Xinggang Li

High cycle fatigue properties of die-cast magnesium alloy AZ91D-1%MM

The high cycle fatigue properties of the die-cast magnesium alloy AZ91D containing 1% mischmetal (mass fraction) at a fatigue ratio of 0.1 were investigated. The difference in the microstructure between the skin and core region of the die-cast magnesium alloy was analyzed by optical microscopy. The mechanical property tests indicate that the values of the tensile strength, elongation and hardness are 185 MPa, 1.5% and HBS 70 +/- 3 at room temperature, respectively. The p-S-N curve (p=50%) of the die-cast magnesium alloy AZ91D-1%MM is determined and the mean fatigue strength corresponding to 3.8 X 10(5) cycles is 70 MPa. A linear relation between S and N(p) in log scale between 10(3) and 10(6) cycles is written with a equation. The mechanical properties are influenced by the casting defects. The fatigue life of the samples with minor defects is near to the upper limit of the fatigue life data. The fatigue fracture surface of the samples with minor defects possesses the mixed characteristics of quasi-cleavage, lacerated ridge and dimple and it is brittle fracture mode as a whole.

Effects of speed parameters on cold rolling process of double groove ball-section ring

Abstract Double groove ball-section ring is an important part of complex profiled-section rings and has been widely used in energy industries, and cold double groove ball-section ring rolling is a new plastic forming technology that can directly fracture seamless double groove ball-section rings with high-precision and high-performance. Because the speed parameters (including the rotational speed of driving roll and the feed rate of mandrel) affect the feed amount per revolution and play important roles in the stability of cold double groove ball-section ring rolling process and the quality of deformed double groove ball-section ring production, the effects of speed parameters on the variation of ring configuration and the variation of strain in cold double groove ball-section ring rolling process are investigated. The obtained results provide valuable guidelines for the selection of speed parameters in the practical cold double groove ball-section ring rolling process.

High flux PEO doped chitosan ultrafiltration composite membrane based on PAN nanofibrous substrate

Abstract A new method for fabrication of thin film nanofibrous composite (TFNC) ultrafiltration membrane with high flux containing a hydrophilic poly(ethylene oxide) (PEO) doped chitosan (CS) barrier layer and polyacrylonitrile (PAN) nanofibrous substrate was proposed in this study. First, PEO doped CS barrier layer was electrosprayed onto electrospun PAN substrate layer. Then, the deposited PEO doped CS layer was swollen to imperceptibly merge into an integrated barrier layer by acetic acid vapour treatment and chemically cross-linking in glutaraldehyde acetone/water solution to form a thin barrier film on the PAN substrate. The depositing time of electrospray and vapour treatment conditions were optimised to control the thickness of PEO doped CS layer. Oil/water emulsions system was used to evaluate the filtration performance of the as prepared composite membrane. It was shown that the TFNC membrane can perform well in the filtration of oil/water emulsions with permeate flux of 117·2 L m−2 h−1 and rejection rate of 99·0% at low pressure(0·2 MPa), and this membrane also exhibit good pressure resistance, for it showed higher flux (223·5 L m−2 h−1) with a high rejection rate (99·5%) at high operating pressure (0·6 MPa).

Hot deformation behavior of AZ40 magnesium alloy at elevated temperatures

Hot compression tests on AZ40 magnesium alloy were conducted on a Gleeble 1500d hot simulation testing machine in a deformation temperature range of 330 °C-420 °C and a strain rate range of 0.002-2 s-1. Hot deformation behaviors were investigated on the basis of the analysis of the flow stressstrain curves, constitutive equation, and processing map. The stress exponent and apparent activation energy were calculated to be 5.821 and 173.96 kJ/mol, respectively. Deformation twins and cracks located in grain boundaries were generated at 330 °C and 0.02 s-1, which are associated with a high strain rate and a limited number of available slip systems. With increasing temperature and decreasing strain rate, the twins disappeared and the degree of dynamic recrystallization increased. The alloy was completely dynamically recrystallized at 420 °C and 0.002 s-1, with a homogenous grain size of approximately 13.7 μm. The instability domains of the deformation behavior can be recognized by processing maps. By considering the processing maps and characterizing the microstructure, the optimum hot deformation parameters in this experiment were determined to be 420 °C and 0.002 s-1.