Multi-walled carbon nanotubes (MWCNTs) reinforced hollow glass microspheres (HGMs)/epoxy syntactic foam was fabricated. The effects of ultrasonication on the density, compression strength, and water absorption properties were studied. Better dispersed MWCNTs can be obtained after ultrasonication treatment, but an increasing viscosity will lead to a larger amount of voids during syntactic foam preparation especially when the content of HGMs is more than 70 vol%. The existing voids will decrease the density of epoxy syntactic foam. However, the ultrasonication does not change the compression strength much. Ultrasonication treatment will decrease the water absorption content due to the better dispersion and hydrophobic properties of MWCNTs. But a significant increase of water absorption content occurs when HGMs is more than 70 vol%, which is attributed to the higher viscosity and larger amount of voids.

The microstructure and mechanical properties of AZ80 magnesium alloys with varying Nd, Gd contents were investigated. The results revealed that the as-cast microstructure of AZ80 alloy was composed of α-Mg matrix and divorced eutectic β-Mg17Al12 phases. The fraction of Mg17Al12 phase was reduced when 0.6 wt.% Nd was added, and new rod-shaped Al11Nd3 phase and small block-shaped Al-Nd-Mn phase appeared. With Gd addition, the Gd elements mixed with Nd to form rare earth phases. New block-shaped Al2Gd and Al2Nd phases which were collectively called Al2RE phases were observed in the microstructure with more than 0.6 wt.% Gd addition. Moreover, the addition of Gd could promote the precipitation of block-shaped Al2RE phase, and inhibit the original rod-shaped Al11Nd3 phase. The AZ80-0.6Nd-0.6Gd alloy exhibited the optimal mechanical properties among all the experimental alloys, in which the tensile strength, yield strength and elongation were 215, 145 MPa and 8.33%, respectively.The as-cast microstructure of AZ80 alloy is composed of α-Mg matrix and divorced eutectic β-Mg17Al12 phases. The fraction of Mg17Al12 phase is reduced when 0.6 wt.% Nd is added, and new rod-shaped Al11Nd3 phase and small block-shaped Al-Nd-Mn phase appear. The addition of Gd in the Nd modified alloy could promote the precipitation of block-shaped Al2RE phase, and inhibit the original rod-shaped Al11Nd3 phaseSEM image of as-cast experimental alloys(a) AZ80; (b) AZ80-0.6Nd; (c) AZ80-0.6Nd-0.3Gd; (d) AZ80-0.6Nd-0.6Gd; (e) AZ80-0.6Nd-0.9Gd; (f) AZ80-0.6Nd-1.2GdFigure optionsDownload full-size imageDownload as PowerPoint slide

Cu90Zr10-xAlx (x=1, 3, 5, 7, 9; at.%) alloy rods were synthesized based on rapid solidification method. The structure, distribution of elements, mechanical properties and electrical conductivity of the Cu-based alloy samples were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), electro-probe micro-analyzer (EPMA), uniaxial compression test and four-probe technique. The as-cast Cu90Zr10-xAlx (x=1, 3, 5; at.%) alloy rods with a diameter of 2 mm exhibit good mechanical properties and electrical conductivity, i.e., high compressive yield strength of 812-1513 MPa, Young’s modulus of 52-85 GPa, Vickers hardness of 250-420 and electrical conductivity of 11.1%-12.6% IACS (International Annealed Copper Standard). The composite microstructure composed of high density fibrous duplex structure (Cu5Zr and α-Cu phases) is thought to be the origin of the high strength.

The effect of spiral magnetic field (SMF) on the solidification process of Sn-20 wt.%Pb hypoeutectic alloy was studied in this work. The temperature distribution and the macrosegregation together with the eutectic lamellar spacing during solidification were measured under different magnetic fields. The results indicate that the compositions in the top and bottom portions of the sample are nearly the same and the segregation phenomenon is basically eliminated by SMF at an exciting current of 125 A. The morphology of the primary phase transforms from coarse dendrite to rosette or ellipsoidal equiaxed crystal and the spacing of the eutectic lamellar increases from 1.6 to 3.9 µm when the exciting current increases from 0 to 125 A. Moreover, if the exciting current is high enough, the forced fluid flow caused by SMF will enhance the process of transition from lamellar eutectic structure to anomalous rod-like one.

Microstructures and mechanical properties of the Mg–8Gd–5Y–2Zn–0.5Zr–xNd (x=0, 0.5, 1 and 2 wt%) alloys in the as-cast, solid solution and as-aged conditions have been investigated. The experimental results reveal that Nd can impede the formation of LPSO phases during the solidification process and suppress the transformation of Mg5(Gd, Y, Zn) to LPSO phase at high temperature heat-treatment. Addition of 2% Nd leads to the disappearance of the LPSO phases in the as-cast alloy. After heat-treatment at 520 °C for 16 h, the uniform LPSO phases, which are transformed from Mg5(Gd, Y, Zn) phases and refined by the Nd, result in a higher solid solubility and greater aging effect. With increasing Nd content, the residual Nd-rich Mg5(Gd, Y, Zn) phases in the solid solution alloys gradually increase and produce an adverse effect on the mechanical properties. The alloy with the addition of 0.5% Nd shows the optimal mechanical properties in the as-aged alloys, and its ultimate tensile strength, yield strength and elongation are 308 MPa, 252 MPa and 5.3%, respectively.

Three kinds of alloys Al–Zn–Mg–Cu–Zr, A1–Zn–Mg–Cu–Zr–Gd and A1–Zn–Mg–Cu–Zr–Gd–Y were prepared by cast metallurgy. The effects of Gd and Y additions on the microstructure and properties of Al–Zr–Mg–Cu–Zr alloys were investigated by optical microscopy (OM), tensile test, scanning electron microscopy (SEM), electronic probe microanalysis (EPMA) and transmission electronic microscopy (TEM). The results show that the combined additions of Gd and Y to the A1–Zn–Mg–Cu–Zr alloys effectively retard the mergence and growth of the sub-grain during the recovery process, significantly inhibit the recrystallization of Al matrix. σb, σ0.2 and δ are improved with increasing Gd and Y content, and the improving amplitudes reach 11.49%, 14.61%, 63.11% respectively and have better relative intracrystalline solubility.Highlights► The inhibition recrystallization effect is more obvious when adding complex Gd and Y. ► The micro-segregation of the Al–Zn–Mg–Cu–Zr alloy could be significantly reduced after adding Gd or both with Gd and Y. ► Adding single Gd or composite Gd and Y can both can accelerate the peak aging time, improve the peak hardness, and extend the duration of peak aging time. ► Compared with Al–Zn–Mg–Cu–Zr alloy, the alloys with Gd or with Gd and Y can significantly improve the strength and elongation of T6 state.

Continuous casting method for massive production of steel, aluminum, copper or other crystalline alloy ingot is a very important industrial technology for its low energy consumption and high productivity. In this study, a new continuous casting method was developed for the massive production of bulk metallic glass ingot with centimeter-scale diameter without length limitation. An intermittent withdrawal procedure was practiced for continuous casting of bulk glassy alloy. The new developed continuous casting method can provide a cooling speed as high as that provided by the stationary mold casting method. A Zr-based glassy alloy rod with a diameter of about 10 mm and length of tens of centimeters was prepared by the continuous casting method for the first time.Research Highlights►We proposed a new continuous casting method for preparation of bulk metallic glass. ►We produced bulk metallic glass long rod with a diameter of 10 mm. ►An intermittent withdrawal procedure is practiced for the continuous casting. ►The rapid solidification process of the glassy alloy was actually subjected.

The tensile properties, electrical conductivity, and microstructure of the forged Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy were investigated after a two-step ageing treatment at 120 and 170°C. The results indicate that the strength of the alloy reaches the peak value at 170°C for 1 h during the second step ageing and then decreases sharply. However, the electrical conductivity value increases continuously with the second ageing time increasing. The fracture mechanism of the alloy is intergranular fracture for 1 h and then changes to dimple transgranular fracture later, and the toughness of the alloy is improved significantly. The phases of η′ and η are major precipitates in the alloy under the two-step ageing condition. Discontinuous grain boundary precipitates and precipitate-free zones along the grain boundary are clearly observed.

Al-4.0Cu-1.4Mg-0.6Mn (2E12) and Al-4.0Cu-1.4Mg-0.6Mn-0.3Zr aluminum billets were manufactured by soft-contact electromagnetic continuous casting (EMC). Subsequent forging and heat treatment were conducted and the effects of Zr on the microstructure and properties of the Al-4.0Cu-1.4Mg-0.6Mn alloy were studied. The results show that the addition of 0.3% Zr can reduce the dendrite and refine grains. During forging and solution treatment, fine and dispersive Al3Zr particles precipitated from the supersaturated α (Al) solid solution in the heating process of the billet can effectively pin dislocations and subgrain boundaries. Because of the addition of Zr, the mechanical properties are improved with the tensile strength, yield strength, elongation, and contraction of the area increasing by 5.4%, 11.3%, 9.7%, and 12.6%, respectively. Moreover, under the condition of R = 0.1, the fatigue crack growth rate (da/dN) of the Al-4.0Cu-1.4Mg-0.6Mn-0.3Zr alloy is lower than that of the Al-4.0Cu-1.4Mg-0.6Mn alloy.