Application of the wavelet packet and its energy spectrum to identify nugget splash during the aluminum alloys spot welding

Nugget splash during aluminum alloys spot welding has a detrimental effect on weld nugget integrity, strength and durability of the welded joints. This investigation is performed to identify nugget splash from voltage signals because these are easily accessible on-line. In the present work, we propose a novel method based on the wavelet packet transform and its energy spectrum for pattern recognition of splash signal. The result demonstrates that this novel method is more accuracy and a useful way of monitoring the spot welding quality.

Corrosion behavior of the friction-stir-welded joints of 2A14-T6 aluminum alloy

The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy）, scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase（Al2Cu） after 2 h of immersion in EXCO solution.

Friction stir welding of high-strength aerospace aluminum alloy and application in rocket tank manufacturing

Friction stir welding （FSW） has been widely adopted in aerospace industry for fabricating high-strength aluminum alloy structures, such as large volume fuel tanks, due to its exceptional advantages includ- ing low distortion, less defects and high mechanical properties of the joint. This article systematically reviews the key technical issues in producing large capacity aluminum alloy fuel tanks by using FSW, including tool design. FSW process optimization, nondestructive testing （NDT） techniques and defect repairing techniques, etc. To fulfill the requirements of Chinese aerospace industry, constant-force FSW, retractable tool FSW, lock joint FSW, on-line NDT and solid-state equal-strength FSW techniques, as well as a complete set of aerospace aluminum FSW equipment, have been successfully developed. All these techniques have been engineered and validated in rocket tanks, which enormously improved the fabrication ability of Chinese aerospace industry.

Correlation Between Microstructure and Mechanical Properties of 2219-T8 Aluminum Alloy Joints by VPTIG Welding

In this study, 2219-T87 aluminum alloys were butt welded by the double-pass tungsten inert gas arc welding process. And the softening behavior of fusion zone（FZ） and heat-affected zone（HAZ） was evaluated with the analysis of welding temperature field, grain size, alloying element distribution and precipitates evolution. Results show that the two FZs are almost the weakest regions in the joint, where the microhardness value is 76 and 78 HV, respectively. Microhardness of the HAZ generally grows along with increasing distance from fusion line except a valley value at the distance of about 4.5 mm. The mean grain size of two FZs is about 74.4 and 79.2 lm, whereas 41.5, 44.9 and 43.4 lm for the two measured HAZs and base metal（BM）, respectively. There is about 60.4% and 54.2% Cu consumed in the coarse whitish particles of FZs that have little strengthening effect, while the percentage is about 24.6% of BM that is almost the same as HAZ. A large number of strengthening phases h0 distribute dispersively in BM, whereas hardly any precipitates exist in FZ and HAZ adjacent to FZ. So the coarsening of grain size, reduction and segregation of alloying element content, and the precipitate evolution are regarded as the main causes of softening in FZ, while the precipitate evolution is the main factor of softening in HAZ.

Effect of Sheet Configuration on Microstructure and Mechanical Behaviors of Dissimilar Al–Mg–Si/Al–Zn–Mg Aluminum Alloys Friction Stir Welding Joints

Friction stir welding（FSW） was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed.Results showed that rather different joint cross sections were obtained when using different sheet configurations.Coarser β＇ phases can be observed at the heat affected zone（HAZ） of the Al-Mg-Si alloy side,which was the main factor affecting the tensile properties and the fatigue properties.Tensile strengths of the dissimilar Al-Mg-Si/Al-Zn-Mg joints using both configurations were higher than that of the Al-Mg-Si FSW joint.When the Al-Zn-Mg alloy was located at the advancing side（AS）,the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.

Fabrication of large-bulk ultrafine grained 6061 aluminum alloy by rolling and low-heat-input friction stir welding

In this study, the ultrafine grained （UFG） 6061 Al alloys fabricated by cold rolling were friction stir welded （FSW） with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water （400-Water） could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG AI alloy by cold rolling with large deformation and low-heat-input FSW.

Improving Joint Features and Mechanical Properties of Pinless Fiction Stir Welding of Alcald 2A12-T4 Aluminum Alloy

As a new solid state welding,pinless friction stir welding（PFSW） can be used to join thin-wall structures.In this study,four new pinless tools with different groove distributions were designed and manufactured in order to enrich technological storage of PFSW and obtain sound joint with high quality of alclad 2A12-T4 alloy.The results show that the small-obliquity tool is detrimental to the transfer of plasticized materials,resulting in the formation of kissing bond defect.For the through-groove tool or the large-curvature tool,bigger flashes form on the joint surface and alclad layer is observed in the nugget zone（NZ）,deteriorating mechanical properties.Compared with the above-mentioned three tools,using the six-groove tool with rational curvature and obliquity can not only yield sound joint with small flashes and thickness reduction,but also prevent alclad from flowing into NZ,which has potential to weld thin alclad aluminum alloys.Meanwhile,the tensile strength and elongation of joint using the six-groove tool reach the maximum values of 362 MPa and 8.3%,up to 85.1% and 64% of BM.

Comparative study on local and global mechanical properties of bobbin tool and conventional friction stir welded 7085-T7452 aluminum thick plate

7085-T7452 plates with a thickness of 12 mm were welded by conventional single side and bobbin tool friction stir welding （SS-FSW and BB-FSW, respectively） at different welding parameters. The temperature distribution, microstructure evolution and mechanical properties of joints along the thickness direction were investigated, and digital image correlation （DIC） was utilized to evaluate quantitatively the deformation of different zones during tensile tests. The results indicated that heat-affected zone （HAZ）, the local softening region, was responsible for the early plastic deformation and also the fracture location for SS-FSW samples, while a rapid fracture was observed in weld nugget zone （WNZ） before yield behavior for all BB-FSW specimens. The ultimate tensile strength （UTS） of SS-FSW joints presented the highest value of 410 MPa, 82% of the base material, at a rotational speed of 300 rpm and welding speed of 60 mm/min, much higher than that of BB-FSW joints, with a joint efficiency of only 47%. This should be attributed to the Lazy S defect produced by a larger extent of heat input during the BB-FSW process, The whole joint exhibited a much higher elongation than the slices. Scanning electron microscopic （SEM） analysis of the fracture morphologies showed that joints failed through ductile fracture for SS-FSW and brittle fracture for BB-FSW.

Microstructure and Strain Hardening of a Friction Stir Welded High-Strength Al–Zn–Mg Alloy

Microstructural evolution and strain hardening behavior of a friction stir welded（FSWed） high-strength7075Al-T651 alloy were evaluated.The nugget zone was observed to consist of fine and equiaxed recrystallized grains with a low dislocation density and free of original precipitates,but containing uniformly distributed dispersoids.The strength,joint efficiency,and ductility of the FSWed joints increased with increasing welding speed.A joint efficiency of ＊91% was achieved at a welding speed of 400 mm/min and rotational rate of 800 r/min,while the ductility remained basically the same as that of the base metal.There was no obvious strain rate sensitivity observed in both base metal and welded joints.While both the base metal and FSWed joints exhibited stage III and IV hardening characteristics,the hardening capacity,strain hardening exponent,and strain hardening rate all increased after friction stir welding.

Dendritic Boundary Corrosion of AA2198 Weld Using Fiber Laser Welding with Al–Cu Filler Wire

The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaC1 solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical compo- nents and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al-Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat- affected zone with a compact protective film.

Cracking evolution behaviors of lightweight materials based on in situ synchrotron X-ray tomography： A review

Damage accumulation and failure behaviors are crucial concerns during the design and service of a critical component, leading researchers and engineers to thoroughly identifying the crack evolution. Third-generation synchrotron radiation X-ray computed microtomo- graphy can be used to detect the inner damage evolution of a large-density material or component. This paper provides a brief review of studying the crack initiation and propagation inside lightweight materials with advanced synchrotron three-dimensional （3D） X-ray imaging, such as aluminum materials. Various damage modes under both static and dynamic loading are elucidated for pure aluminum, aluminum alloy matrix, aluminum alloy metal matrix composite, and aluminum alloy welded joint. For aluminum alloy matrix, metallurgical defects （porosity, void, inclusion, precipitate, etc.） or artificial defects （notch, scratch, pit, etc.） strongly affect the crack initiation and propagation. For aluminum alloy metal matrix composites, the fracture occurs either from the particle debonding or voids at the particle/matrix interface, and the void evolution is closely related with fatigued cycles. For the hybrid laser welded aluminum alloy, fatigue cracks usually initiate from gas pores located at the surface or sub-surface and gradually propagate to a quarter ellipse or a typical semi-ellipse profile.