Effect of microstructure on fatigue life and fracture morphology in an aluminum alloy

De, Partha Sarathi; Mishra, Rajiv S.; Smith, C.

doi:10.1016/j.scriptamat.2008.11.032

Cited by 78 publications

(30 citation statements)

References 8 publications

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“…[17][18][19][20][21][22][23][24][25][26] While the FSW of aluminum alloys has engendered considerable scientific and technological interest, material property data are still limited, especially on fatigue properties that directly limit the widespread applications of the FSW process. [7,[18][19][20][21][22][23][24][25][26] The 7xxx-series aluminum alloys exhibit very high strength but also poor ductility and high notch sensitivity. [27] The fatigue of the commercial 7075Al-T6 alloy has received considerable attention.…”

Section: Introductionmentioning

confidence: 99%

“…[22] From an engineering design perspective, the fatigue properties of the friction-stir-welded aluminum alloys are of particular importance. This has led to increasing research interest in evaluating the fatigue resistance of the friction-stirwelded joints, including the stress number of cycles to failure behavior [20,22,25,26] and fatigue crack propagation behavior. [7,18,19,21] Previous studies indicated the following results.…”

Section: Introductionmentioning

confidence: 99%

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Microstructure and Cyclic Deformation Behavior of a Friction-Stir-Welded 7075 Al Alloy

Feng

Chen

2010

Metall Mater Trans A

119

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Microstructural changes and cyclic deformation characteristics of friction-stir-welded 7075 Al alloy were evaluated. Friction stir welding (FSW) resulted in significant grain refinement and dissolution of g¢ (Mg(Zn,Al,Cu) 2 ) precipitates in the nugget zone (NZ), but Mg 3 Cr 2 Al 18 dispersoids remained nearly unchanged. In the thermomechanically affected zone (TMAZ), a high density of dislocations was observed and some dislocations were pinned, exhibiting a characteristic Orowan mechanism of dislocation bowing. Two low-hardness zones (LHZs) between the TMAZ and the heat-affected zone (HAZ) were observed, with the width decreasing with increasing welding speed. Cyclic hardening and fatigue life increased with increasing welding speed from 100 to 400 mm/min, but were only weakly dependent on the rotational rate between 800 and 1200 rpm. The cyclic hardening of the friction-stir-welded joints exhibiting a two-stage character was significantly stronger than that of the base metal (BM) and the energy dissipated per cycle decreased with decreasing strain amplitude and increasing number of cycles. Fatigue failure occurred in the LHZs at a lower welding speed and in the NZ at a higher welding speed. Fatigue cracks initiated from the specimen surface or near-surface defects in the friction-stirwelded joints, and the initiation site exhibited characteristic intergranular cracking. Crack propagation was characterized by typical fatigue striations along with secondary cracks.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microstructure and Cyclic Deformation Behavior of a Friction-Stir-Welded 7075 Al Alloy

Feng

Chen

2010

Metall Mater Trans A

119

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“…[19][20][21] From an engineering design perspective, fatigue properties of FSW aluminum alloys are of particular importance. This has led to increasing research interest in evaluating the fatigue resistance of friction-stir-welded joints, including stressnumber of cycles to failure (S-N) behavior [22][23][24][25] and fatigue crack propagation behavior. [6,[26][27][28] However, studies on the low-cycle fatigue (LCF) behavior of the friction-stir-welded aluminum alloys have been limited, [29][30][31] and they are indeed required by automobile manufacturers to estimate the lifetime of components.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and Low-Cycle Fatigue of a Friction-Stir-Welded 6061 Aluminum Alloy

Feng

Chen

2010

Metall Mater Trans A

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Strain-controlled low-cycle fatigue (LCF) tests and microstructural evaluation were performed on a friction-stir-welded 6061Al-T651 alloy with varying welding parameters. Friction stir welding (FSW) resulted in fine recrystallized grains with uniformly distributed dispersoids and dissolution of primary strengthening precipitates b¢¢ in the nugget zone (NZ). Two low-hardness zones (LHZs) appeared in the heat-affected zone (HAZ) adjacent to the border between the thermomechanically-affected zone (TMAZ) and HAZ, with the width decreasing with increasing welding speed. No obvious effect of the rotational rate on the LHZs was observed. Cyclic hardening of the friction-stir-welded joints was appreciably stronger than that of base metal (BM), and it also exhibited a two-stage character where cyclic hardening of the frictionstir-welded 6061Al-T651 alloy at higher strain amplitudes was initially stronger followed by an almost linear increase of cyclic stress amplitudes on the semilog scale. Fatigue life, cyclic yield strength, cyclic strain hardening exponent, and cyclic strength coefficient all increased with increasing welding speed, but were nearly independent of the rotational rate. Most friction-stirwelded joints failed along the LHZs and exhibited a shear fracture mode. Fatigue crack initiation was observed to occur from the specimen surface, and crack propagation was mainly characterized by the characteristic fatigue striations. Some distinctive tiremark patterns arising from the interaction between the hard dispersoids/inclusions and the relatively soft matrix in the LHZ under cyclic loading were observed to be present in-between the fatigue striations.

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“…This is clearly seen from Table 3.2, where data on mechanical properties of some nanostructured metallic materials produced via SPD are listed. However, a significant increase of this ratio was observed in some cases, for example, in the friction stir-processed AA7075 in [85] or in ECAP-processed Fe-36 % Ni Invar in [86]. Sometimes, standard thermo-mechanical processing might even lead to somewhat better HCF properties in the coarse-grained materials than in their nanostructured counterparts.…”

Section: High-cycle Fatigue Behavior Of Nanostructured Metallic Matermentioning

confidence: 99%

Multifunctional Properties of Bulk Nanostructured Metallic Materials

Sabirov

Enikeev

Murashkin

et al. 2015

Bulk Nanostructured Materials With Multifunctional Properties

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This chapter focuses on multifunctional properties of bulk nanostructured metallic materials and structure-properties relationship therein. The most important structural factors affecting mechanical, physical, and chemical properties of the nanomaterials are discussed, and the strategies to their further improvement are outlined. Special attention is paid to nanostructural design for simultaneous improvement of mutually exclusive properties. Superstrength and Enhanced Mechanical PropertiesAlthough the mechanical and functional properties of all polycrystalline metallic materials are determined by several factors, the grain size of the material generally plays the most significant and often a dominant role. Thus, the strength of different polycrystalline materials is related to the grain size, d, through the Hall-Petch equation which states that the yield stress, σ y , is given bywhere σ o is termed the friction stress and k y the Hall-Petch constant [1,2]. It follows from Eq. 3.1 that the strength increases with a reduction in the grain size and this has led to an ever-increasing interest in fabricating materials with extremely small grain sizes. The fabrication of bulk samples and billets using equal channel angular pressing (ECAP), high pressure torsion (HPT), and other severe plastic deformation (SPD) techniques was a crucial first step in initiating investigations into the properties of bulk nanomaterials because the use of SPD processing permitted, and subsequently fully supported, a series of systematic studies using various nanostructured metallic materials including commercial alloys [3][4][5][6][7][8]

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Effect of microstructure on fatigue life and fracture morphology in an aluminum alloy

Cited by 78 publications

References 8 publications

Microstructure and Cyclic Deformation Behavior of a Friction-Stir-Welded 7075 Al Alloy

Microstructure and Cyclic Deformation Behavior of a Friction-Stir-Welded 7075 Al Alloy

Microstructure and Low-Cycle Fatigue of a Friction-Stir-Welded 6061 Aluminum Alloy

Multifunctional Properties of Bulk Nanostructured Metallic Materials

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