A novel approach to produce Al-alloy foams

The stability of Al foams during processing is crucial to producing uniform Al foams. Once pores form during processing, no matter which conventional methods are used, the pores grow and/or merge into large ones, which could cause Al foams to ‘‘collapse’’. Therefore, it has attracted great attention of researchers to enhance the stability of Al foams during processing for improved quality of Al foams. A novel approach to produce Al-alloy foams, ‘‘Rheofoaming’’, is presented in this paper. A twinscrew rheomixer fitted with a gas inlet near the end cap is used in this work. The mechanism of this approach is firstly to increase the viscosity of semisolid slurry of Al alloy by adding sub-micron Al2O3 particles and then to mix N2 gas with the semisolid slurry using a twin-screw rheomixer, which can offer high shear rate and intensive turbulence. The gas pores in the semisolid slurry are stretched and broken into smaller ones in the rheomixer. Al foams are very stable during the processing due to small pore sizes and high viscosity of semisolid slurry. The microstructure of rheofoamed Al foams and the process of this new approach have been described in this paper