Li Ping Wang

Spheroidal microstructure formation and thixoforming of AM60B magnesium alloy prepared by SIMA process

The microstructure development in the semi-solid state of AM60B magnesium alloy prepared by strain induced melt activation (SIMA) was described. In the SIMA route, cyclic extrusion compression (CEC) and conventional compression were used to predeform as-cast AM60B, respectively. Partial remelting and thixoforming were also carried out within the semi-solid zone. The results showed that coarse-grained structure disappeared and a fine-grained structure resulted in the CEC formed alloy. However, coarse grains and recrystallized grains co-existed in the compression formed alloy. During partial remelting, the alloy treated by CEC exhibited ideal, fine microstructure, in which completely spheroidized grains contain little entrapped liquid. Polygonal grains were spheroidized to some extent but the previous irregular shape was still obvious in the compression formed alloy. The mechanical properties of the thixoformed AM60B produced by CEC plus partial remelting were better than those of the thixoformed alloy produced by compression plus partial remelting.

Tensile properties of ZnO- and ZnAl2O4-coated aluminum borate whiskers reinforced aluminum composites at elevated temperatures

ZnO- and ZnAl2O4-coated aluminum borate whiskers reinforced pure aluminum composites were fabricated by squeeze casting. The tensile properties of the composites at elevated temperatures were tested. The results indicate that the maximum tensile stress of the composite decreases with the increase of tensile temperature; however, the tensile strain of the composite initially increases and later declines. ZnO, especially, ZnAl2O4 coating of the whiskers can effectively improve the ultimate tensile strength of the composite at elevated temperatures. On the basis of fractographic analysis, the fracture mechanisms of the composites at elevated temperatures were also investigated.

Microstructure in the semi-solid state and mechanical properties of AZ80 magnesium alloy reheated from the as-cast and extruded states

The multi-axial forging (MAF) process was introduced into the strain induced metal activation (SIMA) process to replace conventional forging. Microstructure evolution of MAF formed AZ80 magnesium alloy during partial remelting was investigated. Furthermore, the tensile mechanical properties for AZ80 magnesium alloy thixoextruded from the starting materials treated by MAF were determined. For comparison, as-cast AZ80 magnesium alloy was also thixoextruded. The results show that the SIMA route produced ideal, fine semi-solid microstructure, in which almost completely spheroidal primary solid grains had a little amount of entrapped liquid. The microstructure of the as-cast alloy in the semi-solid state is less spheroidized compared with the MAF alloy under the similar isothermal holding conditions. With prolonged holding time, the size of the solid grain increases and the degree of spheroidization is improved in the MAF formed alloys. However, the solid grain size of the as-cast alloys decreases initially, and then increases with further increasing temperature. The tensile mechanical properties for AZ80 magnesium alloy thixoextruded from the starting material produced by MAF are better than those of AZ80 magnesium alloy thixoextruded from the starting material produced by casting. The ultimate tensile strength, yield strength and elongation of the alloy thixoextruded from the starting material produced by MAF are 314 MPa, 238 MPa and 14%, respectively.

Effect of combined RE–Ba–Sb addition on microstructure and mechanical properties of 4004 aluminum alloy

Abstract As a brazing foil, 4004 Al alloy has good welding performance. However, the high Si content decreases the plasticity of the alloy. In order to improve the plasticity of 4004 Al alloy and subsequently improve the productivity of 4004 Al foil, 4004 Al alloy was modified by RE–Ba–Sb. As a comparison, the 4004 Al alloy was also modified by RE with different addition. The tensile properties of the alloy reach the best when the addition of RE was 0.2%, in which the tensile strength and elongation were 194 MPa and 5%, respectively. For RE–Ba–Sb modification, the addition of three elements was optimized by orthogonal analysis. The results showed that the greatest impact parameter of RE–Ba–Sb modification was RE addition, followed by addition of Ba and Sb. The optimum addition amounts of RE, Ba and Sb obtained by orthogonal analyses were 0.01%, 0.3%, and 0.05%, respectively. The tensile strength and the elongation of 4004 Al alloy modified by the optimal modification process were 224 MPa and 6%, respectively. The amount of RE addition in RE–Ba–Sb modification is lower than that in RE modification.

Numerical simulation of macrosegregation with grain motion during solidification of Mg-4wt.%Y alloy

A two-phase solidification model was used that incorporates the descriptions of natural convection, heat transfer, solute transport and solid movement at macroscopic scale with microscopic relations for grain nucleation and growth. The implementation of the two-phase model was validated by comparisons with a consensus of previous numerical simulation for Sn-5wt.%Pb alloy and with experiment for Mg-4wt.%Y alloy cast in one-side-chilled resin sand mould. With free movement of globular grains in the bulk liquid, effects of melt superheat and nucleation density on fluid flow behavior and macrosegregation during solidification of Mg-4wt.%Y alloy were numerically investigated. It was found that a lower melt superheat and a higher nucleation density decrease the severity of macrosegregation by weakening the flotation of grains.

Influences of Rod Diameter and Sand-Mould Strength on Hot Tearing in Mg WE43A Constrained Rod Castings

Under conditions of changing sand-mould strength and rod diameter, hot tearing susceptibility of Mg WE43A alloys was studied using constrained rod casting solidified in a sand mould. Variations of temperature and shrinkage force with time during solidification of Mg WE43A alloy were recorded by means of a thermocouple and a force sensor. Susceptibility to hot tearing at hot section was decreased with increasing rod diameter from 10xa0mm to 20xa0mm. The rod with 10 mm diameter fractured, and the rod with 15 mm diameter presented hot tearing. No hot tearing was noted for the rod with 20 mm diameter. For the resin content of 1%, 1.5%, 2%, 2.5% and 3%, the tensile strength of sand mould was measured as 0.12, 0.18, 0.28, 0.17 and 0.15xa0MPa, respectively. The casting fractured at hot spot position for the sand mould with strength of 0.12xa0MPa. Hot tearing occurred at hot spot for the sand mould with strength of 0.15xa0MPa. No hot tearing was found at hot spot for the sand mould with strength of 0.28xa0MPa. The present research confirms that increasing the sand-mould strength and avoiding the entrapment of sand particles and the formation of gas pores during casting increase the resistance to hot tearing.

Effect of Hydrothermal Reaction Conditions on the Sizes and Morphologies of ZnO Nanorods

The influence factors of hydrothermal treatment on the formation process of ZnO nanorods are investigated involving with hydrothermal temperature, time and precursor concentration. The as-obtained products were characterized by Scanning Electron microscope (SEM) and X-ray diffraction (XRD), respectively. XRD result indicates that the obtained ZnO nanorods are high-quality single crystals. SEM results indicate that both the diameter and the length of ZnO nanorods increase with increasing the hydrothermal time and temperature. The precursor concentration prominently determines the morphologies of ZnO nanostructure from initial particle morphology to rod-like, and to final slice-like morphology.

Preparation of NiO coated aluminum borate whiskers by a solgel process and an ultrasonic dispersion technique

NiO coated aluminum borate whiskers were prepared by a sol-gel process and an ultrasonic dispersion technique. The preparation process and characterizations of NiO coated aluminum borate whiskers were investigated. The results show that during the heating process of the xerogel coated aluminum borate whiskers, one endothermic peak appears at 100 °C and three exothermic peaks appear in the range of 150-350 °C according to the differential thermal analysis. And no weight loss occurs after 350 °C according to the thermogravimetry analysis. After the xerogel coated aluminum borate whiskers are calcined at 500 °C, the surface of each whisker is uniformly coated by a layer of NiO film and the NiO coated whiskers can be easily dispersed in water through an ultrasonic apparatus. Moreover, No phase transformation of NiO and interfacial reaction between NiO and aluminum borate whiskers occur when the xerogel coated aluminum borate whiskers are calcined in the range of 500 and 900 °C.

Abrasion Behavior of WC Reinforced Cast Iron Surface Composite Fabricated by Cast-Infiltration Method

In this paper, WC particles and NH4HCO3 powders were mixed evenly, and then pressed under 150MPa. The WC porous preforms were obtained after the compacts being heat treated to eliminate NH4HCO3. The volume ratios of WC in the preforms were 30%, 40% and 50% respectively. WC/Fe composites were fabricated by infiltrating liquid cast iron into the WC porous preforms. Optic microscope and scanning electron microscope were employed to observe the microstructure of the matrix alloy and the composites. The results showed that matrix alloy without WC addition had pores in the surface. The microstructure of the composites with WC volume fractions of 30%, and 40% were denser than that of 50%. Hardness and wet sliding wear behaviors of the composites were investigated at room temperature. The addition of WC particles could effectively improve the hardness and the wear resistance of the composites. The influence of volume fractions on hardness of the composites was similar to that on wear resistance. The hardness and the wear resistance of the 40vol.%WC/Fe composite was better than those of the 30vol.%WC/Fe composite. And the properties of the 50vol.%WC/Fe composite were the worst.

Physical Simulation on Chill of Thick Walled Ductile Iron Casting for Spent-Nuclear-Fuel Container

Forced cooling measures need to be adopted in order to ensure the thick walled ductile iron casting solidification within the stipulated time. In this paper, the thick walled ductile iron casting for spent-nuclear-fuel container is used as the research object. The technology of outside mold has been identified in the actual production process. Through physical simulation experiment, the thickness of the outside the chills can be determined, and the cooling effect of chills is verified. The results show that cooling conditions have a decisive effect on the eutectic solidification, the residence time of eutectic platform and the time of casting solidification.