L. Zhai

Bio: L. Zhai is an academic researcher from Yanshan University. The author has contributed to research in topics: Surface layer & Roll bonding. The author has an hindex of 1, co-authored 1 publications receiving 23 citations.

Microstructure, texture and mechanical properties of Al/Al laminated composites fabricated by hot rolling

Abstract: AA 1060/3003/1060 laminated composites were fabricated by hot-roll bonding. The effect of rolling temperature on the microstructure, texture and mechanical properties of AA 1060/3003/1060 laminated composites was investigated. The results show that the development of microstructure and texture through the thickness of Al layers was inhomogeneous in the Al/Al laminated composites. Initial grains were elongated along the direction of about 15° to the RD in the region near the surface layer of AA 1060 aluminum alloy, and the incline angle gradually decreased as the measured position moved towards the interface of 1060/3003 from the surface layer. The rolling texture of 1060 layer consisted of the r-cube and γ-fiber shear textures and the remaining cube component. The r-cube shear texture weakened gradually as the measured position moved towards the interface of 1060/3003 from the surface layer, whereas the center layer of AA 1060 aluminum alloy had the strongest γ-fiber shear texture. The interface layer of AA 3003 aluminum alloy had a completely different texture from the center layer. For the Al/Al laminated composites, the YS and UTS first increased to a maximum value at about 200 °C and then decreased with increasing rolling temperature.

Influence of multi-pass rolling and subsequent annealing on the interface microstructure and mechanical properties of the explosive welding Mg/Al composite plates

Abstract: In this study we investigated the effect of multi-pass rolling and post-rolling heat treatment upon the microstructure at interface and mechanical properties of the explosive welding Mg/Al composite plates. The thin explosive welding Mg/Al composite plates with 2.14 mm in thickness and good surface quality were obtained by 5 passes hot rolling (30% reduction, 400 °C). To meet the requirement of subsequent forming, annealing process was performed. The results indicate that the thickness of interfacial diffusion layer increases with the increase of annealing temperature and holding time. The mechanical properties of composite plates increase first and then decrease with the increase of annealing temperature and holding time. The tensile strength and elongation of the composite plates under 200 °C/2 h annealing condition reach the maximum, which are 285 MPa and 24.5% respectively. Fracture surface morphology indicates that the post-rolling or annealed composite plates all exhibit mixed-mode of ductile and brittle fractures.

Al-Mg-Si/SiC laminated composites: Fabrication, architectural characteristics, toughness, damage tolerance, fracture mechanisms

Abstract: Different architectures of layered laminates comprising two exterior layers of Al-Mg-Si/SiC metal matrix composite and an Al1050 ductile interlayer were fabricated by means of hot roll-bonding with applying different strains of er = 39%, 51%, and 63%. For monolithics production, ceramic particulate reinforcement contents of 0, 5, 10, and 15 vol% were utilized. The aim of introducing ductile metal interlayer was to compensate the low toughness of composite layers and consequently enhancement of damage tolerance of bundled structures along with prevention of their catastrophic failure through activation of extrinsic toughening mechanism. Effects of architectural characteristics and fabrication routes on toughness and fracture behavior of materials were studied by mechanical examinations including three-point bending (3PB) and shear tests. Fracture surfaces of 3PB examination were studied by SEM while associated mechanisms and correlations with debonded area (delamination), deformability, and SiC content were disclosed and discussed. Different analyses by deriving σm were performed and the role of reinforcement content, lamination and er were defined. Deformability of fabricated materials by identifying et, ei, and ep parameters were discussed. Based on results, et trend was obeyed ep rather than ei due to more ep contribution in materials' total ductility. Toughness change by accounting initiation and propagation values were surveyed considering the combined effects of σm, elongation, and stress-bearing capacity. Eventually, it was inferred that toughness was strongly controlled by elongation alteration. In addition, the contribution of propagation was more highlighted rather than initiation for laminates. Based on fracture surfaces, in monolithic samples, fracture morphology associated with SiC concentration. Fracture morphology of exterior composite layers had not been affected by er in laminates; since interlayer fracture was strongly influenced by rolling. This was due to distinct involved failure mechanisms. Al1050 deformability was governed by delamination length as an indication of constraint level. Interfacial strength which acquired by shear test revealed that composite laminates had not been influenced by er due to the weak bondings of layers beside presence of SiC particles; however, aluminum laminates showed enhanced shear strength.

Investigation of microstructure and texture evolution of a Mg/Al laminated composite elaborated by accumulative roll bonding

Abstract: The microstructure and texture of an Al1050/AZ31/Al1050 laminated composite fabricated by accumulative roll bonding at 400 °C up to 5 cycles are investigated using Electron BackScatter Diffraction, neutron diffraction, microhardness measurements and tensile tests. EBSD analysis has shown that ARB processing led to microstructural refinement with equiaxed grain microstructure in AZ31 layers and to the development of elongated grains parallel to the rolling direction in Al 1050 layers. No new phases formed at the bond interface after the first ARB cycle while Mg17Al12 and Mg2Al3 phases appeared after subsequent cycles. During the ARB processing, a typical strong basal (0002) texture is observed in AZ31 layers along with a weak rolling texture showed in Al 1050 layers with a dominant Rotated Cube {001}〈110〉 component. The microhardness of Al1050/AZ31/Al1050 laminated composite increased with increasing ARB cycles and almost saturated after five ARB cycles. The yield strength and ultimate strength increased gradually between 1 and 3 ARB cycles due to the strain hardening and grain refinement. They decreased with further increasing of the ARB cycles because of crack and failure of the MgxAly intermetallic compounds which developed during 4th and 5th ARB cycles. The deformation behavior of the laminated composite becomes rather similar to the behavior of AZ31 alloy that underwent a dynamic recrystallization during processing.

Microstructure development and texture evolution of aluminum multi-port extrusion tube during the porthole die extrusion

Abstract: Aluminum multi-port extrusion tube is processed by the porthole die extrusion and the internal tube walls are welded through the solid state metallurgical bonding. In order to observe the development of grains and their orientations under severe plastic deformation and solid state welding, the extrusion butt together with the die is quenched immediately after extrusion to preserve the grain structure in the processing. The forming histories of selected material points are obtained by analyzing the optical microscopy graph. The evolution of the microstructure along the forming path is characterized by electro backscattered diffraction. It is found that geometrical dynamic recrystallization happens in the process. Grains are elongated, scattered at the transition zone and shear intensive zone, and then pinched off when they are pushed out from the die orifice. The shear-type orientations are predominant at the surface layer on the longitudinal section of the tube web and have penetrated into the intermediate layer. The rolling-type orientations are formed at the central layer. Texture gradient through the thickness of the tube web is observed. And cube orientated grains are found at the seam weld region.

Effect of annealing on the microstructures and mechanical properties of Al/Mg/Al laminates

Abstract: Al/Mg/Al laminates were fabricated by hot rolling at 400 °C and annealed at temperature ranging from 200 °C to 400 °C for 1 h to 4 h. Microstructural examination revealed that brittle intermetallics identified as Mg17Al12 and Al3Mg2 appeared at Mg/Al interface when annealing temperature exceeded 300 °C. Al layers in laminates annealed at 200 °C exhibited typical copper-type texture, which totally transformed to recrystallized cube texture at 400 °C with a higher intensity. Mg layers in annealed laminates presented (0002) basal texture with c-axis titling from normal direction (ND) to rolling direction (RD), and bimodal basal texture was observed at 400 °C. Recrystallization extent of Mg layer increased with the increase in annealing temperature and/or annealing time, and nuclei preferred to occur in grains near Mg/Al interface. Grain size, texture type of matrix, and thickness of intermetallic layers all influence mechanical properties of Al/Mg/Al laminates. Laminates annealed at 200 °C for 1–4 h exhibited better ultimate tensile strength (UTS) ranging from 223 MPa to 240 MPa and elongation (EL) ranging from 21% to 26%. Despite more extensive recrystallization of laminate annealed at 400 °C, thicker intermetallics greatly decreased its strength and plasticity because crack initials and quickly propagates along Mg/Al interface or in the interior of intermetallics.