Selective laser melting (SLM) technology has been used to manufacture the AZ91D magnesium alloy. The relative density, microstructure, microhardness and tensile properties of the deposited AZ91D samples at different laser energy inputs were characterized. The results indicate that laser energy input plays a significant role in determining formation qualities of the SLMed samples. High density samples without obvious macro-defects can be obtained between 83 J/mm 3 and 167 J/mm 3 . The SLMed AZ91D presents a unique layerwise feature in which the fully divorced eutectic β-Mg 17 Al 12 distributing along the boundary of the equiaxed α-Mg matrix. The average size of α-Mg in overlapping regions is a little larger than that in the center of the scanning tracks due to the remelting process though the element distributions of Mg and Al are quite uniform. The microhardness of all samples shows directional independence. The microhardness and tensile strengths of the SLMed AZ91D at room temperature are superior to those of the die-cast AZ91D due to the combined effect of grain refinement and solid solution strengthening.

Effect of energy input on formability, microstructure and mechanical properties of selective laser melted AZ91D magnesium alloy

Crystal plasticity analysis of texture development in magnesium alloy during extrusion

Experimental investigations on the synthesis of W–Cu nanocomposite through spark plasma sintering

Tungsten copper (W-Cu) composites, as a traditional refractory material, are promising materials for manufacture of electrical contacts and electrodes, heavy duty electronic contacts, welding and electro-forging dies, heat sinks, packaging material, arcing resistance electrodes and thermal management devices owing to their excellent properties. This critical review presents and discusses the current progress of W-Cu composites. Starting with an introduction of the synthesis methods for W-Cu composites, including the conventional and modern preparation approaches. After that we focus on the description of the improvement of mechanical properties and arc-erosion properties by modification techniques. Finally, the advantages of W-Cu composites in applications such as electrical contacts, electronic packaging materials, and heat sinks, as well as military materials, are described, respectively.

Recent progress in development of tungsten-copper composites: Fabrication, modification and applications

ZK60 magnesium alloy sheets with various texture states were successfully fabricated by controlling the rolling temperature in multi-pass lowered-temperature rolling. The microstructure including texture and the mechanical properties of the resulting sheets were investigated. Results showed that dynamic recrystallization (DRX) during current rolling process could be realized at lower deformation temperature when the thickness reduction per pass was larger than 30%, and with its help, the grain size was significantly refined and the microstructure homogeneity strikingly improved. In this circumstance, deformation temperature mainly influenced the texture state of the resulting sheets, implying that with the increase of deformation temperature the distribution of (0002) basal planes remained stable along the rolling direction but gradually increased along the transverse direction. The calculation results about the friction stress for various deformation modes indicated that the changing ratios of the critical resolved shear stress (CRSS) for the non-basal slip to that for basal slip resulted in this texture difference. Additionally, for the samples with the dominant deformation mode of basal slip, the yield stress gradually decreased and the uniform elongation increased with the weakening of basal texture. However, if dominant deformation mode changed, an abrupt change would occur in their values. This change of yield stress came from the change of CRSS, while uniform elongation from strain hardening rate.

Effect of deformation temperature on texture and mechanical properties of ZK60 magnesium alloy sheet rolled by multi-pass lowered-temperature rolling

A feasible method combining extrusion, rolling and annealing was designed to fabricate magnesium alloy sheets with various texture patterns and grain sizes Tensile tests at ambient temperature revealed that grain refinement and texture together contributed to the great differences of the presentative Hall–Petch parameters during different rolling stages With texture variation, competition between slip and twinning during yield behavior leads to two conspicuous Hall–Petch relations It was found that slip-dominated Hall–Petch relation exhibited a much larger frictional stress of about 142 MPa and a texture dependent slope ranging from 121 to 225 MPa μm 1/2  Comparatively, twinning-induced Hall–Petch relation exhibited a much lower frictional stress of about 25 MPa and a higher but unchanged slope of about 300 MPa μm 1/2 , meaning that the parameters are primarily controlled by the stress to activate twinning

Yield strength behavior for rolled magnesium alloy sheets with texture variation

Hot rolling of ZK61 Mg alloy sheets with homogeneous structure was performed at the temperature range of 553–433 K to examine the influence of rolling temperature on the microstructure refinement and uniformity. As the rolling temperature decreased, the microstructure was refined continuously with the decrease of Zener–Hollomon parameter via dynamic recrystallization. Detailed investigation of the microstructures revealed that dynamic recrystallization was completed at the temperature above 503 K, and partially from 493 K to 453 K, but did not occur below 443 K. Weighted by their uniformity, the temperature range of 523–493 K can be considered to be the optimum temperature values for hot rolling. Under this condition a uniform structure with a grain size of about 3.0 μm was obtained, and a comprehensive mechanical performance was achieved with tensile strength of 330 MPa, yield strength of 240 MPa and elongation of 24%. In addition, the relations between microstructure and mechanical properties were also analyzed.

Optimization of rolling temperature for ZK61 alloy sheets via microstructure uniformity analysis

The extrusion process of AZ31 magnesium alloy has been simulated. First, a series of tests were designed to obtain the simulation parameters: stress–strain curves, friction factors and heat transfer coefficient. Then, a special extrusion process was carried out and simulated by DEFORM-2D simultaneously. The results reveal that the simulated temperature–time curve agrees well with the measured one, indicating the good accuracy of the simulation parameters. Accordingly, the extrusion of AZ31 at different conditions was analyzed in detail. The extrusion loads and temperature distribution of billets were obtained.

Simulation of extrusion process of AZ31 magnesium alloy

High temperature deformation behaviors of the unhydrogenated and hydrogenated Ti-46Al-2V-1Cr-0.3Ni (at%) alloys were investigated in the temperature range 1050–1200 °C and strain rate range 0.001–1 s−1. The flow stress of the hydrogenated alloy was lower than that of the unhydrogenated alloy, which was mainly attributed to hydrogen-promoted lamellar decomposition, twinning and dynamic recrystallization. Processing maps of the unhydrogenated and hydrogenated alloys were constructed. The stability domain of the hydrogenated alloy was enlarged in comparison with that of the unhydrogenated alloy, meaning hydrogen enhanced the hot workability of the Ti-46Al-2V-1Cr-0.3Ni alloy. Hydrogen activated slip systems so that lamellar bending more easily occurred in the hydrogenated alloy, which made inter-lamellar fracture convert into trans-lamellar fracture. Therefore, crack propagation was restrained in the hydrogenated alloy during hot deformation. The critical strain of the hydrogenated alloy was less than those of the unhydrogenated alloy, meaning the dynamic recrystallization occurred earlier in the hydrogenated alloy. γ-phase discontinuous dynamic recrystallization was promoted due to hydrogen addition, leading to a consumption of plentiful dislocations, which restrained continuous dynamic recrystallization to some extent. Hydrogen-promoted discontinuous dynamic recrystallization was mainly attributed to hydrogen-promoted lamellar decomposition, twinning, and hydrogen-decreased stacking fault energy.

Positive influence of hydrogen on the hot workability and dynamic recrystallization of a γ-TiAl based alloy

In this paper, a new way to make W–40 wt.%Cu composites by liquid sintering and hot-hydrostatic extrusion has been put forward, and using this method, the billets with fully densification, fine microstructure, and good properties have been successfully obtained. The experimental results show that, the relative density of cold-pressed compact is above 70%, and after liquid sintering, the relative density of the billet can be increased to 98% at the most. Then after hot-hydrostatic extrusion the relative density is up to 99.8% eventually. The specific conductance of the so-fabricated W–40 wt.%Cu composite can reaches 56%IACS after extrusion, and the Vickers-hardness reaches 144 HV.

Z.Y. Liu

Papers

Yield strength behavior for rolled magnesium alloy sheets with texture variation

Optimization of rolling temperature for ZK61 alloy sheets via microstructure uniformity analysis

Simulation of extrusion process of AZ31 magnesium alloy

Positive influence of hydrogen on the hot workability and dynamic recrystallization of a γ-TiAl based alloy

Research on the densification of W–40 wt.%Cu by liquid sintering and hot-hydrostatic extrusion