Stability of nugget zone grain structures in high strength Al-alloy friction stir welds during solution treatment

Hassan, Kh.A.A; Norman, A.F.; Price, D. A.; Prangnell, P.B.

doi:10.1016/s1359-6454(02)00598-0

Cited by 260 publications

(122 citation statements)

References 12 publications

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“…As shown by Murr et al, Mahoney et al, and Hassan et al, [36][37][38] and as displayed in Figure 5, roughly equiaxed grains in the WN with a 5-to 10-lm grain size near the weld surface, decreasing to below 1 lm near the root, are present. The thermal gradient through the weld thickness, either influencing the initial recrystallized grain size or simply altering the extent of postweld grain growth, may be responsible for that.…”

Section: Resultsmentioning

confidence: 54%

Mechanical Tensioning of High-Strength Aluminum Alloy Friction Stir Welds

Altenkirch

Steuwer

Peel

et al. 2008

Metall Mater Trans A

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The extent to which in-situ global mechanical tensioning (GMT) can be used to modify the residual stress state in friction stir (FS) welds is investigated in this article. Residual stress distributions have been determined by synchrotron X-ray and neutron diffraction for four sets of FS welds in high-strength AA7449-W51 and lithium containing AA2199-T8 aerospace aluminum alloys subjected to a systematic range of GMT levels. For the cases studied, the results indicate that the level of residual stresses present in the as-welded state is a function of the alloy. The rate of residual stress reduction brought about by GMT, however, is basically alloy independent; indeed, it is essentially linear with respect to the GMT load, so that the tensioning required to reduce the weld stresses to zero can be calculated directly from the stresses present in the untensioned case. For thin plates, proximity to the yield stress in the hot-softened zone means that a guideline rule is that 1 MPa of tensioning during welding reduces the tensile stress by approximately 1 MPa. The GMT was found to be less effective at greater depths in thick plates. Furthermore, a reduction in bending distortion and an increase in angular distortion was observed with increased GMT, while no effects on the weld microstructure and hardness were observed.

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Section: Resultsmentioning

confidence: 54%

Mechanical Tensioning of High-Strength Aluminum Alloy Friction Stir Welds

Altenkirch

Steuwer

Peel

et al. 2008

Metall Mater Trans A

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“…The relationship between the Al 3 Zr dispersoids and the stability of the NZ grain structures in the friction-stir-welded AA7010-T7651 alloy has been well studied in detail. [55] B. Microhardness Profile It was reported that the hardness profile of frictionstir-welded heat-treatable aluminum alloys greatly depended on the precipitate distribution and only slightly on the grain and dislocation structures. [56] In the precipitation-hardened aluminum alloys, FSW resulted in a softened region in the HAZ, which was basically characterized by the dissolution/coarsening of precipitates during the FSW thermal cycle.…”

Section: Number Of Cycles Nmentioning

confidence: 99%

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

Feng

Chen

2010

Metall Mater Trans A

121

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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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“…Humphreys [52] proposed a theory of recrystallization which could be used to analyze the influence of second-phase particles on abnormal grain growth. Hassan et al [19] applied Humphreys' model to AA7010 alloy and believed that a grain size of at least 10 μm in the nugget zone was required for 7xxx aluminum alloys to avoid AGG during solution treatment because of the insufficient quantity of the thermal precipitates needed for the pinning effect. In this work, the FSP-treated PR alloys with a grain size of around 2-3 μm exhibited good thermal stability during the following T6 treatment, no AGG was observed, although a high solution temperature of 475 °C was chosen.…”

Section: Thermal Stability Of the Microstructurementioning

confidence: 99%

“…In addition, FSP is regarded as a promising grain refinement technique [14][15][16][17]. However, microstructural instability at elevated temperatures is found to be a crucial problem in aluminum alloys with a fine grain size [18,19], thus the improvement of the final strength of those alloys is limited [20,21]. For example, Moradi et al [22] studied the AA6061-AA2024 friction stir welding butt joint and found that abnormal grain growth occurred in the nugget zone.…”

Section: Introductionmentioning

confidence: 99%

Microstructure of Multi-Pass Friction-Stir-Processed Al-Zn-Mg-Cu Alloys Reinforced by Nano-Sized TiB2 Particles and the Effect of T6 Heat Treatment

Zhang

Chen

et al. 2017

Metals

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Abstract:In this work, a fine-grained structure with a uniform distribution of TiB 2 particles and precipitates was achieved in TiB 2 particle-reinforced (PR) Al-Zn-Mg-Cu alloys by friction stir processing (FSP). The effects of multi-pass FSP on the microstructure, and TiB 2 particle distribution, as well as the microstructural evolution in the following T6 treatment, were investigated by X-ray diffraction, scanning electron microscopy and associated electron backscattered diffraction. The results showed that the distribution of TiB 2 particles and alloy precipitates was further improved with an increase in the FSP passes. Moreover, compared with alloy segregation in the as-cast PR alloys during T6 treatment, a complete solution of the precipitates was achieved in the FSP-treated PR alloys. The fine-grained structure of the FSP-treated PR alloys was thermally stable without any abnormal growth at the high temperature of T6 treatment due to the pinning effect of dispersed TiB 2 particles. The strength and ductility of the PR alloys were simultaneously improved by the combination of FSP and T6 treatment.

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Stability of nugget zone grain structures in high strength Al-alloy friction stir welds during solution treatment

Cited by 260 publications

References 12 publications

Mechanical Tensioning of High-Strength Aluminum Alloy Friction Stir Welds

Mechanical Tensioning of High-Strength Aluminum Alloy Friction Stir Welds

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

Microstructure of Multi-Pass Friction-Stir-Processed Al-Zn-Mg-Cu Alloys Reinforced by Nano-Sized TiB2 Particles and the Effect of T6 Heat Treatment

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