Foaming and Filling-in Behavior of Porous Aluminum in Hollow Components

Abstract

Porous aluminum (aluminum foam) was fabricated by a powder processing route. TiH₂ powder was blended with Al powder as a blowing agent. The blended powder was then consolidated to make a precursor. When the precursor was heated, the TiH₂ powder started to decompose and hydrogen gas expanded in molten aluminum. Physical properties of the porous aluminum strongly depend on both porosity and pore morphology. In this research, pore morphology was characterized by an image analyzing software. Manufacturing temperature and heating time affected the pore morphology significantly. The manufacturing temperature should be in an adequate range. When the manufacturing temperature was low, the precursor did not expand sufficiently. The life-time of the pores became shorter when the temperature was too high. Although the pores at the initial stage of the blowing process were small (<0.5 mm) and relatively spherical, the pores become larger and irregular as the heating time became longer. A molding technique of porous aluminum in hollow parts becomes indispensable when porous aluminum is applied to automobile components The precursor was heated in a hollow pipe and the specimen was cut in both vertical and horizontal sections to investigate the filling-in behavior of the precursor. In the beginning of the expansion, the precursor expanded in a radial direction of the pipe. After the cross section of the pipe was filled, then the precursor expanded along the longitudinal axis. Heating profile was one of the most important factors which determines the possibility of filling-in behavior and the porosity of porous aluminum. Another important factor turned out to be an aspect ratio of the precursor.