Han Fu-Sheng

Effects of process parameters and alloy compositions on the pore structure of foamed aluminum

Abstract A study was carried out to understand the dependence of the structures of foamed aluminum (FA) on the process variables and to seek an effective measure to overcome the difficulties in preparation of FA by melt foaming process. The following variables were examined: thickening-stirring time, addition of thickening agent, foaming temperature, addition of foaming agent, and the solidification behavior of the alloy. It was found that the slurry viscosity and foaming temperature have very strong effects on the density of FA. Selecting a suitable thickening agent for a required density is very important. Excessive high foaming temperature would result in unnecessarily large pores and non-uniform distribution. It may become easier to obtain a uniform pore distribution if selecting an alloy that has a wider solidification range.

Grain Boundary Peak in a Foamed Zn-Al Eutectoid Alloy

We study experimentally the temperature spectra of internal friction (IF) and relative dynamic modulus (RDM) in a foamed Zn-Al eutectoid alloy. The specimens with macroscopic pores (0.5-1.0 mm) were prepared in an air pressure infiltration process. The damping behaviour of the foamed Zn-Al eutectoid alloy is characterized by IF. The IF and RDM measurements at a maximum surface shear strain of 20×10-6 have been made by using a multi-function internal friction apparatus at frequencies of 0.5, 1.0 and 3.0 Hz from room temperature to the equilibrium eutectoid isotherm of 277 °C, while continuously changing the temperature cycle. At low frequency, an IF peak is observed in the IF temperature curve. The IF peak is of a grain boundary, which is associated with the diffusive flux on a crystalline boundary between the like-phases of Al/Al. Its activation energy has been calculated to be 1.10±0.06 eV and the pre-exponential factor τ0 is 10-14 s in the IF measurements.

Zener Relaxation Peak in an Fe-Cr-Al Alloy

We have studied the temperature spectra of internal friction and relative dynamic modulus of the Fe-(25 wt%)Cr-(5 wt%)Al alloy with different grain sizes. It is found that a peak appears in the internal friction versus temperature plot at about 550°C. The peak is of a stable relaxation and is reversible, which occurs not only during heating but also during cooling. Its activation energy is 2.5 (± 0.15) eV in terms of the Arrhenius relation. In addition, the peak is not obvious in specimens with a smaller grain size. It is suggested that the peak originates from Zener relaxation.

Preparation of Mg55Ni35Si10 Amorphous Powders by Mechanical Alloying and Consolidation by Vacuum Hot Pressing

Amorphous Mg55Ni35Si10 powders are fabricated by using a mechanical alloying technique. The amorphous powders are found to exhibit a relatively high crystallization temperature of 380?C. The as-milled amorphous Mg55Ni35Si10 powders are consolidated successfully into bulk body by vacuum hot pressing technique. Limited nanocrystallization is noticed. The Vickers microhardness range of the Mg55Ni35Si10 bulk sample is 7834 to 8048?MPa. Its bending strength and compressive strength are 529?MPa and 1466?MPa, respectively.

Effect of Quenching on the Grain Boundary Relaxation in PM2000 ODS Alloy

Grain boundary relaxation in a Fe-based ODS alloy is studied by internal friction measurements. It is found that a grain-boundary peak appears at a lower temperature in the quenched specimens than that in the annealed specimens. The activation energy of the peak is H = 2.82±0.11 eV for the former while H = 2.53±0.08 eV for the latter. In addition, a new relaxation peak is observed at the high temperature side of the grain boundary peak in the quenched specimens with an activation energy of 4.41±0.25 eV. The height of the peak increases with increasing quenching temperature. The results suggest that both the shift of the grain-boundary peak and the appearance of the new peak are due to increasing vacancies by quenching that are favourable for the motion of the grain boundaries.