Effect of thermal condition on blowing behavior and pore morphology of porous magnesium

Abstract

Porous magnesium was fabricated from a precursor made of AZ91 magnesium machined chips. The effect of thermal conditions (heating rate, heating temperature and cooling rate) of the precursor on foaming behavior and pore morphology was investigated. The precursor started to expand at around the solidus temperature of AZ91 magnesium alloy, and accelerated its expansion rate after the temperature exceeded the liquids line. The maximum expansion was sustained only for a few seconds, and the specimen shrunk rapidly by heating the specimen continuously. The degree of maximum expansion became higher and the pore size became smaller by increasing the heating rate from 1 K/s to 3 K/s. The porosity of porous magnesium increased by increasing the processing temperature up to 660°C, whereas the pore size became larger and inhomogeneous. The cooling rate also turned out to be an important factor to maintain high porosity. With the low cooling rate, pores tended to collapse and porosity became lower during the cooling period.