scholarly journals Tensile and Fatigue Analysis Based on Microstructure and Strain Distribution for 7075 Aluminum FSW Joints

Metals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1610
Author(s):  
Guoqin Sun ◽  
Xinhai Wei ◽  
Deguang Shang ◽  
Shujun Chen ◽  
Lianchun Long ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Fatigue Fracture ◽  
Strain Distribution ◽  
Fatigue Behavior ◽  
Base Material ◽  
Nugget Zone ◽  
Friction Stir ◽  
Tension Tests ◽  
Deformation And Fracture ◽  
Stress Ratios

In order to study on tensile and fatigue fracture mechanism of friction stir welded (FSW) joints, the tensile and fatigue behavior of FSW joints are studied based on the microstructure and strain distribution. The large plastic deformation and fracture occurred in the thermo-mechanically affected zone (TMAZ) on retreating side in tension tests. High contents of shear texture and small angle grain boundary reduce the tensile mechanical property of TMAZ material. The fatigue weak area for FSW joints is affected by the loading condition. The strain concentration in the welded nugget zone (WNZ) and base material makes the fatigue fracture liable to happen in these areas for the FSW joints under the stress ratios of 0.1 and −0.3. When the fracture occurred in WNZ, the crack initiation mainly occurred in clusters of hardened particles, while when the fracture happened in base material, the crack initiation mainly occurred near the pit. The crack in WNZ propagated in an intergranular pattern and the crack in the other areas extended in a transgranular mode, leading to a higher crack growth rate of WNZ than of other regions.

scholarly journals Very High Cycle Fatigue Crack Initiation Mechanism in Nugget Zone of AA 7075 Friction Stir Welded Joint

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Chao He ◽  
Kazuhiro Kitamura ◽  
Kun Yang ◽  
Yong-jie Liu ◽  
Qing-yuan Wang ◽  
...  
Keyword(s):  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Welded Joint ◽  
Cycle Fatigue ◽  
Nugget Zone ◽  
Initiation Mechanism ◽  
Friction Stir ◽  
Very High Cycle Fatigue ◽  
Aa 7075 ◽  
Very High

Very high cycle fatigue behavior of nugget zone in AA 7075 friction stir welded joint was experimentally investigated using ultrasonic fatigue testing system (20 kHz) to clarify the crack initiation mechanism. It was found that the fatigue strength of nugget zone decreased continuously even beyond 107 cycles with no traditional fatigue limits. Fatigue cracks initiated from the welding defects located at the bottom side of the friction stir weld. Moreover, a special semicircular zone could be characterized around the crack initiation site, of which the stress intensity factor approximately equaled the threshold of fatigue crack propagation rate. Finally, a simplified model was proposed to estimate the fatigue life by correlating the welding defect size and applied stress. The predicted results are in good agreement with the experimental results.

scholarly journals On the Fatigue Performance of Friction-Stir Welded Aluminum Alloys

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4246
Author(s):  
Sergey Malopheyev ◽  
Igor Vysotskiy ◽  
Daria Zhemchuzhnikova ◽  
Sergey Mironov ◽  
Rustam Kaibyshev
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Aluminum Alloys ◽  
Fatigue Behavior ◽  
Base Material ◽  
Fatigue Performance ◽  
Coarse Grained ◽  
Original Material ◽  
Friction Stir ◽  
Macro Scale

This work was undertaken in an attempt to ascertain the generic characteristics of fatigue behavior of friction-stir welded aluminum alloys. To this end, different alloy grades belonging to both the heat-treatable and non-heat-treatable types in both the cast and wrought conditions were studied. The analysis was based on the premise that the fatigue endurance of sound welds (in which internal flaws and surface quality are not the major issues) is governed by residual stress and microstructure. Considering the relatively low magnitude of the residual stresses but drastic grain refinement attributable to friction-stir welding, the fatigue performance at relatively low cyclic stress was deduced to be dictated by the microstructural factor. Accordingly, the fatigue crack typically nucleated in relatively coarse-grained base material zone; thus, the fatigue strength of the welded joints was comparable to that of the parent metal. At relatively high fatigue stress, the summary (i.e., the cyclic-plus residual-) stress may exceed the material yield strength; thus, the fatigue cracking should result from the preceding macro-scale plastic deformation. Accordingly, the fatigue failure should occur in the softest microstructural region; thus; the fatigue strength of the welded joint may be inferior to that of the original material.

Corrosion Resistance Evaluation and Effects of Prior Corrosion and Stress on Fatigue Behavior of Friction Stir Welded AA2024-T3

CORROSION ◽  
10.5006/2447 ◽  
2017 ◽  
Vol 74 (2) ◽  
pp. 169-180 ◽  
Author(s):  
Takao Okada ◽  
Shigeru Machida ◽  
Toshiya Nakamura
Keyword(s):  
Corrosion Resistance ◽  
Fatigue Life ◽  
Fatigue Behavior ◽  
Base Material ◽  
Corrosion Damage ◽  
Al Alloy ◽  
Line Energy ◽  
Friction Stir ◽  
Aspect Ratios ◽  
Corrosion Pits

The corrosion resistance of 2024-T3 (UNS A92024) Al alloy with no clad layer and that of friction stir welded (FSW) joint specimens fabricated from the same material were evaluated. The surfaces of both the alloy base material and FSW joint specimens were ground out before being exposed to a 3.0% sodium chloride solution at 60°C for 24, 48, 72, or 96 h. The corrosion pits on the base material samples were found to be randomly distributed, while those on the FSW joint were formed around the edge and center of the weld line. Energy dispersive x-ray spectrometry indicated constituent particles containing Mg at the grain boundaries in the thermomechanically affected zone and stir zone of the FSW joint; this Mg content aggravated the corrosion damage in those regions. The depth and volume of the corrosion pits in the FSW joint were greater than those in the base material. However, the aspect ratios of the corrosion pits in the base material and FSW were similar. Prior-corroded specimens were fatigue tested to evaluate the effect of corrosion damage. The fatigue life of the base material with corrosion damage was slightly shorter than that of the FSW joint specimens with corrosion damage, and the fatigue life of an uncorroded FSW joint specimen was more than 10 times longer than that of a corroded specimen. Thus, corrosion damage has a severely detrimental effect on fatigue life. Further, fracture surface observation revealed that the fracture origins in the FSW joint specimens tended to be multiple corrosion pits; however, the corrosion pits with the greatest depth or volume did not necessarily become fracture origins in the base material or FSW joints.

Nonuniformity of Mechanical Property in the Weld Zone of Friction Stir Welded 7050 Aluminum Alloy Joint

2011 ◽  
Vol 189-193 ◽  
pp. 3560-3563
Author(s):  
Yu Wen Tian ◽  
Fei Xu ◽  
Wen Ya Li ◽  
Zhong Bin Tang
Keyword(s):  
Mechanical Property ◽  
Aluminum Alloy ◽  
Elastic Modulus ◽  
Weld Zone ◽  
Base Material ◽  
Weld Nugget ◽  
Second Phase ◽  
Nugget Zone ◽  
Friction Stir ◽  
7050 Aluminum Alloy

The distribution of mechanical property in the weld zone of friction stir welded 7050 aluminum alloy joint along the plane perpendicular to the welding direction was experimentally investigated by the non-contact measurement method. The results show that the elastic modulus presents a W-shape distribution across the weld zone. The elastic modulus in the weld nugget zone is increased due to the grain refinement. In addition, the elastic modulus in the advancing side is slightly less than that in the retreating side possibly because of the relatively higher temperature in the advancing side during the welding process. The strength in the vicinity of weld center is decreased while the ductility is enhanced. The tensile strength and yield strength in the weld nugget zone and thermo-mechanically affected zone are significantly decreased while the elongation is increased due to the change of strengthening mechanism. In the heat affected zone the strength is decreased compared to the base material because the second phase grows up.

Microstructures and Properties of FSW Joints of AZ31B Mg Alloy

2011 ◽  
Vol 291-294 ◽  
pp. 855-859 ◽  
Author(s):  
Si Rong Yu ◽  
Xian Jun Chen
Keyword(s):  
Mechanical Properties ◽  
Heat Affected Zone ◽  
Welded Joint ◽  
Base Material ◽  
Alloy Sheet ◽  
Weld Nugget ◽  
Mg Alloy ◽  
Material Strength ◽  
Nugget Zone ◽  
Friction Stir

The extruded AZ31B Mg alloy sheet was welded with friction stir welding. The microstructures and mechanical properties of the welded joint were investigated. The results show that the grains in the weld nugget zone were small, uniform and equiaxed. The grains in thermo-mechanical affected zone were stretched and relatively small, but were not as small and uniform as those in the weld nugget zone. The grains in the heat-affected zone were relatively coarse. The fracture of the welded joint occurred mainly in the heat affected zone. The tensile strength of the welded joints was up to 257.4 MPa and was 87.9% of the base material strength. The microhardness in the weld nugget zone was higher. The microhardness in the thermo-mechanical affected zone and heat affected zone were lower than that in the weld nugget zone. The microhardness in the weld nugget zone increased from the upper surface to the bottom.

Microstructure and Mechanical Properties of Cu-Cr-Zr Alloy by Friction Stir Welding

2012 ◽  
Vol 602-604 ◽  
pp. 608-611
Author(s):  
Di Qiu He ◽  
Rui Lin Lai ◽  
Shao Hua Xu ◽  
Kun Yu Yang ◽  
Shao Yong Ye ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Friction Stir Welding ◽  
Rotation Speed ◽  
Base Material ◽  
Traverse Speed ◽  
Nugget Zone ◽  
Alloy Plate ◽  
Friction Stir ◽  
Microstructure And Mechanical Properties ◽  
Zr Alloy

In this study, Cu-Cr-Zr alloy joints are successfully fabricated by friction stir welding (FSW). Defect-free weld are produced on 12mm thick Cu-Cr-Zr alloy plate useing a non-consumable tool with a specially designed and shoulder with a constant rotation speed and a fixed traverse speed. The effect of friction stir welding (FSW) on the microstructure and mechanical properties of Cu-Cr-Zr alloy joints are investigated in details: The joints showed the presence of various zones such as nugget zone (NZ) and thermo-mechanically affected zone (TMAZ) and base metal (BM), the microhardness and the tensile strength of welded joints are lower than that of the base material.

scholarly journals Effect of Corrosion and Surface Finishing on Fatigue Behavior of Friction Stir Welded EN AW-5754 Aluminum Alloy Using Various Tool Configurations

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3121 ◽  
Author(s):  
Abootorab Baqerzadeh Chehreh ◽  
Michael Grätzel ◽  
Jean Pierre Bergmann ◽  
Frank Walther
Keyword(s):  
Climate Change ◽  
Aluminum Alloy ◽  
Fatigue Behavior ◽  
Salt Spray ◽  
Base Material ◽  
Fatigue Properties ◽  
Surface Finishing ◽  
Friction Stir ◽  
Stationary Shoulder ◽  
Root Surfaces

In this study, fatigue behavior of surface finished and precorroded friction stir welded (FSW) specimens using various tool configurations were comparatively investigated by the load increase method. The FSW using conventional, stationary shoulder and dual-rotational configurations was carried out by a robotized tool setup on 2 mm EN AW-5754 aluminum sheets in butt joint formation. After extraction of the specimens, their weld seam and root surfaces were milled to two different depths of 200 µm and 400 µm to remove the surface and the FSW tool shoulder effects. This surface finishing process was performed to investigate the effect of the surface defects on the fatigue behavior of the FSW EN AW-5754 aluminum alloy sheets. It was found that material removal from the weld and root surfaces of the specimens, increased the fracture stresses of conventional and dual-rotational FSW from 204 to 229 MPa and 196 to 226 MPa, respectively. However, this increase could not be detected in stationary shoulder FSW. Specimens with finished surfaces, which showed superior properties, were used in salt spray and cyclic climate change test to investigate the effect of corrosion on the fatigue behavior of FSW specimens. It was shown that cyclic climate change test reduced the fatigue properties of the base material, conventional, stationary shoulder and dual-rotational FSW approximately 1%–7%. This decrease in the fatigue properties was greater in the case of the salt spray test, which was 7% to 21%.

Fatigue and Fracture Mechanics Analysis of Friction Stir Welded Joints of Aerospace Aluminum Alloys Al-2195

2013 ◽  
Author(s):  
Muhammad A. Wahab ◽  
Vinay Raghuram
Keyword(s):  
Fatigue Life ◽  
Friction Stir Welding ◽  
Aluminum Alloys ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Interface Element ◽  
Aerospace Structures ◽  
Friction Stir ◽  
Stress Ratios

Friction-Stir-Welding (FSW) has been adopted as a major process for welding Aluminum aerospace structures. Aluminum (Al-2195) which is one of the new generations Aluminum alloys that has been used for the new super lightweight external tank for the space shuttle. NASA’s Michaud Assembly Facility (MAF) in New Orleans is continuously pursuing Friction-Stir-Welding (FSW) technologies in its efforts to advance fabrication of the external tanks of the space shuttles. The future launch vehicles which will have reusable mandates, for the structure to have good fatigue properties which prompts an investigation into the fatigue behavior of the friction stir welded aerospace structures. The butt joint specimens of Aluminum alloys (Al-2195 and Al-2219) are fatigue tested according to ASTM-E647. The effects of stress ratios, corrosion preventive compound (CPC), and periodic overloading on fatigue life is investigated. Scanning Electron Microscopy (SEM) is used to examine the failure surfaces and examine the different modes of crack propagation i.e. tensile, shear, and brittle modes. It is found that fatigue life increases with the increase in stress ratios; the fatigue life also increases from 30%–38% with the use of CPC; and the fatigue life could increase 8–12 times with periodic overloading; while the crack closure phenomenon predominates the fatigue fracture. Numerical analysis has been used to model fatigue life prediction scheme for these structures, the interface element technique with critical bonding strength criterion for formation of new surface has been used to model crack propagation. The linear elastic fracture mechanics stress intensity factor is calculated using FEA and the fatigue life predictions made using this method; and are within 10%–20% of the experimental fatigue life obtained.

scholarly journals Corrosion Fatigue Fracture Characteristics of FSW 7075 Aluminum Alloy Joints

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4196
Author(s):  
Qingna Ma ◽  
Fei Shao ◽  
Linyue Bai ◽  
Qian Xu ◽  
Xingkun Xie ◽  
...  
Keyword(s):  
Friction Stir Welding ◽  
Aluminum Alloys ◽  
Fatigue Fracture ◽  
Corrosion Fatigue ◽  
Weld Nugget ◽  
Fatigue Properties ◽  
Nugget Zone ◽  
Fracture Characteristics ◽  
Friction Stir ◽  
Secondary Cracks

The corrosion fatigue properties and fracture characteristics of friction stir welding joints of 7075 aluminum alloys were studied via corrosion fatigue tests, electrochemical measurements, and corrosion fatigue morphology and microstructure observations. The results show that the corrosion fatigue crack of the friction stir welding (FSW) joint of 7075 aluminum alloys originated in the junction zone between the thermomechanically affected zone and the weld nugget zone. The corrosion fatigue life of the joint decreased with increasing stress amplitude, with an S–N curve equation of lgN = 5.845 − 0.014S. Multiple crack sources were observed in the corrosion fatigue fracture. The main crack source originated from the corrosion pits at the interface between the thermomechanically affected zone and the weld nugget zone due to the influence of the coarse microstructure and the large potential difference between both zones. Corrosion morphologies of a rock candy block and an ant nest appeared in the crack propagation zone and the grain boundary of the weld nugget zone. In addition, fatigue speckles and intergranular fractures were observed, as well as brittle fracture characterized by cleavage steps and secondary cracks in the final fracture zone.

Fractographical Investigation on High-Cycle Fatigue Behavior of Direct Aging GH4169 Superalloy

2014 ◽  
Vol 789 ◽  
pp. 627-632 ◽  
Author(s):  
Li Zhang ◽  
Xue Ren Wu ◽  
Xin Yue Huang ◽  
Xu Dong Li
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Primary Source ◽  
Fatigue Loading ◽  
Cycle Fatigue ◽  
Direct Aging ◽  
Stress Ratios

The present work is aimed at the fatigue crack initiation behavior of the direct aging superalloy GH4169 at 650 °C. Un-notched specimens were tested under high-cycle fatigue loading with the two stress ratios of R = 0.1 and 0.5. Fracture surfaces were examined using field emission scanning electron microscopy (FESEM). Special attention is paid to the crack initiation sites. Two microstructure features in the fatigue crack initiation regions have been observed. One is obviously the feature of the Ti (C,N)-inclusions, and the other is some kinds of facets. The analysis on the facets was carried out by using energy dispersive spectra (EDS). It was found that the elements at the facets are similar to the matrix. However, some inclusions, Nb (C,N), have been found in the subsurface facets in a few specimens. Sometimes, fatigue lives of the specimens for the crack initiating from the inclusions are longer than those of cracks from the facets, depending on the size of inclusions and the depth from sample surface. Crack initiation for most of the specimens occurs at inclusions, and therefore inclusion is a primary source of crack initiation for this alloy.

Sign in / Sign up

Export Citation Format

Share Document