Papers by Author: C.H. Chiang

Abstract: The extrusion forces of the spray-formed Al-25wt%Si alloy at various strain rates and temperatures were calculated with the flow stresses obtained from high temperature compressive tests. The compressive stress-strain curves of the spray-formed Al-25wt%Si at various temperatures and strain rates were determined and discussed. The constitutive equation of strain rate as a function of stress and temperature described by, n Q RT A e ' / sinh( ) − ε& = ασ for the spray-formed Al-25wt%Si alloy, was established. The activation energy and constants in the constitutive equation were discussed and compared to other Al alloys. A direct extrusion experiment was employed to evaluate the extrusion loads vs. ram displacement at various temperatures and strain rates. By applying the constitutive equation, the extrusion loads were calculated and compared to the experimental ones for various temperatures and strain rates. The accuracy of the calculated results compared to the experimental results was discussed.

Abstract: The coarsening behavior of spray-formed A-35wt%Si and A-45wt%Si alloys in the semisolid state were studied. The coarsening kinetic and Si size distributions after coarsening at various temperatures and times in the semi-solid state were investigated. The coarsening exponents, n, the rate constants, K, in the LSW theory, and the modified rate constants were determined from previous works. The coarsening activation energies of the two spray-formed alloys were calculated from the slopes of ln(KT) vs. 1/T plots. The Si size distribution functions after holding at various temperatures and times in the semisolid state were determined for the two spray-formed alloys. The effects of the stokes-motion in addition to pure diffusion mechanism on the variations of coarsened Si size distribution were also investigated.