Study On Preparation And Property Of Foamed Aluminum And Simulation Of Bubble Behaviors In Melt Aluminum

In this paper,by means of melt foaming method,using oxidized TiH₂ as blowing agent,foamed aluminum with small pore size and uniform pore distribution can be fabricated by changing the tackifier?Ca?content,tackifying temperature,foaming agent content and foaming temperature.After oxide treatment at 400?,5 h+500?,1 h,oxide Ti₃O was formed on the surface of TiH₂ powder.Its start decomposition temperature increased by 80?and the maximum endothermic peak temperature increased by 60?,which is beneficial to better foaming effect at high temperature.With the increase of tackifier content,tackifying temperature,foaming agent content and foaming temperature,porosity shows a trend of increasing first and then decreasing but the average pore size shows the opposite trend.When the tackifier content,tackifying temperature,foaming agent content and foaming temperature are respectively2.5 wt.%,800?,1.5 wt.%and 615?,the best foaming effect can be obtained.The stress-strain curves of foamed aluminum can be divided into three stages:in elasticity stage,stress increases linearly with strain;in plastic stage,stress fluctuates slightly or is almost constant and obviously lags behinds strain,thus a wider yield plateau appearing;in densification stage,the stress increases rapidly with the increase of strain.Yield strength and plateau stress are gradually decreasing with the increase of porosity and average pore diameter.The unit volume energy absorption of foamed aluminum is closely related with porosity and average pore diameter and foamed aluminum with lower porosity and smaller pore diameter can absorb more energy.The floating characteristics of single bubble,two bubbles and bubble clusters in melt aluminum were simulated to get the influence of surface tension and melt viscosity on bubbles with Fluent Software.In the simulation,VOF technique was used to solve the free surface problem and source term was introduced to the volume fraction equation to consider the decomposition of foaming agent during the fabricating process of foam aluminum.The results show that two bubbles in a vertical line were prone to merge into single one during their floating process and thus cause violence disturbance of fluid which can aggravate the deformation and break of the bubbles.However,two bubbles in a horizontal line with a certain distance were apt to produce one pair or two pairs of vortexes which pushed the bubbles far from each other.Furthermore,with the increase of melt viscosity,the escape velocity of bubbles in the melt aluminum was reduced and bubbles had more time to merge and grow.With the increase of melt surface tension,the bubbles were more difficult to deform and thus more round pores can be obtained in fabricated foam aluminum.