Fractography Resource - [email protected] 1 Examples of Aluminium Fractography Professor M Neil James [email protected] Department of Mechanical

Fractography Resource - [email protected]

Examples of Aluminium Fractography

Professor M Neil [email protected]

Department of Mechanical & Marine Engineering

University of Plymouth

Drake Circus, Plymouth PL4 8AA

ENGLAND

mailto:[email protected]


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



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



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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Al 0.8-1.0Mg 0.4-0.8Si 0.70Fe 0.15-0.40Cu 0.25Zn 0.15Ti 0.15Mn

Peak aged - PS = 312 MPa – extruded rod

Crack initiation region

Original magnification given by micron marker





Crack initiation region – smooth areas of slip band cracking are present






Crack growth appears to have a component of MVC


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Ductile fracture of 6061-T6 alloy



Precipitate particles are present at the bottom of voids


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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




Al 2.37Li 1.19Cu 0.82Mg 0.11Zr



IG regions are often present




Al 2.37Li 1.19Cu 0.82Mg 0.11Zr



Typical IG region at high magnification




Al 2.37Li 1.19Cu 0.82Mg 0.11Zr



'Blocky' striated fatigue also occurs




Al 2.37Li 1.19Cu 0.82Mg 0.11Zr



Regions of 'normal' striated fatigue also occur




Al 2.37Li 1.19Cu 0.82Mg 0.11Zr


Interface between ductile fast fracture (MVC) and fatigue is shown here


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Ductile fracture of 8090-T8511 Al-Li alloy

Al 2.37Li 1.19Cu 0.82Mg 0.11Zr


Typical MVC is shown here


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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






High cycle fatigue shows signs of the underlying microstructure






Low cycle fatigue appears more generally ductile striated growth






Low cycle fatigue shows clear striations at high magnification






SP FSW can lead to partial-fusion defects in the weld nugget (also called 'kissing' bonds)


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Ductile Fracture of 5383-H321 alloy



MVC in this alloy


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Defects in welded Al-Si-Mg casting alloy

Intergranular-interdendritic hot cracking

Magnification given by micron marker

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Wormhole porosity


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Possible layer porosity


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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).


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Fatigue crack (F) which has been initiated by a region of hot cracking and undercut/slag inclusion (HC+UC).


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HC+UC

F



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.


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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.


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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.


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Fractography Resource - [email protected] 1 Examples of Aluminium Fractography Professor M Neil James [email protected] Department of Mechanical