Electron Backscatter Diffraction Research Articles

Hydrogen-induced crack behavior of a precipitation-strengthened Ni50Cr20Co15Al10V5 high entropy alloy

The hydrogen-induced cracking behavior and mechanism of an L12-strengthened Ni50Cr20Co15Al10V5 high entropy alloy was evaluated using the tensile test after hydrogen charging. The microstructures and hydrogen-induced cracks were characterized by electron backscatter diffraction and electron channeling contrast imaging methods. The results revealed that hydrogen decreased the strain hardening rate and induced pronounced cracks, leading to significant degradation in elongation. After deformation, the local strain was concentrated in the precipitate-matrix interfaces. The precipitate-matrix boundary and the interior of precipitates were prone to hydrogen embrittlement, where hydrogen-induced cracks tended to propagate, attributing to the hydrogen-enhanced decohesion mechanism.

Influence of Ti element on the microstructure and crack of modulated WC-strengthened Ni-based alloy coatings by laser cladding

For laser cladding of WC reinforced Ni50A Ni-based alloy coatings can cause cracks and porosity. Cracks and pores will restrict the application and performance of the coating. In order to improve the crack condition of the coating, the influence of alloying element Ti on the crack was investigated by introducing it. Cracks in the coatings were eliminated. When the addition amount of Ti is 3wt%, the morphology and properties of the coating are the best. The phase composition, microstructure, elemental distribution and grain orientation of the coatings were characterised using X-ray Diffractometry (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometer (EDS), Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The hardness and abrasion resistance of the coatings were tested using microhardness tester and friction tester. The results show that a large number of second phases are present in the coating when Ti particles are not added. The introduction of Ti element disperses the localised stresses in the Ni50A-WC coating. The macroscopic morphology of Ni50A-WC coating was improved. The introduction of Ti reduced the area of the second phase within the coating. The introduction of Ti generated TiC/TiWC2 in situ. However, the introduction of Ti increased the dilution rate and decreased the strength of the coating. Therefore, the microstructure of the coating can be controlled and the macroscopic defects of the coating can be improved by adjusting the addition ratio of Ti elements.

Influence of particle deformation zone (PDZ) size on dynamic recrystallization and precipitation behavior of SiCp/Mg-5Zn material during hot compression

The influence of particle deformation zone (PDZ) size on dynamic recrystallization (DRX) and precipitation behavior of SiCp/Mg-5Zn material was investigated through the hot compression. First, the microstructure and microhardness of matrix in PDZ were characterized for SiCp/Mg after compression at room temperature. Then, the microstructure evolution of SiCp/Mg-5Zn materials with different PDZ size was analyzed by optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) after compressing different strains. The results show that a significant misorientation gradient was formed near the particle for SiCp/Mg after compression at room temperature, but which is smaller than that around the grain boundary. The addition of SiCp can promote DRX nucleation of Mg matrix, but the promotion effect of particles on DRX nucleation is less than that of grain boundaries for SiCp/Mg-5Zn material during the hot compression, which causes a decrease in the DRXed ratio of SiCp/Mg-5Zn material with increasing PDZ size. Moreover, the volume fraction and size of precipitated phase both decrease with increasing the PDZ size. The aim of this work is to provide a strategy to acquire Mg alloys with excellent mechanical performance by regulating the microstructure of Mg matrix.

Microstructure Evolution and Cryogenic Impact Toughness Changes in Ce‐Containing Novel Cryogenic High‐Mn Austenitic Steel Weld Metals under Different Heat Inputs

The Ce‐containing novel cryogenic high‐Mn austenitic steel weld metals under different heat inputs are prepared by submerged‐arc welding to provide a satisfactory welding parameter scheme and further optimize its cryogenic impact toughness. The effect of heat input on microstructure, inclusion, and cryogenic impact toughness of weld metals are investigated via optical, scanning electron microscopy, electron backscatter diffraction, electronic probe microanalyzer, and cryogenic impact test. The results show that the dendrite arm spacing, segregation ratio of Mn, Si, and C elements and average effective grain size of the weld metals gradually increase, and the proportion of high‐angle grain boundaries decrease with the heat input increase from 11.91 to 20.24 kJ cm−1. The type of inclusions of weld metal with different heat inputs are all Ce2O3 and Ce2O2S. The number density of inclusions decreases monotonically from 5976 to 4912 mm−2, while the average size increases from 0.32 to 0.45 μm with the heat input increased. The increase in heat inputs consistently decreases the mean cryogenic impact toughness of weld metals from 123 to 102 J. The higher proportion of high‐angle grain boundaries and finer inclusions at lower heat input play the critical role in improving the cryogenic impact toughness.

Kyanite-muscovite-dumortierite vein mineralization mechanisms from advanced microstructural analysis using EBSD

Abstract Dumortierite, an aluminous borosilicate mineral, is relatively rare in Earth’s crust, but it is the second most abundant aluminous borosilicate after tourmaline. Boron is an element with many uses in modern societies worldwide, from health products to wind turbine blades for clean energy, but of limited availability and at future risk of supply. Only a limited number of studies have been published on dumortierite mineralization processes and the factors that control its abundance and distribution remain poorly understood. Here we present the first comprehensive electron backscatter diffraction (EBSD) study of dumortierite mineralization mechanisms in kyanite-muscovite-dumortierite veins occurring in the metapelites of the Amgaon Gneiss Supracrustals, in the Girola hill area, Sakoli region, Central India. Advanced microstructural and chemical analyses show that mixed-mode brittle-viscous deformation in kyanite, by fracturing and easy glide on (100) [001] slip system, facilitates fluid-rock interactions with reactive hydrothermal fluids rich in B, F, and K and containing Na, Ti, Mg, Fe and Pt. These interactions cause the dissolution of kyanite along fracture and cleavage surfaces and the precipitation of muscovite (F = 0.32 wt %) and topaz (F = 16.48 wt %). The motion of ripplocation defects in muscovite facilitates fluid migration along cleavage surfaces and crystallisation of dumortierite needles within these surfaces. Fluid flux removes silica in solution from the system, so reactions may continue. The observed mineral assemblage, the microstructural signature of kyanite and muscovite, the moderate fluorine content of topaz, and low fluorine content of muscovite, together suggest that dumortierite mineralization results from hydrothermal activity, possibly in a transitional magmatic-hydrothermal environment, likely at P > 2.5 kbar and 400°<T < 550°, that could be linked with granite intrusions in the area. Using EBSD we demonstrate that dumortierite mineralization is focussed along muscovite basal cleavage surfaces and dumortierite needle elongation is likely controlled by the fluid flux direction. These new results advance our understanding of dumortierite mineralization mechanisms and conditions and have important implications for our understanding of the distribution of this aluminous borosilicate mineral in muscovite-rich rocks.

Atomistic simulation of primary microstructure formation in metals during crystallization from the melt.

Additive manufacturing of metallic parts by Selective Laser Melting (SLM) implies high temperature gradients and small volume of the melt bath. These conditions make the process scales close to those available for state-of-the-art massively parallel atomistic simulations. In the paper, the microscopic mechanisms responsible for the formation of primary microstructure during molten metal solidification are investigated using classical molecular dynamics (CMD). The 316L austenitic stainless steel with face centred cubic lattice, which is widely used in industry including SLM applications was chosen as a material for the CMD simulations. It was shown that solidified material inherits substrate defects and catches new ones, which interact with the solidification front thus producing the primary microstructure. Peculiarities of solidification in different crystallographic directions and solidification front interaction with grain boundaries and newly produced defects (mostly twin boundaries) as well as their formation are under study. Resulting microstructures of virtual samples are compared with those of real samples produced by SLM and analysed by the electron backscatter diffraction (EBSD) method. The comparison shows similarities of EBSD and CMD sample patterns and evidences for the capability of the large-scale atomistic simulations to reproduce main features of the microstructures formed in the metallic SLM additive production.

Study of microstructural evolution during operation of electrically connected components and analysis of failure mechanism

Abstract As a key current-carrying structure of high-voltage bushings, the reliability of electrical connection components is crucial to the safe and stable operation of power equipment. To obtain the microstructural evolution of electrical connection components with different deterioration states, CUD strap contactors were deteriorated in different ways, and electron backscatter diffraction technique was used to test the microstructure of strap contactors with different deterioration states. The results showed that compared to the unused contactors, the contact resistance of the contactors under the combined effect of friction and high temperature increased 203.12 times and was in a failed state. During the process from unused state to wear deterioration, high temperature deterioration, and then to eventual failure of the contactors, the average grain size gradually grows from 8.15 μm to 25 μm, the dislocation density gradually decreases from 2.38 × 1014 m−2 to 1.04 × 1014 m−2, and there are a significant proportion of the recrystallized organization. These changes are detrimental to the mechanical properties of the contactors. In addition, the distribution of grain boundaries in the contact area proves the occurrence of over-temperature phenomenon in this area, which will accelerate the deterioration of the contactors and eventually lead to the failure of the component. The relevant conclusions can provide a theoretical basis for the design of electrical connection structure of strap contacts as well as the study of deterioration mechanism.

Influence of Cold Drawing on Phase Transformation and Tensile Properties of FeCrMn Austenitic Stainless Steel 201

Manganese stabilizes the austenite and reduces the stacking fault energy in face‐centered cubic (FCC) structures, promoting the formation of hexagonal and cubic structures. This study investigates the phase transformation and mechanical behavior of extremely low‐carbon FeCrMn austenitic stainless AISI 201 steel subjected to cold drawing in three stages, ultimately reaching a true strain of 0.93. The objective is to examine the transformation from the parent FCC structure to hexagonal close‐packed and body‐centered cubic structures as a combination of transformation‐induced plasticity and twinning‐induced plasticity phenomena. X‐ray diffraction and electron backscatter diffraction analyses are utilized to investigate phase transformations under significant plastic deformation and the crystallographic orientation relationships between phases. Additionally, tensile and hardness tests are performed to assess the impact of plastic deformation on mechanical properties. Results indicate that a true strain of 50% is optimal for balancing strength and ductility in CrMnFe austenitic stainless steel. After applying a true strain of ε1 = 26.7%, yield strength (YS) increases by 192% and ultimate tensile strength (UTS) by 35%, while elongation reduces by 41%. With a further strain of ε2 = 57.5%, YS increases by 71% and UTS by 44%, but elongation drastically decreases by 94%. Applying the final strain of ε3 = 94.0%, YS and UTS only increase by 3% and 2%, respectively, while elongation further reduced by 40%. These findings suggest that a true strain of 50% shall be considered the maximum reduction for maintaining a balance between strength and ductility in CrMnFe austenitic stainless steel.

Magnetic Fabrics in Laminated Rocks of the Ilímaussaq Igneous Complex, Southern Greenland

ABSTRACT Nepheline syenites from the ∼1.2 Ga Ilímaussaq Complex of southern Greenland are examined to assess the utility of anisotropy of magnetic susceptibility (AMS) fabrics as proxies for silicate petrofabrics. Mineral lamination is a relatively common structural feature in cumulate rocks, including in the Ilímaussaq intrusion, but there is little consensus on the process (or processes) responsible for its formation. The Ilímaussaq AMS data are combined with rock magnetic experiments and electron backscatter diffraction (EBSD) measurements to characterize the magnetic mineralogy and compare the magnetic fabrics obtained to the silicate petrofabric. The data show that Na-amphibole (arfvedsonite) is most likely the dominant control on the AMS fabrics in the coarse-grained nepheline syenites (referred to as kakortokites), and that the AMS fabric is inverse relative to the observed silicate fabric. The EBSD data for a kakortokite sample suggests that the petrofabric is defined by arfvedsonite and is wholly planar, with evidence of only weak cross-lineation of c axes. The fine-grained nepheline syenites (lujavrites), two of which have a well-developed lamination carried by Na-pyroxene (aegirine), appear to have composite AMS fabrics that are considered to be a consequence of a mixed aegirine (normal) and arfvedsonite (inverse) response. The combined datasets shed light on the mechanisms of fabric acquisition in both lithologies. In the kakortokites, the AMS fabrics and silicate crystallographic preferred orientations, as well as the lack of observed microstructural evidence for subsolidus intra-crystal deformation, support models invoking gravitationally controlled crystal mats in the development of the macro-rhythmic layering of these rocks. In the lujavrites, the strong planar fabrics revealed by both the AMS and EBSD datasets, with some evidence of subsolidus deformation, point to fabric formation and perhaps even aegirine crystallization at the postcumulus stage. The combination of EBSD and AMS fabric datasets is a powerful means of deciphering the processes responsible for mineral alignment in igneous cumulates.

Short Crack Behavior of an Additively Manufactured Ti–6Al–4V Alloy Under Ultrasonic High Cycle Fatigue Testing

ABSTRACTThe high cycle fatigue (HCF) behaviors of an additively manufactured (AM) Ti–6Al–4V alloy with fully lamellar microstructures processed electron beam powder bed fusion (EB‐PBF) and wire‐fed electron beam directed energy deposition (Sciaky) routes were compared. Ultrasonic fatigue (USF) testing at the stress ratio of R = −1 was applied to monitor the growth of small cracks initiated at surface micronotches. Crack growth rates lower than 10−8 (m/cycle) at ΔK = 6 MPa·m1/2 were measured in samples processed by both methods. The finer α lath thickness (~1 μm) of the Sciaky samples resulted in a slower fatigue crack growth rate than the EB‐PBF samples with coarser laths. The interaction of cracks with the lamellar microstructures was characterized by electron backscatter diffraction. Crack propagation largely followed the lath interfaces in the Sciaky samples, whereas cracks cut across colonies in the EB‐PBF samples. Different fatigue fracture surface characteristics were observed for the EB‐PBF and Sciaky samples.

An in-situ investigation of microstructure neighborhood effects on hydrogen-induced dislocation activity

The interactions between hydrogen and crystallographic defects are the key to understanding hydrogen induced localized plasticity or damage mechanisms. However, unraveling such interactions based on the resulting mechanical effects alone can be challenging, due to the spectrum of various effects hydrogen can create in a given microstructure. Pre-deformation or post-mortem characterization of hydrogen segregation has similar limitations, as they can only provide snapshots of these complex processes with challenging spatial and temporal scales. To tackle this, we design in situ experiments that combine electron channeling contrast imaging (ECCI), electron backscattered diffraction (EBSD), and desorption spectroscopy, to investigate hydrogen defect interactions, under no external loading. We show that the inhomogeneous hydrogen distribution within microstructures can cause long-range (>200 nm) dislocation rearrangements. Interpretation of these results as manifestations of boundary-segregation induced stress suggests that microstructural characteristics on either side of the boundary should also play an important role. We provide quantitative assessments of these microstructure neighborhood effects and discuss additional contributions from hydrogen-induced changes in stacking fault energy and elastic modulus.

Effect of aging temperature on the microstructural evolution and mechanical properties of 18Ni (200) maraging steel

Herein, we used transmission electron microscopy (TEM), electron backscattering diffraction (EBSD), and X-ray diffractometry (XRD) to investigate the effects of different aging temperatures on reversed austenite and precipitates in 18Ni (200) maraging steel, as well as their evolving patterns of cryogenic toughness and strength. Aging at 510 °C was found to enhance cryogenic toughness at −196 °C and deliver peak strength, which is attributable to the significant aging-strengthening effect and the reversed austenite. Furthermore, this study investigated the factors that contribute to the formation and high stability of reversed austenite and quantitatively assessed the contributions of aging strengthening, dislocation strengthening, and grain-boundary strengthening to yield strength at various aging temperatures.

Microstructures, crystallography and growth patterns of serpulid tubeworms (Class Polychaeta)

Serpulid polychaetes are marine worms that secrete calcium carbonate tubes in which they live. Despite extensive previous research on their microstructures, there are no crystallographic data and their biomineralization process remains unclear. Here, the microstructures of the tubes of seven serpulid species were studied, including their chemical composition, mineralogy and crystallography, using X-ray diffraction, Raman and Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, focused ion beam, electron backscatter diffraction, and thermogravimetric analysis. Generally, serpulid tubes have a high amount of organic matter (~ 7.5 wt%), consisting of chitin and proteins, and the calcite is always present as medium to high magnesium calcite. Three main microstructures were identified: granular-prismatic and lamello-fibrillar calcite, and fibrous aragonite. They all displayed an axial texture, which is stronger in the lamello-fibrillar calcite, with the c-axis aligned with the elongation axis of the crystals. These findings demonstrate that only some instances of the granular-prismatic and the lamello-fibrillar calcite are biogenic (primary) microstructures. Conversely, other instances of the granular-prismatic calcite and the fibrous aragonite are a consequence of a recrystallization process (i.e. secondary). Replacement may occur on either primary or secondary calcitic microstructures (replaced by aragonite). Secondary microstructures retain remnants of the previously replaced microstructures, such as vestigial crystals or major growth increments. The high-Mg nature of the calcite favors recrystallization. The plywood arrangement of the lamello-fibrillar calcite is hypothesized to result from the ordering of a chitin fibrillar precursor into a cholesteric liquid crystal phase, with the calcite subsequently growing by oriented nucleation onto the organic fibrils.

Hot Uniaxial Pressing and Pressureless Sintering of AlCrCuFeMnNi Complex Concentrated Alloy—A Comparative Study

External pressure is often applied during sintering to obtain materials with improved properties. For complex concentrated alloys (CCAs), this processing step is commonly performed in vacuum. However, this can promote the evaporation of elements and increase the oxide content, thereby degrading the properties of the alloy. In this study, we compared the microstructures and properties of AlCrCuFeMnNi CCA samples obtained by hot uniaxial pressing sintering (HPS) and pressureless sintering (PLS) using a helium atmosphere purified by an oxygen getter system. The powders were prepared from mixtures of CrFeMn, AlNi and Cu and sintered by HPS at 900 °C for 1 h with an applied pressure of 30 MPa and by PLS at 1050 °C for 1 h. The samples were characterised using X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattering diffraction, density measurements and hardness tests. It was found that the oxygen getter system promoted oxygen partial pressure values at sintering temperatures similar to those of a mixture of 90% helium and 10% hydrogen. The HPS allowed us to obtain almost fully dense samples with a smaller average grain size and finer distribution of aluminium oxides than PLS. These differences increased the hardness of the samples sintered under pressure.

Effect of laser cladding layers on microstructure and mechanical properties of NiCoCrAlY bond coat

The NiCoCrAlY alloy is usually used as a bonding layer material in thermal barrier coatings (TBCs) system. Owing its excellent high-temperature oxidation resistance and corrosion resistance, it plays a crucial role in maintaining the structural integrity and functionality of TBCs. Laser cladding technology is a flexible and efficient processing technique for the manufacturing of NiCoCrAlY bond coat, with the characteristics of precisely control the layers of the laser cladding and further modulate the quality of the bond coat. Therefore, the investigation on the influence of cladding layers on the microstructure and mechanical properties of the bond coat is of great significance for improving the service performance and lifetime of aircraft engines. To this end, the scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) were used in this study to explore the influence of cladding layers on the microstructure and mechanical properties of the NiCrAlCoY bond coat. The results indicate that the microstructure of the cladded alloy can be divided into substrate, heat-affected zone, and cladded zone. The hardness of both the heat-affected zone and the cladded zone increases as the number of cladding layers increases, while the hardness of the substrate maintains constant. In addition, as the number of laser cladding layers increases, so does the residual stress of the cladded alloy.

Mechanistic understanding of banded microstructure and its effect on anisotropy of toughness in low carbon-low alloy steel

In this study, the relationship between the anisotropy of toughness and microstructure in low carbon low alloy steel treated by quenching and tempering (QT) heat treatment was investigated with the aid of scanning electron microscope, electron back-scattered diffraction and transmission electron microscope combined with energy disperse spectroscopy techniques. Results show that the impact toughness of the quenched steel plate along the longitudinal and transverse directions are little different. However, after tempering, the longitudinal impact toughness of QT steel plate is improved by 88 %, while the transverse impact toughness is slightly decreased, leading to a significant anisotropy of toughness. Microstructural characterizations reveal that banded microstructure with coarse grain size exists along longitudinal direction (i.e., rolling direction) of steel plate, which is attributed to co-segregation of Mn and C and the resulting uneven recrystallization during hot rolling. After tempering, fine and dispersed carbides are precipitated in matrix microstructure, but high-density coarse carbides are formed within banded microstructure. It is suggested that the coarse grains and high-density coarse carbides significantly deteriorate the resistance against crack propagation along banded microstructure, leading to the anisotropy of toughness of QT steel plate. The findings of this study will aid to design metallurgical processes including chemical composition design, hot rolling, and heat treatments to eliminate the anisotropy of toughness of low alloy steels with high strength and toughness.

Microstructural evolution, crystallographic texture, grain morphology, and mechanical integrity of wire arc additively manufactured Inconel 625 alloy

The material in wire arc additive manufacturing (WAAM) undergoes complex material flow and multiple thermal heating and cooling cycles, forming highly heterogeneous microstructures in terms of size, crystallographic orientations, and mechanical properties. The inhomogeneity also depends on the dislocation density and phases, which are influenced by the thermal history of the process. In this study, the Cold Metal Transfer (CMT) process was used to deposit a 60-layer build of Inconel 625 alloy. Detailed variations in the microstructural size, orientations, and phases along the building direction were studied using optical microscopy, electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). Microstructural observations reveal dendrites, equiaxed crystals, cellular, and columnar structures with primary and secondary dendrites. Dynamic recrystallization (DRX) followed by abnormal grain growth was found in the build. The average grain size varies with deposited height, with a grain size of around 13 ± 1 μm near the substrate, 45 ± 1 μm in the middle region, and 18 ± 1 μm at the top. The top region exhibited a strong intensity of recrystallized Cube, Cube-ND, and Cube-RD textures, with weaker intensities of copper and brass textures. The middle and bottom regions show strong intensities of Goss, copper, F, S, and E textures, respectively. The highest dislocation density of 5.122 × 10−4 nm−2 was found in the top region, while the lowest (4.14 × 10−4 nm−2) was observed in the bottom region. The ultimate tensile strength of the build ranged from 603 ± 05 MPa to 699 ± 10 MPa, while the yield strength varied from 313 ± 07 MPa to 365 ± 08 MPa along different orientations. Vickers hardness results showed a slight variation, from 240 ± 5 to 260 ± 2 HV, from bottom to the top of the deposited build. The findings from this study provide valuable insights into the microstructural evolution mechanism and mechanical behavior of WAAM-fabricated Inconel 625, which can guide other researchers in optimizing process parameters, enhancing material properties, and understanding the effects of thermal history on additive manufacturing of high-performance alloys.

Changes in Microstructure and Mechanical Properties of Goryeo Dynasty Bronze Vessels with Manufacturing Process

Bronze vessels are manufactured using casting and forging techniques, and various microstructures can be observed depending on the manufacturing process. In this study, we confirmed mechanical properties and microstructural evolution in the manufacturing process by observing the microstructures and composition analysis of 18 bronze vessels in the Goryeo Dynasty excavated from historical sites. The results show that 13 of the bronze vessels were manufactured using a Cu-Sn alloy with a Sn content of 20 to 24 wt%. The α phase and β(M) phase were observed, indicating that hot forging and quenching treatment were performed after casting. 3 bronze vessels were produced from a Cu-Sn-Pb alloy, and considering that the α phase and α+δ phase were observed, it could be seen that the process was completed by slow cooling after casting. The correlation between the type of bronze vessel and the manufacturing process has not been confirmed, except of ewer. It was confirmed that various microstructures were created depending on the manufacturing process and that the mechanical properties also changed. Bronze vessels composed of the α phase and α+δ phase due to the casting process had lower Vickers hardness values compared to bronze vessels that showed the quenched β(M) or γ phase. Electron backscatter diffraction (EBSD) phase analysis and kernel average misorientation (KAM) were performed using six bronze vessels composed of α and β(M) phases. The results showed that the factors affecting hardness were the ratio of the β(M) phase and the KAM value. However, it could not be confirmed to what extent the ratio of the β(M) phase and KAM value affected the improvement in mechanical properties.

Microstructure analysis and interfacial wave formation mechanism research of Mg/Al dissimilar metal laser impact welding in a vacuum environment

Laser impact welding (LIW) joints for the center exists springback region, resulting in a small effective welding area seriously affects the LIW joints performance problems. This paper for the first time put forward the vacuum environment LIW process, to carry out the vacuum environment of the two dissimilar lightweight metal magnesium/aluminum (Mg/Al) LIW. Results of the research showed that no springback occurred in the welded area. In order to reveal the vacuum environment LIW mechanism, the surface and cross-section morphological characteristics, weld interface microstructure, interface waveform element content and mechanical properties of laser impact welded Mg/Al dissimilar metals were investigated by optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD), energy spectrometry (EDS), and the universal testing machine. Studies have shown that the experimental success rate in the vacuum environment is much higher than that in the atmospheric environment, and the vacuum environment eliminates the springback cracking defect phenomenon generated in the center of the welded joints, which greatly increases the effective welding area of the weld. The number of Mg grain refinement in the interface region of the vacuum environment welding is more, and the bonding force of the two-plate welding is increased. Significant orientation differences, severe plastic deformation and high strain at the weld interface are one of the reasons for the successful LIW. Mg/Al welding samples produced elemental diffusion phenomenon, no obvious melting phenomenon, which is conducive to improving the welding quality. Tensile strength of the welded samples in the vacuum environment was higher than that in the atmospheric environment. Using the SPH-Lagrange coupling method, numerical simulations were carried out to study the trends shear stress, pressure, velocity, temperature and equivalent plastic strain distribution at the weld interface under vacuum environment, which revealed the interface wave formation mechanism in the center of laser impact welded joints with no springback cracking phenomenon. Vacuum laser impact welding opens up a new technology pathway for LIW of Mg/Al welded joints without springback in the center, which plays an important role in improving Mg/Al welding performance.

Quasi-in-situ observations of microstructural evolution during cyclic deformation of a Mg-Zn-Ca alloy

Quasi-in-situ electron backscatter diffraction (EBSD) was employed to investigate the microstructural evolution of a homogenized coarse-grained Mg-1.2Zn-0.1Ca alloy during cyclic deformation at a strain amplitude of 0.8 %. The random orientations of grains along with the soft state of the alloy resulted in symmetrical hysteresis loops and cyclic hardening. Besides the occurrence of twinning-detwinning, basal <a>/pyramidal II <c+a> and pyramidal I <a> slip systems were primarily activated. Grain boundaries with a higher misorientation angle of >35° served as preferential sites for strain localization.