Porosity Control in Aluminium Foams Using Different Additives

Abstract

Abstract Ultra-light aluminium foams are often used as structural materials in aerospace and automobile sectors as they can provide good structural strength along with light weight. Melt based metal foams can be obtained by creating gas bubbles inside a liquid or semi-liquid metallic melt which has been pre-treated in a suitable way. Foaming techniques as direct or indirect foaming are practiced for production of these foams. Blowing of gas is used to create gas bubbles in direct foaming while blowing agents as metallic hydrides, which create hydrogen bubbles are used in indirect foaming. The properties of these metal foams are directly affected by nature of porosity and its distribution. Therefore theoretical studies needs to be developed to control the cellular structure and hence its properties. In present work, we have studied the effect of gas bubble rise velocity and melt viscosity, on pore size and its distribution in aluminium foam. A 142 PPI aluminium foam, prepared using indirect foaming technique having porosity ∼86 % is used. The bubbles generated by the blowing agent must be entrapped in the melt which finally result in formation of pores in metal foam on solidification. Our calculations suggested that bubble rise velocity and melt viscosity are responsible for vertical displacement of bubble in the melt. Melt viscosity opposes the bubbles rising and help them to stay in the melt, resulting in the porous structure. Based on our calculations, we have later measured how additives as Ca, Al2O3, SiC, TiB2, SiO2, BN influence the porosity inside aluminium foams.