Effect of metal powder size on the gas expansion behavior of 7075 Al alloy in a semisolid state

Gas expansion in a semisolid state at 903 K was quantitatively investigated from the viewpoint of the porosity, pore size and pore area for two kinds of 7075 Al alloy made of ∼25 and ∼355 μm powders. The pores were relatively uniformly formed and grown in a specimen made of the ∼25 μm powder. However, abnormally large pores of more than 500 μm in diameter were observed in the specimen made of the ∼355 μm powder, resulting from the nonuniform distribution of liquid phases. This points out the importance of a uniform distribution of liquid phases to reduce deviations in pore size.