Preparation And Mechanical Properties Of Pure Aluminum Foam By Vacuum Foaming

Aluminum foam with low density, good shock absorption, sound absorption and other characteristics, is widely used in aerospace, machinery, construction and other areas.But the conventional foaming method prepared aluminum foam has high cost foaming agent, low product rate, imperfect net forming process and other defects. In order to solve above problems, this paper presents a new method for the preparation of pure aluminum foam using vacuum foaming technology:Adding in very small amounts of TiH2 to increase the melt viscosity, injected foaming mold and then filling foaming under the effect of vacuum, at last obtained the pure aluminum foam materials. The advantages of this approach are low cost, uniformly controllable porous structure, net forming and so on. Based on preparation of vacuum foaming aluminum foam technology, compression performance, mechanism of initial porosity and filling, we get the following conclusions:(1) Uniform dispersed initial porosity was obtained by adding a small amount of foaming agent (TiH2) introduced gas. In this process, we found optimized process parameters:2wt% SiC and 0.4wt% Mg were added into the melt, the stir rate was 2000r/min and the time was 15min; after that,0.3 wt% TiH2 was added into the melt and dispersed by stir of 2000r/min for 2min, than the initial porosity was obtained.(2) The initial porosity of melt foaming filling under vacuum. the optimized process parameters of vacuum foaming is:the mold was preheated at 670℃, the vacuum degree was 15Pa, and the time of filling foaming was 30s; then the foamed aluminum was obtained after cooling for 5 min under vacuum condition. The obtained of pure foamed aluminum has the 75-85% porosity rate and the 0.5-5mm average particle size.(3)Along with the increase of porosity (75% to 85%), densification strain increased from 53% to 60%, the energy absorption rate reduced from 10.37MJ/m3 to 3.05MJ/m3. Densification strain and porosity were positively related. Energy absorption properties and porosity were inversely related.(4) lwt%SiC viscosity prepared pure aluminum foam has good compression performance. Its energy absorption is up to 8.3MJ/m3. The micro factors influencing the compression performance include:coarse grains, uneven distribution adding particles.(5) During the filling process, because the Reynolds number Re=2700, melt in the transition state of fluid, so the adjacent pores merged.(6) According to the characteristics of the vacuum foaming method, air pressure inside a bubble matches satisfy formulaPbubble=P0+ρgh+2σ/R. The filling process is divided into:initial status and growth stage and filling stage.