Deformation mechanism and microstructure evolution during on-line heating rolling of AZ31B Mg thin sheets

An AZ31B sheets were processed by on-line heating rolling (ON-LHR) in five passes. Roll and sheets temperatures were 473 K and 533 K, respectively. The grain size was reduced in the first three roll passes, to a minimum of 4.1 μm, due to dynamic recrystallization, and coarsened in the last two passes due to a combination of dynamic recrystallization and grain growth. The yield strength, ultimate tensile strength and elongation to fracture reached 232 MPa, 347 MPa and 21% in the rolling direction. The maximum yield strength occurred after the fourth pass. The maximum is attributed to the small grain size and the formation of networks of sub-grains and deformed grains. The rolled sheets had a strong basal texture, which was largely unchanged with the number of roll passes. The existence of the strong texture after rolling indicated discontinuous dynamic recrystallization

Enhanced mechanical properties of AZ31B magnesium alloy thin sheets processed by on-line heating rolling

A series of AZ31B magnesium alloy thin sheets were prepared by on-line heating rolling processing at temperatures ranging from 443 K to 623 K with intervals of 60 K to a total thickness reduction of ∼80% from initially 4 mm down to ∼0.8 mm in 7 passes. The experimental results suggest that the fracture elongation value increases rapidly at temperatures below 563 K, and then tends to be stable (563 K-623 K). Whereas the tendency of strength, including yield strength (YS) and ultimate tensile strength, is just an opposite one. Serrated edge in sheets manufactured with low temperatures of 443 K and 503 K. As temperature increases above 563 K, no obvious edge crack can be observed. In addition, YS is sensitive to the grain size at low temperatures while insensitive at higher temperatures, resulting in a significant deviation of the YS from the Hall-Petch (H-P) law. In order to elucidate this deviation, a model of framework is proposed which suggests that the strengthening effects of deformed grains and subgrains are weakened with the increase of the fraction of DRX grains till to losing efficacy when the latter surpasses a certain value, herein about 70%

Microstructure and mechanical behavior of the Mg–Mn–Ce magnesium alloy sheets

The microstructural evolution and mechanical behavior of Mg–Mn–Ce magnesium alloy were investigated in the present study. Mg alloy was prepared with metal model casting method and subsequently hot extruded at 703 K with the reduction ratio of 101:1. The grains were dynamically recrystallized after the extrusion process. Moreover, the (0002) pole figure of Mg–Mn–Ce alloy developed a splitting of pronounced basal texture. The mechanical properties were different due to different angles between c-axis and loading direction (0°, 45° and 90°) in the tensile tests. This significantly induces an asymmetry in the yield behavior. The Mg–Mn–Ce alloy exhibits a classical dimple structure as a result of slip accumulation and ductile tear

Research Progress of As-cast Magnesium Alloys with High Plasticity

It is necessary for cast alloys possessing sufficient plasticity to be subjected to deforming progresses for the improvement of mechanical properties. Developing as-cast magnesium alloys with appreciated plasticity is therefore important to the variety of wrought magnesium alloys and the enlargement of their applications. In this paper, the research progresses of Mg-Al, Mg-Li, Mg-Zn and Mg-RE (rare earth) series magnesium alloys are enclosed, as well as the effects of casting processes. The plasticity enhancement of as-cast magnesium alloys was mainly attributed to the combination of the grain refinement and the second phases introduced by alloying elements, and microalloying with several alloying elements was more favorited. Heat treatment, rapid cooling casting and external electromagnetic field were also beneficial to mechanical properties and worth to be promoted in industrial engineering

The Dynamic Response and Failure Model of Thin Plate Rock Mass under Impact Load

The layered rock mass widely exists in mining, construction, transportation, and water conservancy projects, and the damage phenomena of plate crack and spalling often occurs in the process of coal and rock dynamic disaster in deep mining. Therefore, the rock mass nearby excavation surface is usually considered to be composed of layers of thin plate rock mass to reveal the damage and failure mechanism of rock mass. In the whole dynamic process of mining and coal and rock dynamic disaster, rock mass would bear the dynamic disturbance from mine earthquake, and at present, the mechanical characteristics of rock mass are mainly studied under static load, while dynamic mechanical response characteristics and the mechanisms of dynamic damage, failure, and disaster-causing are still unclear. This study mainly focused on the dynamic response characteristic and failure mechanism of rock mass based on a rectangular thin plate model. The frequency equations and deflection equations of the thin plate rock mass with different boundary conditions (S-F-S-F, S-C-S-C, and C-C-C-C) were established under free vibration by the thin plate model and the dual equation of the Hamilton system, and the deflection equations under impact load were derived based on the Duhamel integral. And then, the effective vibration modes of the thin plate rock mass with different boundary conditions and their natural frequencies were obtained by Newton’s iterative method. Based on the third-strength theory and the numerical simulation results by LS-DYNA, the maximum shear of the effective vibration modes and the processes of damage and failure under impact load were analyzed. The research results showed that the initial position of damage and failure may be determined by effective vibration mode with the lowest frequency; the develop tendency of which by the combined actions of other effective vibration modes and the effective vibration modes with lower frequency could have greater influence on the process of damage and failure of the thin plate rock mass, which are beneficial to revealing the mechanism of coal and rock dynamic disaster

Fusion of Acoustic and Tokenization Features for Speaker Recognition

Abstract. This paper describes our recent efforts in exploring effective discriminative features for speaker recognition. Recent researches have indicated that the appropriate fusion of features is critical to improve the performance of speaker recognition system. In this paper we describe our approaches for the NIST 2006 Speaker Recognition Evaluation. Our system integrated the cepstral GMM modeling, cepstral SVM modeling and tokenization at both phone level and frame level. The experimental results on both NIST 2005 SRE corpus and NIST 2006 SRE corpus are presented. The fused system achieved 8.14 % equal error rate on 1conv4w-1conv4w test condition of the NIST 2006 SRE

Simple Additive-Free Method to Manganese Monoxide Mesocrystals and Their Template Application for the Synthesis of Carbon and Graphitic Hollow Octahedrons

Mesocrystals are of great importance owing to their novel hierarchical microstructures and potential applications. In the present work, a simple additive-free method has been developed for the controllable synthesis of manganese monoxide (MnO) mesocrystals, in which cheap manganese acetate (Mn­(Ac)₂) and ethanol were used as raw materials without involving any other expensive additives such as surfactants, polyelectrolyte, or polymers. The particle size of the resulting MnO mesocrystals is tunable in the range 400–1500 nm by simply altering the concentration of Mn­(Ac)₂ in ethanol. The percentage yield of the octahedral MnO mesocrystals is about 38 wt % with respect to the starting Mn­(Ac)₂. The selective adsorption of oligomers, which was resulted from the polymerization of ethanol, acted as an important role for the mesocrystal formation. A mechanism involving the oriented aggregation of MnO nanoparticle subunits and the subsequent ripening process was proposed. Moreover, for the first time, the as-synthesized MnO mesocrystals were employed as a novel template to fabricate functional materials with an octahedral morphology including MnO@C core/shells, carbon, and graphitic hollow octahedrons. This method shows the importance of mesocrystals not only for the field of material research but also for the application in functional materials synthesis