Effect of strain rate on compressive properties of novel Zn12Al based composite foams containing hybrid pores

Novel Zn12Al based composite foams containing hybrid pores were fabricated by stirring technique followed by direct foaming of the composite melt using CaCO3 as a blowing agent. The structures of the composite foams contained pores in two forms. The first one of pores had close cell structure and was entirely contained within the microballoons, which were added into the Zn12Al matrix alloy. The second form of pores was due to releasing of gas because of the decomposing of blowing agent under the influence of heat. The microstructure of the composite foam showed that the interface between the microballoons and Zn12Al alloy matrix was sharp and free from micro porosities, indicating that a good interfacial bonding was developed between the microballoons and Zn12Al alloy. The compressive mechanical responses of Zn12Al and Zn12Al-microballoon foams were investigated at different strain rates (2 x 10(-3), 4 x 10(-3) and 6 x 10(-3) s(-1)). All the produced foams showed ductile compressive deformation at room temperature. The experimental results showed that the yield, plateau and plastic stress of composite foams were higher than those of Zn12Al foam. The yield, plateau and plastic stress of the composite foams significantly increased with increasing the strain rate. The strain rate sensitivity of the yield and flow stress was noted to be high. The composite foams exhibited higher strain hardening exponent than those of the Zn12Al foams at all strain rates studied in the present work. The energy absorbed during plastic deformation of all the foams significantly increased with increasing the strain rate. The energy absorbed of the Zn12-30 vol.% microballoons increased by about 90% with increasing strain rate from 2 x 10(-3) to 6 x 10(-3) s(-1). The strain rate sensitivity and absorbed energy of the composite foams were larger than those of the conventional foams, indicating that the foams produced in the present work are suitable candidates for applications wherein the metallic foams are used primarily for their energy absorption capabilities. (C) 2009 Elsevier B.V. All rights reserved.