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In order to tackle the environmental problems induced by Portland cement production and industrial solid wastes landfilling, this study aims to develop novel ternary cementless fly ash-based geopolymer by recycling red mud and blast furnace slag industrial solid wastes. The fresh-state properties, mechanical strength, water permeability, phase assemblage and microstructure were systematically investigated to evaluate the performance variation and reveal the hydration mechanism for geopolymers with different mixing proportions. The results showed that a higher slag content or a lower red mud content could result in the higher fluidity and shorter setting time for fresh mixture. The existence of slag promoted the transformation of N-A-S-H to C-A-S-H gel, which contributed to higher compressive strength and better resistance to water penetration. However, an excessive incorporation of 30% red mud may impede the generation of N-A-S-H gel and form more flocculent-like loose hydrates, thus to mildly degrade the mechanical strength and anti-permeability. The synergetic utilization of red much and blast furnace slag in fly ash-based geopolymer led to much less CO 2 emission compared with the condition that red much or slag was singly added, which demonstrated prominent environmental advantages for such kind of ternary cementless geopolymer with equivalent mechanical strength. [Display omitted] • A series of novel cementless geopolymers with ternary solid wastes were designed with low CO 2 emission. • Synergetic utilization of red mud and slag endowed fly ash-based geopolymer with adaptive fresh properties. • The influential mechanisms of red mud and slag on strength and permeability of geopolymer were clarified. • The hydration products and microstructure of geopolymer with red mud and slag were revealed. [ABSTRACT FROM AUTHOR]

A Mg-Gd-Nd-Zn-Zr alloy was processed by equal channel angular pressing (ECAP) at 375 °C. The grain size of Mg-Gd-Nd-Zn-Zr alloy was refined to ~ 2.5 μm with the spherical precipitates (β 1 phase) distributing in the matrix. The mechanical properties of ECAPed alloy were significantly improved as a result of the grain refinement and precipitation strengthening. The corrosion rate of the ECAPed magnesium alloy in simulated body fluid dramatically decreased from 0.236 mm/a to 0.126 mm/a due to the strong basal texture and refined microstructure. This wrought magnesium alloy shows potentials in biomedical application. [ABSTRACT FROM AUTHOR]

A cast Mg–2.9Gd–1.5Nd–0.3Zn–0.3Zr alloy was processed by equal channel angular pressing at 375 °C for 1, 4 and 8 passes. Microstructure, texture and mechanical properties were investigated. The results indicate that the average grain size decreases from ∼50 μm at as-cast state to 1.23 μm during 8-pass ECAP. Homogeneity of microstructure improved obviously and new spherical β 1 phase gradually precipitated from α-matrix with the increase of pass. Moreover, the random texture was converted to the strong (0002) basal texture. The ultimate tensile strength (UTS), yield strength (YS) and elongation increased in all passes, and the magnesium alloy obtained the excellent mechanical property at ECAP for 8 pass, for which the UTS, YS and elongation reached to 274.1 MPa, 231.6 MPa and 20.3%, respectively. The increase in strength and ductility was owing to cooperative effects of grain refinement, precipitation strengthening and texture evolution. [ABSTRACT FROM AUTHOR]

The differences in microstructural characteristics, mechanical properties, and corrosion behavior of the as-cast and solution-treated Mg-xGd-1.5Nd-0.5Zn-0.5Zr alloys (Mg-xGd, x = 1, 3, and 5) were studied and discussed. The as-cast Mg-xGd alloys mainly consisted of an α-Mg and island-like eutectic (Mg,Zn)3RE phase, a few cuboidal phases (REH2), and a ZnZr phase. With the increase of Gd content, the grain sizes of the as-cast Mg-xGd alloys decreased. Compared to the microstructure of the as-cast Mg-xGd alloys, the eutectic (Mg,Zn)3RE phase disappeared and the cuboidal REH2 phases existed in the solution-treated Mg-xGd alloys. A large amount of ZnZrx phase was precipitated from α-Mg in the Mg-3Gd alloy and demonstrates a flower-like distribution. The ultimate tensile strength (UTS) and yield strength (YS) of the solution-treated Mg-xGd alloys increased with an increasing Gd content, with the UTS and YS of the Mg-5Gd alloys reaching 217.5 and 125.2 MPa, respectively. Immersion and electrochemical tests showed that the as-cast Mg-3Gd alloy presented the best corrosion resistance with a corrosion rate of 0.285 mm/yr. The corrosion resistance of the solution-treated Mg-3Gd alloy attained the lowest value (0.973 mm/yr), due to the large quantities of ZnZrx with a flower-like phase distribution, forming series of galvanic couple groups with the α-Mg. [ABSTRACT FROM AUTHOR]

• Trailing ultrasonic assisted laser welding (T-ULW) is proposed to weld 0.6 mm thick stainless steels sheet. • The theoretical model of ultrasonic assisted laser welding is established. • The welding temperature fields in (T-ULW) and LW are numerically simulated. • T-ULW helps to refine the grain of weld and enhance the mechanical properties of welded joint. Ultrasonic assisted laser welding (ULW) is a newly developed welding method. In this paper, a new kind of ultrasonic assisted laser welding method, which is named trailing ultrasonic assisted laser welding (T-ULW) is proposed. First, the welding temperature fields as well as the weld pool temperature evolution in trailing ultrasonic assisted laser welding (T-ULW) and conventional laser welding (LW) are numerically simulated, and the shapes of the molten pools during T-ULW and LW are observed by a high-speed camera monitoring system. Both the simulation and monitoring results show that ultrasonic can reduce the temperature gradient of the weld pool and prolong the solidification time. Then, such three kinds of welding methods as T-ULW, common fixed-position ultrasonic assisted laser welding (F-ULW) and LW are used to weld SUS301 stainless steel sheet with a thickness of 0.6 mm respectively, and their performances are comparatively investigated by analyzing the experimentally-obtained macro morphologies, microstructures of welded joints. Macro morphology analysis results show that ultrasonic vibration not only elongates the molten pool, but also changes the cross-sectional shapes of the welds in such a way that decreases the top width and increases the bottom width. Microstructure analysis results indicate that the fusion zone of the welds obtained by T-ULW is uniformly distributed mainly by the refined equiaxed grains. Subsequently, the crystal refinement mechanisms of the welds in ultrasonic-assisted laser welds of SUS301 stainless steel are theoretically analyzed and experimentally verified, which show that due to ultrasonic disturbance, the temperature gradient of the molten pool is decreased, a stress field is generated in the welds and a so-called ultrasonic cavitation effect is produced in the molten pool. Such three mechanisms play very important roles in refining crystals in different ways that the decreased temperature gradient provides a good nucleation condition for the growth of equiaxed dendrite, and both the generated stress and ultrasonic cavitation cause the grain boundary to fracture, thereby form more new grain boundary, which finally lead to form fine and uniform grains in the welds. Finally, the mechanical properties of the joints are measured, and the results demonstrated that ultrasonic assisted laser welding especially T-ULW enables not only to increase the tensile strength of the welds, but also to improve the ductility of the welds. [ABSTRACT FROM AUTHOR]

Homogenization treatment and equal channel angular pressing was applied to Mg–Y–Nd–Zr alloy cast ingot. Uniform grains with a grain size of ~1.5 μm and spherical secondary-phase preferentially located at the grain boundaries were obtained. Excellent high-strain rate superplasticity of 860% and 960% was achieved at 500 °C, 1×10 −1 s −1 and 475 °C, 2×10 −2 s −1 , respectively, for the first time such a high-strain rate superplasticity was achieved in magnesium alloys processed by ECAP. The maximum elongation of 1120% was achieved at 475 °C, 3×10 −3 s −1 . They were attributed to the thermal stability of uniform fine-grain microstructure and the coordination function of secondary-phase. [ABSTRACT FROM AUTHOR]