Papers by Author: Rui Zhao

Abstract: The compressive behaviors of AZ31-Zr foams using Ca particles as thickening agent and CaCO3 powder as foaming agent were investigated in this study. The porosity was about 48.7%~72.9%, pore size was between 0.43~0.97 mm, and homogenous pore structures were obtained. Mechanical properties of AZ31 Mg alloy foams were investigated by means of UTM. The cellular AZ31 Mg foams possess superior comprehensive mechanical properties. The energy absorption characteristics and the effects of compression behavior on the energy absorption properties for the cellular AZ31 Mg foams have been investigated and discussed. The results show that with the addition of Zr, the Mg alloy foam has the highest energy absorption value of 16.26 MJ/m3 and the hardness value of 81.8 HV, which is much higher than that of the foams fabricated without Zr.

Abstract: It is difficult to control the pore size and distribution of Mg alloy foam by melt foaming method using titanium hydride as blowing agent and extraordinary coarse pore structures is often found in the Mg alloy foams. Using CaCO3 instead of titanium hydride as blowing agent, AZ31 Mg alloy foams with small well structure, porosity 35.0~72.0 % and average pore size 0.04~0.16 cm could successfully be fabricated In this study; AZ31 Mg alloy foam with the holding time of 30s had the best energy absorption. The energy absorption value of AZ31Mg foam was 5.52MJ/m³. After that, AZ31 foams sample was polished and rusted. The thickness cells were analyzed by use of Metallurgical Microscope and software. Then SEM micrograph of AZ31 Mg alloy foam and EDS analysis of the cell wall.

Abstract: 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.

Abstract: Mg72.5Zn26Y1.5 quasicrystal alloys were investigated under different solidification conditions. The specimens of Mg-Zn-Y alloys with cooling rates from 13.2K/s to 69.8K/s were gathered by a designed multi-channel temperature acquiring system and then the microstructures and phase evolution of the alloys were analyzed. The results show that the precipitation temperature of icosahedral quasicrystal phase (I-phase) increased with cooling rate increased from 13.2 K/s to 69.8K/s. The microstructure was mainly made up of α-Mg, I-phase and Mg7Zn3 phase. Meanwhile, the quasi-crystalline morphology was significantly different in the experiments. It changed from five (six) petals to the big pentagon with the decreased cooling rate.

Abstract: Mg72.5Zn26Y1.5 (at.%) quasicrystal alloys were investigated under different solidification conditions. The cooling curves were gathered by the multi-channel temperature acquiring system and the corresponding microstructures were analyzed. The morphology, microhardness and volume fraction of quasicrystals were detailedly studied. The effects of cooling rate on the above three aspects were also studied and the relation schema among them were exhibited. The results show that the quasicrystal size tend to smaller, its microhardness and volume fraction gradually increased, and the quasicrystal morphology changed from bulk polygon to petal-like and finally changed to plat X-shape with the elevated cooling rate from 2.3K/s to 181.2K/s. However, the quasicrystal nucleation will be restrained and amorphous matter will be created if the cooling rate exceed the critical point which make against the formation of quasicrystals with high performance.

Abstract: 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.