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Highlights • The aluminium foam sandwich was fabricated using friction stir welding. • No undesirable interface reaction existed among the face sheets and the foam core. • AFS prepared through FSW possessed high flexural strength and impact resistance. • The AFS possessed good sound absorption and insulation performance. Abstract The aluminium foam sandwich (AFS), prepared through the traditional adhesive or brazing methods, usually exhibits a low flexural strength due to the poor combination among the face sheets and the aluminium foam core. In this work, a new method, named friction stir welding (FSW), was utilized to fabricate AFS. The results demonstrated that the joining of the face sheets and aluminium foam was achieved through the plasticized metal flow. In addition, the AFS prepared through FSW possessed high flexural strength and impact resistance, as well as good sound absorption and reduction performance. This demonstrated that the FSW was a good method to prepare AFS. [ABSTRACT FROM AUTHOR]

At present, the effect of the microstructure of friction stir lap welded (FSLW) dissimilar joints of Mg and Al alloys on fatigue crack initiation and propagation is not clear. In this article, the effects of the microstructure of FSLW dissimilar joints of AZ31 Mg and Al–Zn–Cu–Mg alloys are studied. The grain orientations of the crack initiation and propagation region were characterized by electron backscattering diffraction analysis. And the models for fatigue crack propagation in the different grain orientations were established. Based on the above experimental results, the initiation mechanisms of fatigue cracks were clarified, and the effects of grain orientations on crack propagation were revealed. The results showed that the crack initiation was caused by the simultaneous activation of the (0002, 2 1 ¯ 1 ¯ 0] basal slip and twinning in various directions by fatigue loading. The direction of crack propagation was dominated by the (0002)[ 2 ¯ 110] basal slip with (1 ¯ 012)[ 1 ¯ 01 1 ¯ ] twinning adjusting in the crack propagation zone. The cyclic effect of concentration and release of stress on the activation and termination of twins was the main reason for the zigzag path of crack propagation. • (0002, 2 1 ¯ 1 ¯ 0] basal slip and twinning in various directions caused crack initiation. • Crack propagation models with the different grain orientations were established. • Activation and termination of twins caused zigzag path during crack propagation. [ABSTRACT FROM AUTHOR]

The formation mechanism of intermetallic compounds (IMCs) during dissimilar friction stir lap welding (FSLW) of Mg and Al alloys, as well as the effects of IMCs on the shearing properties of FSLW joints, are still ambiguous and require clarification. In this study, FSLW dissimilar joints of AZ31 Mg alloys and Al–Zn–Cu–Mg alloys are investigated to clarify the formation mechanism of IMCs and their effect on the joint strength. Microstructures and shearing properties of the joints are characterized. The results showed that new phases of Al 12 Mg 17 , Al 3 Mg 2 , MgZn 2 , and Al 2 Cu are generated at the welding interface, and the original Cu 2 Mg phase is dissolved into the Al matrix during FSLW. Furthermore, the formation sequence of IMCs in the same binary system is affected by the effective enthalpy of formation, while it is related to the element concentrations in different binary systems. The order of IMC formation is as follows: Al 12 Mg 17 , Al 3 Mg 2 , MgZn 2 , and Al 2 Cu. During shearing deformation of the FSLW joint, the crack is initiated at the hook zone in the retreading side and propagated along the welding interface, where IMCs aggregate and the strain concentrates. The small lattice mismatch between the IMCs and the matrix improves their interfacial bonding strength, which increases in the following order: Al 12 Mg 17 and Al, Al 12 Mg 17 and Mg, Al 3 Mg 2 and Al, Al 3 Mg 2 and Mg, MgZn 2 and Al, MgZn 2 and Mg, Al 2 Cu and Al, Al 2 Cu and Mg, Cu 2 Mg and Mg, and Cu 2 Mg and Al. • Thermodynamics and atomic collision affected formation mechanism of IMCs. • Formation sequence of IMCs during FSLW was: Al 12 Mg 17 , Al 3 Mg 2 , MgZn 2 and Al 2 Cu. • Effects of IMCs on joint strength were analyzed by atomic lattice mismatch. • High lattice mismatches between matrices and Al 12 Mg 17 reduced joint strength. [ABSTRACT FROM AUTHOR]

• The incorporation of basalt fibers can improve the compressive strength of nano-SiO 2 cemented soils in both seawater and freshwater environments. • The addition of basalt fibers to nano-SiO 2 can effectively increase the unconfined compressive strength and ductility of cemented soil specimens in both freshwater and seawater environments. • Nano-SiO2 promotes the hydration reaction, leading to the formation of a greater amount of hydration products that encompass the basalt fibers, thereby enhancing the bonding and friction between the basalt fibers and the cemented soil. • Adding nano-SiO 2 to cemented soil blended with basalt fibers increases the optimum fiber content in marine environment to 0.3 %. In freshwater situations, an optimum fiber concentration is 0.6 %. • Seawater can boost soil compressive strength when early hydration products are scarce in cemented soil. However, seawater may diminish soil compressive strength if otherwise. The marine environment exposes cemented soils to a variety of adverse environmental conditions, which could substantially compromise the reliability and durability of foundations constructed on these engineered soils. Some researchers have recently proposed using nanoparticles to effectively strengthen and enhance the structure of cemented soil; however, this may compromise the ductility of cemented soils. Alternatively, some researchers have utilized basalt fibers to promote a stable network within the cemented soil by adding adhesion to the soil matrix, but this frequently results in a reduction in compressive strength. To address these issues, the addition of nanoparticles and basalt fibers to cement-treated soils is proposed as an engineering solution for extending the service life of cemented soils with adequate strength and durability in both freshwater and saltwater environments. This investigation utilized six different Nano-SiO2 concentrations and four different basalt fiber concentrations in the specimens. The specimens were then cured for 28 days in both freshwater and saltwater environments, and unconfined compressive strength tests (UCS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) experiments were performed to evaluate their properties, i.e. the microstructure, strength, and durability of cemented soil. The research results indicate that compared to conventional cemented soils, the improvement ratios after adding the optimal ratio of additives are 21 % (in freshwater environment) and 15 % (in seawater environment) for basalt fiber cemented soil, 196 % and 161 % for Nano-SiO 2 cemented soil, and 257 % and 214 % for Nano-SiO 2 /basalt fiber composite cemented soil. Nano-SiO 2 promotes the hydration reaction to generate more C-S-H, which wraps around the basalt fibers, enhances the bonding of basalt fibers in the cemented soil, effectively improves the mechanical properties and internal structure of the cemented soil, and the improvement effect is not weakened by seawater erosion. [ABSTRACT FROM AUTHOR]

Abstract Friction stir processing (FSP) followed by aging treatment is used to modify the microstructure and improve the mechanical properties of the as-cast AE42 rare earth-containing magnesium alloy. FSP results in grain refinement and microstructural homogenization. The grain size decreases from 81 to 7.4 μm because of continuous dynamic recrystallization. After FSP, basal texture forms, and Mg 17 Al 12 and Al 11 RE 3 phases disappear, while a new Al 2 RE phase appear. After aging treatment, precipitation of Al 2 RE phase appears and the intensity of texture reduce. Tensile properties of the FSP specimens exhibit an anisotropy obviously before and after the aging. Deformation mechanism of the FSP specimens follows the dislocation basal slip and the extension twin. Factors influencing strength of the as-cast AE42 Mg alloy are (a) secondary phases, (b) texture and (c) grain size. Highlights • Simultaneous improvement in ductility and strength occurred for specimens FSPed with aging heat treatment. • Factors influencing strength of the as-cast AE42 Mg alloy were (a) secondary phases (being the most affecting factor), followed by (b) texture and (c) grain size. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, static and electrochemical corrosion, and stress corrosion cracking (SCC) behavior of friction stir processed AZ80 magnesium alloy were investigated, and the effects of grain size and texture on the SCC were analyzed. The results showed that fine-grained (FG) and coarse-grained (CG) specimens with the average grain size of 2.7 and 7.1 μm was obtained via friction stir processing (FSP) underwater and in air, respectively. Both specimens exhibited the similar characteristics of basal texture. The average microhardness of FG specimen (75.3 HV) was higher than that of CG specimen (69.4 HV) in the stir zone. Grain refinement enhanced both the corrosion and stress corrosion resistances in 3.5 wt% NaCl solution. The FG specimen exhibited obvious anisotropy in SCC susceptibility when tested along the processing and transverse directions during slow strain rate tensile test. Texture softening effect accelerated the formation of pitting corrosion, and decreased the SCC performance. Fracture surface of SCC exhibited transgranular brittle fracture. SCC behavior was controlled by anodic dissolution, and the hydrogen accelerated the SCC. [ABSTRACT FROM AUTHOR]

In this work, friction stir welding (FSW) was used to weld dissimilar metals (Type 304 stainless steel (SS304) and Q235 low carbon steel). The microstructure, interfacial characteristics, residual stress distribution and mechanical properties of the joint were investigated. The results show that FSW results in grain refinement in the stir zone (SZ) and thermal-mechanical affected zone (TMAZ) in SS304 side. Discontinuous dynamic recrystallization and twinning-induced dynamic recrystallization are the main grain refinement mechanisms. Dynamic recovery occurs in the heat-affected zone (HAZ). On the Q235 steel side, the acicular ferrite and pearlite are generated in the SZ, which is due to its peak temperature of up to Ac 3. Additionally, the amount of acicular ferrite decreases in the TMAZ. Continuous and discontinuous dynamic recrystallization is the main recrystallization mechanism in the two regions. The interfacial bonding mechanism of FSW joint consists of both mechanical and metallurgical bonding. In addition, the difference in expansion coefficient and microstructure between the two steels results in the formation of residual compressive stress in the SZ. Grain refinement and acicular ferrite are responsible for the microhardness distribution in the whole joint. The tensile strength of FSW joint is 493 MPa, which is more than that of Q235 steel by around 4%. However, the elongation is 17%, which shows a decrease of around 50%. Furthermore, the fracture surface shows ductile fracture with dimples. • Recrystallization mechanism of dissimilar FSWed SS304 and Q235 steel was investigated. • Peak temperature of Q235 steel side during FSW was estimated. • Bonding mechanism welding joint is both mechanical and metallurgical bonding. [ABSTRACT FROM AUTHOR]