Zhi Feng Wang

Study on Defects of A356 Aluminum Alloy Wheel

This paper studied the effects of inclusion and slag on properties of a die cast A356 alloy wheel. The result showed that the rate of defect is important for the mechanical properties. The tensile strength and extension was not dropped but the rate of defect is increased about 2%. The variation trend of tensile strength and extension is linear, while the area of porosity on tensile fracture is between 2% and 6%. However, the tensile strength and extension was dropped with the increasing rate of defect. The variation trend of mechanical properties of the sample with inclusion is stable, but the sample with slag is not stable. The mechanical properties of samples with inclusion are drastically changed, while the rate of defect is increased. The mechanical properties of samples with slag are smoothly. The EDS analysis indicated that the defects consist of Al-Ti-B compound, α-phase (Al12FeSi), β-phase (Al9Fe2Si2) and Al2O3. These oxides form the compact composite oxide film expand into first cracks. The fracture mode of sample with defects is brittle fracture. The values of the Secondary dendrite arm spacing (DAS) in the inclusion and the matrix are the same, while the values of DAS in the slag and the matrix are different.

Effect of Rare-Earth Elements on the Ignition-Proof Behavior of Industrial Pure Magnesium

The purpose of this research is to investigate effect of rare-earth elements (Y and Dy) on industrial pure Mg through the ignition point test and oxide film analysis. The results show that the 0.5%Y can make the ignition point of pure magnesium about 30°C higher. However, the ignition point of pure magnesium can be multiplied about 50°C by the mixed additions of 0.5wt%Y and 5wt%Dy. The SEM analysis indicates the oxide film of Mg-0.5Y-5Dy is more compact and tenacious than that of Mg-0.5Y. The XRD analysis indicates that the oxide film of Mg-0.5Y-5Dy consists of MgO, Y2O3 and Dy2O3. The most of all the three oxides are Dy2O3, which can prevent magnesium from further oxidizing.

Effect of Mg-Nd Master Alloys on Ignition-Proof Performance of AZ91D Magnesium Alloy

This paper studied the effect of Mg-Nd alloys on the ignition-proof performance of AZ91D magnesium alloy. The results showed that 0.5%Nd decreased the ignition point of alloy for about 20°C, but the ignition point could been multiplied with the adding of Nd element. When the content of Nd reached 5%, the ignition point increased about 40°C compared with AZ91D alloy. The ignition point reduced after the addition of 0.5%Nd can be attributed to the decrease of the solidus temperature and liquidus temperature. The further analysis indicated Nd and Al formed Al3Nd first, which consumed the content of Nd, so that the alloy didn’t have enough Nd to form Nd2O3 to protecting the alloy. The EDS analysis indicated when the addition of Nd reached 5%, competent Nd2O3 could be formed and compact oxide film which consisted of Nd2O3, MgO and Al2O3 was formed to prevent alloys from oxidation and combustion.

Monolithic Nanoporous Copper with Novel Electrochemical Properties Fabricated by Dealloying Cu-Zr(-Al) Metallic Glasses

Monolithic uniform nanoporous Cu (NPC) ribbons with a ligament/pore size of 10-25 nm are successfully synthesized by chemical dealloying the Cu50Zr50 and Cu50Zr45Al5 metallic glasses in 0.5 M HF for 7 min. It is found that the length scale of ligaments/channels can be tuned by simply alloying 5 at.% Al to the Cu-Zr binary glassy alloys. The current signal of the NPC-supported MnO2 composite electrode is remarkably enhanced as compared to that of pure MnO2 powders. These new findings greatly raise the hope for possible applications of NPC as a new type of electrode substrates or an advanced sensor in green and new energy technology.

Study on Fabrication, Defects and Compression Properties of Al Foams at Different Foaming Temperatures

Using Al powder as thickening agent and CaCO3 powder as foaming agent, Al foams with above 85% porosity, pore sizes between 1mm and 4mm and relatively uniform pore structure have been fabricated by melt foaming method at different foaming temperatures. Meanwhile, the paper researched the effect of foaming temperature on foaming effect and analyzed the defects in Al foams. At last, compression test were taken in order to investigate the mechanical properties of aluminum foams. The results showed that pore structure, pore distribution and compression properties of Al foams fabricated at 720°C were much better than that fabricated at lower temperature.

Effects of Spinning on Microstructure and Mechanical Properties of A356 Alloy

The tube-shaped parts of A356 alloy were deformed from 0% to 83% by spinning process. The microstructure and mechanical properties of A356 alloy were discussed. The results showed that as the wall thickness reduction increases, the dendrite cells of cast alloy are lengthened gradually and the average Secondary Dendrite Arm Spacing (SDAS) is reduced from 37.2μm to 23μm and eutectic silicon particles are distributed orderly along the spinning direction. The coarse acicular β-Al5FeSi is broken into many sections, and its length is reduced from 37.5μm to 12.5μm in the cross-section. The tensile strength and elongation exhibit a strong dependence upon the variation in wall thickness, with a parabolic relationship. The tensile fractured surface of parts with deformation ratio above 35% exhibits many equiaxial dimples, with intergranular ductile fracture mode.

Effect of Mn and Cu on Spheroidized Process of Mg-Zn-Y-Based Icosahedral Quasicrystal Phase

In-situ spherical icosahedral quasicrystal phase (I-phase) was fabricated in Mg-Zn-Y-based alloys by metal mold casting route. The effects of Mn and/or Cu on spheroidized process, morphology and microhardness of primary I-phase were studied in this paper. The results showed that the solidified morphology of I-phase depended on the stability of spherical I-phase during the subsequent growth and critical radius Rr of the spherical I-phase. Only when actual radius smaller than critical radius Rr can spherical IQC be formed. The effects of the fourth component and degree of undercooling on Rr were studied for the first time. Amazing spherical minisize IQC had been produced by improving cooling rate using a water-cooled copper mold. Multicomponent spherical IQC is hopeful of being strengthening phase to novel metal composites.

Morphologies of Quasicrystal Phase in Ternary Mg-Zn-Y Alloys

The paper studied various morphologies of the quasicrystal phase in Mg-Zn-Y alloys caused by different cooling rates. The cooling rates were reached through five kinds of cooling media. The cooling curves were monitored by multichannel data acquisition cards. A further heat treatment was made to study quasicrystal growth behavior. The results showed that, with the decrease of cooling rate, the quasicrystal morphology changed and its size became larger. Moreover, a planar quasicrystal morphology evolution schematic diagram during quasicrystal growth process was observed for the first time.

Thermodynamics and Dynamics Study on Solidification Process of Mg3Zn6Y Quasicrystals

Thermodynamics and dynamics of Mg3Zn6Y quasicrystals in solidification process were detailedly studied in this paper. The free energy, nucleation rate and nucleation energy were deduced and calculated. It shows that the driving force and nucleation rate gradually increase with the decreased temperature. The further studies show that the nucleation energy increase gradually with the decreased liquidus temperature. And it is apt to quasicrystal nucleation by increasing the cooling rate in a proper temperature range.

Heat Treatment and Morphology Study of Mg-Zn-Y Quasicrystal Alloys

Mg72.5Zn26Y1.5 quasicrystal alloys were treated under different heat treatment process. The microstructures of the alloys were investigated. The quasicrystal and eutectic morphologies and their transformation during heat treatment process were detailedly studied. The results showed that lamellar and dendritic eutectic phases throughout the matrix were evidently formed under heat treatment process 310°C×30min water quenched and 310°C×30min liquid nitrogen deep cooling, respectively. Furthermore, quasicrystals of dragonfly-like and bulk polygon morphology were formed under heat treatment process 575°C×15min water quenched and 700°C×2min cooled with furnace, respectively. Various morphologies’ transformation mechanism during heat treatment process were also studied.