Zhuoliang Li

Bio: Zhuoliang Li is an academic researcher from Northeastern University (China). The author has contributed to research in topics: Necking & Strain rate. The author has an hindex of 1, co-authored 1 publications receiving 22 citations.

Superplasticity, flow and fracture mechanism in an Al–12.7Si–0.7Mg alloy

Abstract: The superplastic behavior of an Al–12.7mass%Si–0.7mass%Mg alloy was investigated under different conditions. Reasonable superplastic elongations were achieved in the fine-grained (9.1 μm) Al–Si–Mg alloy at temperatures ranging from 733 to 793 K at initial strain rates ranging from 1.67×10 –4 to 1.67×10 –3 s −1 . A maximum elongation to failure of 379% was demonstrated with a strain rate sensitivity, m , of 0.52 and an activation energy for flow, Q , of 156.7 KJ/mol at 793 K at an initial strain rate of 1.67×10 –4 s −1 , which is close to the lattice diffusion activation energy of aluminum. The dislocation activity within Al grains indicated that intragranular slip is the accommodation mechanism of grain boundary sliding. EBSD (Electron Backscatter Diffraction) results revealed that most grain boundaries were high angle boundaries and therefore indicated that boundary sliding and grain rotation occurred during deformation. A deformation mechanism map was plotted for the Al–Si–Mg alloy at 793 K and it is shown that the experimental datum points are in excellent agreement with the predictions of the map. Most cavities were formed around silicon particles and the cavity formation mechanism was proposed. The observation on the fracture surface revealed the presence of filaments. The filament quantity or density increased with increasing testing temperature, which can be interpreted by the transition of dislocation viscous glide creep to grain boundary sliding mechanism at elevated temperatures. The formation of filaments was related to the deformation mechanisms and the lattice diffusion at elevated temperatures. The superplastic fracture in the Al–Si–Mg alloy exhibited a diffuse necking and was a pseudo-brittle fracture. The fracture mechanism was intergranular fracture.

Superplasticity of a dual-phase-dominated Mg-Li-Al-Zn-Sr alloy processed by multidirectional forging and rolling

Abstract: The microstructures, mechanical properties, deformation mechanism and cavitation growth of Mg-10.2Li-2.1Al-2.23Zn-0.2Sr alloy subjected to multidirectional forging and rolling (MDFR) were studied to examine the deformability of the Mg-Li alloy. X-ray diffraction (XRD) results confirm the existence of α (Mg) and β (Li) phases and Mg17Al12, Al4Sr and LiMgAl2 intermetallic compounds. Studies of the microstructures reveal that a thin banded-grained microstructure with a grain size less than 3.75 µm is obtained via MDFR and annealing at 523 K for 1 h. There were significant grain refinements. The maximum elongation to failure was 712.1%, and this was obtained in the current alloy at 623 K with a strain rate of 1.67 × 10−3 s−1. The strain rate sensitivity exponent and the activation energy for deformation were estimated to be 0.884 and 91.9 kJ/mol, respectively. This indicates that the rate-controlling deformation mechanism under the aforementioned condition is grain boundary sliding controlled by lattice diffusion. Experimental cavity observations show the existence of cavity interlinkage or stringers. A new plasticity-controlled cavity growth rate equation considering cavity interlinkage was established, and a cavity growth diagram was constructed. The diagram prediction is consistent with the experimental results. In addition, fractographs show that the intergranular fracture is a ductile fracture mechanism. At room temperature, the ultimate tensile strength of 242 MPa and the elongation of 23.59% were obtained in the present alloy.

Effects of stress concentration on low-temperature fracture behavior of A356 alloy

Abstract: The effect of stress concentration on the dislocation motion, the Si particles and the crack propagation path in A356 alloy at the temperature of 20 °C to −60 °C was analyzed by scanning electron microscope and optical microscope using a series of notched tensile specimens and normal tensile specimens. The results show that the sensitivity of A356 alloy to the stress concentration increases, the tensile strength and yield strength of normal specimens and notched specimens increase, and the elongation shows a decreasing trend with the decrease of test temperature from 20 °C to −60 °C. The yield strength is not affected by the notch, and the tensile strength is sensitive to the stress concentration. Stress concentration leads to a large number of dislocation generation. Local plastic deformation occurred in the stress concentration region during the tensile process firstly. With the stress concentration in the aluminum matrix between the Si phase and the crack further increasing, the distribution of cracks along the Si phase leads to the cracking of aluminum matrix particle.

Achieving high superplasticity of a new Al–Mg–Sc–Zr alloy sheet prepared by a simple thermal–mechanical process

Abstract: A new fine-grained Al–Mg–Sc–Zr alloy sheet with the grain size of 2.5 μm was prepared by simple rolling and thermal treatment process. Superplastic investigations in the temperature range of 450–550 °C and initial strain rate range of 1×10−3 s−1–1×10−1 s−1 show that a maximum elongation of 3250% is achieved at 525 °C and 5×10−3 s−1. The alloy also exhibits excellent superplastic ductility (>2390%) in the temperature interval 475–500 °C at 5×10−2 s−1. Analyses on the superplastic data reveal that the average values of the strain rate sensitivity and activation energy of the Al–Mg–Sc–Zr alloy are about 0.45 and 83 KJ/mol, respectively. The microstructure results show that the studied alloy is characterized by a high fraction of low angle grain boundaries and strong Copper, Brass and Cube texture. During superplastic deformation, low angle grain boundaries gradually transfer into high angle grain boundaries and the grains gradually orientate randomly. The fine coherent Al3(Sc, Zr) particles play an important role in obtaining excellent superplasticity. Grain boundary sliding is the predominant deformation mechanism.

Characterization of a novel 14H-LPSO structure and related elevated-temperature mechanical behaviors in an extruded Mg–Y–Zn–Cu alloy

Abstract: A Mg-2.1Y-0.5Zn-0.6Cu-0.1Zr (WZC200, in at. %) alloy was developed and conducted to extrusion process to refine the grains as well as LPSO structure, aiming to investigate the mechanical behaviors at ambient and elevated temperatures and their relations with microstructures. A 14H-LPSO structure with stacking sequence of ABCBCACACACBCBA, consisting of twin-related building blocks with a novel CBCA-type, was revealed in the solution-treated WZC200 alloy. Fully recrystallized microstructure with grain size of ⁓14 μm, refined LPSO structure and weaken texture were obtained through extrusion process. The tension results tested at ambient and elevated temperatures revealed ultimate tensile strength (UTS) of 317 MPa along with excellent elongation-to-failure of 26.5% at RT, moderate UTS above 275 MPa with occurrence of serrated flow in the tensile curves in the range 150–200 °C, and obviously declined UTS (⁓150 MPa) along with superplastisity of 155% at 300 °C. The observed serrated flow in the range 150–200 °C was mainly attributed to the dynamic strain ageing. The dramatic drop in UTS at 300 °C was ascribed to fragmenting of LPSO phases and probably significant activation of non-basal slips, these two factors help to coordinate deformation between LPSO and the matrix and restrain the cavity nucleation, resultantly contributing to the observed superplasticity at this temperature.