads to grain boundary precipitation of Al2CuMg, which affects crack growth
IG regions are often present
Original magnification given by micron marker
Fractography Resource -

10. Fatigue of 8090-T8511 Al-Li alloy
Al 2.37Li 1.19Cu 0.82Mg 0.11Zr
Peak aged - PS = 300 MPa – large extrusion 120 mm by 100 mm
Heat treatment leads to grain boundary precipitation of Al2CuMg, which affects crack growth
IG regions are often present
Original magnification given by micron marker
Fractography Resource -

11. Fatigue of 8090-T8511 Al-Li alloy
Al 2.37Li 1.19Cu 0.82Mg 0.11Zr
Peak aged - PS = 300 MPa – large extrusion 120 mm by 100 mm
Heat treatment leads to grain boundary precipitation of Al2CuMg, which affects crack growth
Typical IG region at high magnification
Original magnification given by micron marker
Fractography Resource -

12. Fatigue of 8090-T8511 Al-Li alloy
Al 2.37Li 1.19Cu 0.82Mg 0.11Zr
Peak aged - PS = 300 MPa – large extrusion 120 mm by 100 mm
Heat treatment leads to grain boundary precipitation of Al2CuMg, which affects crack growth
'Blocky' striated fatigue also occurs
Original magnification given by micron marker
Fractography Resource -

13. Fatigue of 8090-T8511 Al-Li alloy
Al 2.37Li 1.19Cu 0.82Mg 0.11Zr
Peak aged - PS = 300 MPa – large extrusion 120 mm by 100 mm
Heat treatment leads to grain boundary precipitation of Al2CuMg, which affects crack growth
Regions of 'normal' striated fatigue also occur
Original magnification given by micron marker
Fractography Resource -

14. Fatigue of 8090-T8511 Al-Li alloy
Al 2.37Li 1.19Cu 0.82Mg 0.11Zr
Peak aged - PS = 300 MPa – large extrusion 120 mm by 100 mm
Interface between ductile fast fracture (MVC) and fatigue is shown here
Original magnification given by micron marker
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15. Ductile fracture of 8090-T8511 Al-Li alloy
Al 2.37Li 1.19Cu 0.82Mg 0.11Zr
Peak aged - PS = 300 MPa – large extrusion 120 mm by 100 mm
Typical MVC is shown here
Original magnification given by micron marker
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16. Bend Fatigue of 5383-H321 alloy
Al 4.43Mg 0.78Mn 0.12Si 0.21Zn 0.09Fe 0.09Cu 0.09Cr
Strain hardened – quarter hard - PS = 272 MPa – single pass friction stir welded
Crack initiation is from tool travel marks
Original magnification given by micron marker
Fractography Resource -

17. Bend Fatigue of 5383-H321 alloy
Al 4.43Mg 0.78Mn 0.12Si 0.21Zn 0.09Fe 0.09Cu 0.09Cr
Strain hardened – quarter hard - PS = 272 MPa – single pass friction stir welded
High cycle fatigue shows signs of the underlying microstructure
Original magnification given by micron marker
Fractography Resource -

18. Bend Fatigue of 5383-H321 alloy
Al 4.43Mg 0.78Mn 0.12Si 0.21Zn 0.09Fe 0.09Cu 0.09Cr
Strain hardened – quarter hard - PS = 272 MPa – single pass friction stir welded
Low cycle fatigue appears more generally ductile striated growth
Original magnification given by micron marker
Fractography Resource -

19. Bend Fatigue of 5383-H321 alloy
Al 4.43Mg 0.78Mn 0.12Si 0.21Zn 0.09Fe 0.09Cu 0.09Cr
Strain hardened – quarter hard - PS = 272 MPa – single pass friction stir welded
Low cycle fatigue shows clear striations at high magnification
Original magnification given by micron marker
Fractography Resource -

20. Bend Fatigue of 5383-H321 alloy
Al 4.43Mg 0.78Mn 0.12Si 0.21Zn 0.09Fe 0.09Cu 0.09Cr
Strain hardened – quarter hard - PS = 272 MPa – single pass friction stir welded
SP FSW can lead to partial-fusion defects in the weld nugget (also called 'kissing' bonds)
Original magnification given by micron marker
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21. Ductile Fracture of 5383-H321 alloy
Al 4.43Mg 0.78Mn 0.12Si 0.21Zn 0.09Fe 0.09Cu 0.09Cr
Strain hardened – quarter hard - PS = 272 MPa – single pass friction stir welded
MVC in this alloy
Original magnification given by micron marker
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22. Defects in welded Al-Si-Mg casting alloy
Intergranular-interdendritic hot cracking
Magnification given by micron marker
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23. Defects in welded Al-Si-Mg casting alloy
Wormhole porosity
Magnification given by micron marker
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24. Defects in welded Al-Si-Mg casting alloy
Possible layer porosity
Magnification given by micron marker
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25. Defects in welded Al-Si-Mg casting alloy
Illustration of the formation of layer porosity during solidification of an aluminium alloy where the freezing range is large and/or the temperature gradient is low (i.e. solidification occurs over an extended time).
Magnification given by micron marker
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26. Defects in welded Al-Si-Mg casting alloy
HC+UC
Fatigue crack (F) which has been initiated by a region of hot cracking and undercut/slag inclusion (HC+UC).
Magnification given by micron marker
Back to Contents F
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27. Defects in welded Al-Si-Mg casting alloy
Increasing the size of the image reveals faint striation-like markings whose spacing indicate a fast growth rate of ~ 1x10-3 mm/cycle of load at this point.
Magnification given by micron marker
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28. Defects in welded Al-Si-Mg casting alloy
Illustrative crack growth rate curve for an Al alloy; a crack growth rate of 1x10-3 mm/cycle of load lies in Region III of the curve.
Magnification given by micron marker
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29. Defects in welded Al-Si-Mg casting alloy
Parts of both the fatigue and the brittle fracture surfaces, as well as some regions of porosity show the presence of needles, which EDS indicated are likely to be the iron-rich β-phase, Al5FeSi.
This phase is known to detrimentally influence the mechanical properties of Al-Si-Mg alloys.
Magnification given by micron marker
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