Improvement in fatigue properties of 2024-T351 aluminum alloy subjected to cryogenic treatment and laser peening

Laser shock peening has established itself as an effective surface treatment to enhance the fatigue properties of metallic materials. Although a number of works have dealt with the formation of residual stresses, and their consequent effects on the fatigue behavior, the influence of material geometry on the peening process has not been widely addressed. In this paper, Laser Peening without Coating (LPwC) is applied at the surface of a notch in specimens made of a 6082-T6 aluminum alloy. The treated specimens are tested by three-point bending fatigue tests, and their fatigue life is compared to that of untreated samples with an identical geometry. The fatigue life of the treated specimens is found to be 1.7 to 3.3 times longer. Brinell hardness measurements evidence an increase in the surface hardness of about 50%, following the treatment. The material response to peening is modelled by a finite element model, and the compressive residual stresses are computed accordingly. Stresses as high as −210 MPa are present at the notch. The ratio between the notch curvature and the laser spot radius is proposed as a parameter to evaluate the influence of the notch.

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Effects of laser peening treatment on high cycle fatigue properties of degassing-processed cast aluminum alloy

Materials Science and Engineering A ◽

10.1016/j.msea.2006.09.126 ◽

2007 ◽

Vol 468-470 ◽

pp. 171-175 ◽

Cited By ~ 36

Author(s):

Kiyotaka Masaki ◽

Yasuo Ochi ◽

Takashi Matsumura ◽

Yuji Sano

Keyword(s):

Aluminum Alloy ◽

High Cycle Fatigue ◽

Fatigue Properties ◽

Cast Aluminum Alloy ◽

Laser Peening ◽

Cycle Fatigue ◽

Cast Aluminum

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The Fatigue Properties of Laser Shock Processed Aluminum Alloy 7050

Volume 6: Materials and Fabrication ◽

10.1115/pvp2007-26047 ◽

2007 ◽

Author(s):

Shikun Zou ◽

Ziwen Cao

Keyword(s):

Residual Stress ◽

Aluminum Alloy ◽

Fatigue Life ◽

Plastic Strain ◽

Base Material ◽

Fatigue Properties ◽

Hole Drilling ◽

Drilling Process ◽

Laser Peening ◽

Laser Shock

In order to develop the application of laser shock processing (also named laser peening or LSP in short) as a strengthening technology for 7050 aluminum alloy fastener holes, the fatigue properties of laser shock-processed aluminum alloy specimens were investigated. At first, the dislocation density and surface residual stress induced in the shock affected zone was characterized and compared with that of the base material. Then, the fatigue specimens with stress-concentration hole (notch) were treated by LSP. The fatigue life of LSP-treated specimens were measured and compared with that of specimens made from base material without LSP. Fatigue tests were taken under special flight spectrum loading condition for mid-airframe. The results indicated that laser peening improved the fatigue life of all specimens tested. Specimens treated by LSP before hole-drilling had longer fatigue life than those specimens treated by LSP after hole-drilling. At last, the difference of both sequences was investigated by analyzing the plastic strain and residual stress induced by LSP. LSP induced both plastic strain and deformation at the surface layer. The plastic strain induced by LSP was shown to produce harmful orifices with sharp-angle near the edge of hole. The residual stress induced by LSP appears to remain compressive even after the hole-drilling process. In average, the fatigue life of specimens treated by LSP before hole-drilling was found to be 173% longer than that of untreated samples and approaching the life enhancement factor demonstrated by rod extrusion method (on specimens with large diameter holes).

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Effects of Laser Peening with a Pulse Energy of 1.7 mJ on the Residual Stress and Fatigue Properties of A7075 Aluminum Alloy

Metals ◽

10.3390/met11111716 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1716

Author(s):

Yuji Sano ◽

Kiyotaka Masaki ◽

Yoshio Mizuta ◽

Satoshi Tamaki ◽

Tomonao Hosokai ◽

...

Keyword(s):

Aluminum Alloy ◽

Pulse Energy ◽

Laser Pulses ◽

Microchip Laser ◽

Fatigue Properties ◽

Laser Peening ◽

Robot Arm ◽

X Ray Diffraction ◽

Bending Fatigue ◽

Laser Peening Without Coating

Laser peening without coating (LPwC) using a palmtop-sized microchip laser has improved the residual stresses (RSs) and fatigue properties of A7075 aluminum alloy. Laser pulses with a wavelength of 1.06 μm and duration of 1.3 ns from a Q-switched Nd:YAG microchip laser were focused onto A7075 aluminum alloy samples covered with water. X-ray diffraction revealed compressive RSs on the surface after irradiation using laser pulses with an energy of 1.7 mJ, spot diameter of 0.3 mm, and density of 100–1600 pulse/mm2. The effects were evident to depths of a few hundred micrometers and the maximum compressive RS was close to the yield strength. Rotation-bending fatigue experiments revealed that LPwC with a pulse energy of 1.7 mJ significantly prolonged the fatigue life and increased the fatigue strength by about 100 MPa with 107 fatigue cycles. The microchip laser used in this study is small enough to fit in the hand or be mounted on a robot arm. The results may lead to the development of tools that extend the service life of various metal parts and structures, especially outdoors where conventional lasers are difficult to apply.

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Improvement in Fatigue Strength of Friction Stir Welded Aluminum Alloy Plates by Laser Peening

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.891-892.969 ◽

2014 ◽

Vol 891-892 ◽

pp. 969-973 ◽

Cited By ~ 1

Author(s):

Yuji Sano ◽

Kiyotaka Masaki ◽

Keiichi Hirota

Keyword(s):

Aluminum Alloy ◽

Fatigue Strength ◽

Fatigue Testing ◽

Large Deviation ◽

Fatigue Cracks ◽

Weld Zone ◽

Base Material ◽

Fatigue Properties ◽

Laser Peening ◽

Friction Stir

Plane bending fatigue testing was performed to study the fatigue properties of friction stir welded (FSW) 3 mm thick AA6061-T6 aluminum alloy plates. Fatigue cracks propagated with bends and curves on the specimens, showing large deviation from a linear line. This might be reflecting the material flow and microstructure in the weld zone. The fatigue strength of the unwelded base material (BM) was 110 MPa at 107 cycles and FSW deteriorated it to 90 MPa. However, laser peening (LP) restored the degraded fatigue strength up to 120 MPa which is higher than that of the BM.

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