[en] This paper deals with the TiN coating of a new low alloy high speed steel W3Mo2Cr4VSi. According to transmission electron microscopy and X-ray diffraction investigations, the TiN coating can be divided into two layers: the main-body layer and the transition layer. The main-body layer consists of columnar TiN which is vertical to the substrate surface, with fine-grained TiN and small amounts of ε-Ti₂N between some columns. The transition layer is composed of equiaxed grains of TiN, ε-Ti₂N and α-Fe. The orientation relationship between the columnar TiN and the ε-Ti₂N grains in the main-body layer was found to be (101)_Ti2N parallel (200)_TiN and [111]_Ti2N parallel [011]_TiN. It was shown that the amount of α-Fe in the transition layer decreased with increasing silicon content to this steel. A compressive residual stress between 180 and 200 N mm^-2 exists in the coating. (orig.)

[en] Highlights: • Systematic study of the effect of alloy elements on the magnesium alloy anode’s electrochemical properties. • The effect of Al, Sn, Mn on the electrochemical performance of magnesium alloy anode ranks in the order of Al, Sn and Mn. • Optimized Mg-6Al-1Sn-0.4Mn alloy shows the best electrochemical performance as magnesium anode. The effect of Al, Sn and Mn on the electrochemical properties of extruded magnesium alloy anode was systematically investigated by orthogonal design. The optimal combination, Mg-6Al-1Sn-0.4Mn alloy anode, was obtained through comprehensive analysis. The combination was further verified by the characterization of microstructure, composition and electrochemical performance. The average discharge potential reaches − 1.602 V (vs. SCE), showing obvious discharge superiority against the trial samples. The research result is also of value to the development of low cost, non-toxic and well-performance magnesium alloy anode.

[en] The effects of Sr amount and melt holding time on the grain refinement of AZ31 magnesium alloy treated with a commercial Al-10Sr master alloy are investigated. The effects of solutionizing, rolling, and remelting of commercial Al-10Sr master alloy on the grain refinement of AZ31 magnesium alloy are also investigated. An increase in Sr amount from 0.01 to 0.1 wt.% or melt holding time from 20 to 80 min causes the grain size of AZ31 alloy treated with the commercial Al-10Sr master alloy to gradually decrease. In addition, the solutionizing, rolling, or remelting of commercial Al-10Sr master alloy can improve the refinement efficiency of the master alloy to AZ31 alloy, and the improvement resulting from the remelting is best obvious, followed by rolling and solutionizing, respectively.

[en] Microstructure evolution during homogenization of a low-alloying τ-type Mg-Zn-Al magnesium alloy with a nominal composition of Mg-7% Zn-3% Al was investigated in this paper, using optical microscopy, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry analysis and quantitative image analysis. A anneal treatment following rapid cooling to ambient temperature from homogenization isothermal temperature was adopted to assess the homogenization degree in respect to microchemical distribution. The results show that shorter holding time results in so-called in situ precipitation phenomena, which is attributed to the insufficient diffusion of the element Zn and Al from solute-rich grain boundary region to inner side of grain during homogenization. A homogenization treatment at 325 deg. C for at least 50 h is just enough allowing complete homogenization for such alloy, in point of both morphology and microchemistry of the microstructure, which is deemed to be a key precondition for the optimum combined properties through proper thermal-mechanical treatment

[en] Highlights: • A Mg-Gd-Y-Zn-Mn-Ag alloy with UTS of 533 MPa and elongation-to-failure of 9.0% was produced. • The lamellar LPSO phases prevent the recrystallization process. • Fine dynamic precipitates restrain the growth of recrystallized grains. • The mechanisms of strengthening and toughening of Mg-Gd-Y-Zn-Mn(-Ag) alloys was discussed. - Abstract: The effects of Ag on the microstructure and mechanical properties of a Mg-9Gd-3Y-1Zn-0.8Mn alloy have been investigated. Microstructural analysis indicates that the (Mg,Zn)₃(Gd,Y)-type eutectic phase in the as-cast alloys transform into LPSO phase during solution treatment. The presence of Ag atom facilitates the formation of lamellar LPSO phase in the grain, which restrains recrystallization behavior during extrusion. The formation of β′ and γ′ phases can be remarkably promoted by Ag addition during aging treatment. The co-precipitation of β′ and γ′ phases generates an approximate enclosed microstructure which endows the alloy with ultra-high strength and favorable ductility.

[en] To better understand the influence of alloying elements on the mechanical properties of Mg-X (Al, Sn, Ca, Y, Sc, Er, Gd, and Nd) binary alloys, the local interactions between the solute atoms and basal screw dislocation cores were investigated using first-principles calculations. It is revealed that Rare Earth (Y, Sc, Er, Gd, and Nd) and Ca solute atoms can hinder the dissociation behavior of the full basal dislocation core to different extents. Moreover, Y, Sc, and Er tend to stabilize the perfect Burgers vector of basal dislocations. Furthermore, Sn, Y, and Nd were selected to access the interactions between solute atoms and partial dislocations. It is found that Y and Nd can alter the structure of partial dislocation and reduce the width of the stacking fault at specific locations. By comparison, Al and Sn solutes slightly influence the width of the stacking fault. The energies of relaxed basal dislocation cores decorated by Rare Earth and Ca are significantly lower than those decorated by Al and Sn, which suggests that a stronger binding is present between Rare Earth elements, Ca solute atoms, and basal dislocation cores. Moreover, non-planar basal dislocation cores would be induced by Rare Earth solutes. Finally, the physical factors of alloying elements influencing dislocation core structures and the implications of the diverse geometries of dislocation cores to mechanical properties of Mg alloys are discussed.

[en] To investigate the mechanical behavior of AZ61 alloy in a mushy state, uniaxial tensile tests of as-extruded AZ61 alloy have been implemented at temperatures of 475–575 °C at a strain rate of 3 s⁻¹. Experimental results show that zero strength and zero ductility emerged at 575 and 525 °C, respectively. Abnormal coarse grains with sugar-like morphology and molten Mg₁₇Al₁₂ phases were observed in the brittle temperature range. The grain boundaries and surface were gradually covered partially or completely by a liquefied microstructure as temperatures increased. Small micropores developed into short cracks at temperatures above 525 °C and then to large cracks throughout the grain boundaries at 575 °C. It is therefore suggested that crack propagation was controlled by the quantity and distribution of molten phase in the mushy zone. Three types of interfacial wedge cracks are applied to explicate the fracture behavior of the alloy at elevated temperatures.

[en] One of the major concerns during gas tungsten arc (GTA) welding of cast magnesium alloys is the presence of large macroporosity in weldments, normally thought to occur from the presence of gas in the castings. In this study, a double-sided GTA welding process was adopted to join wrought magnesium AZ91D alloy plates. Micropores were formed in the weld zone of the first side that was welded, due to precipitation of H₂ as the mushy zone freezes. When the reverse side was welded, the heat generated caused the mushy zone in the initial weld to reform. The micropores in the initial weld then coalesced and expanded to form macropores by means of gas expansion through small holes that are present at the grain boundaries in the partially melted zone. Macropores in the partially melted zone increase with increased heat input, so that when a filler metal is used the macropores are smaller in number and in size

[en] The crystalline microstructure, surface morphology and dielectric properties of BaZr_0.2Ti_0.8O₃ (BZT) ceramics were investigated. The c-axis lattice parameter (c=0.4107nm) of the BZT ceramics is larger than the a-axis one (a=0.4101nm). It was found that the crystal structure of the ceramics is to be tetragonal phase, and close to cubic phase. The temperature dependence of the relative permittivity showed that BaZr_0.2Ti_0.8O₃ ceramics is to be relaxor ferroelectrics with the diffuseness constant equal to 1.93. As the applied maximum voltage increased from 500V to 1000V and 1500V, the remanent polarization increased from 1.69μC/cm² to 3.10μC/cm² and 3.60μC/cm², furthermore the coercive field increased from 0.88kV/cm to 1.19kV/cm and 1.35kV/cm.

[en] Microstructure and electromagnetic interference shielding properties of extruded Mg-Zn-Ce-Y-Zr alloys were systematically investigated. A bimodal grain structure of fine recrystallized grains and deformed grains was observed in the alloys. Yttrium (Y) and cerium (Ce) refined the recrystallized grains. Mg-Zn-Ce phase, Mg₃Zn₃Y₂ phase and a few precipitates containing Zn and Zr were observed. Y and Ce additions changed the texture of the alloys. When the total rare earth content reached 4 wt.%, the texture was remarkably weaker than other studied alloys. The shielding capacity increased first and then decreased with Y contents. The value of shielding effectiveness for the extruded Mg-5Zn-1Ce-2Y-0.6Zr alloys reached 79-118 dB in the frequency range of 30 MHz-1.5 GHz, which was significantly higher than that of some aluminum alloys. The addition of Y and Ce is effective in improving the shielding capacity in Mg alloys. The electrical conductivity and second phases in the alloys were important in enhancing shielding effectiveness. The texture and precipitation exerted significant effect on electrical conductivity. In addition, subsequently aging treatment evidently improved shielding effectiveness.