Study of aluminum foam stability control and mechanism of melt

It has been found that aluminum foam with superior mechanical and physical properties possesses a good prospect of application. However, only if the effective continuous preparation of high-performance aluminum foam was achieved by breaking through the technical bottleneck of stability control of low-viscosity aluminum melt foam, could be the aluminum foam generalized and applicated. For this reason, aluminum foam was prepared by Two-Step Foaming process (TSF) under the condition of precursor without significantly viscosifying in this paper. The average size and distribution of titanium carbide (TiC) particles in foamable precursor were detected as well as analyzed. Moreover, the grain refining effect of Al-5Ti-0.25C master alloy on pure aluminum, i.e. matrix of aluminum foam, was analyzed. The investigation has been carried out at last to study the stabilization mechanism of low-viscosity aluminum melt foam.The main results are as follows:1. Aluminum foam was prepared under the condition of precursor without significantly viscosifying. Samples with3.6mm～4.2mm average cell diameter and70～80%porosity were obtained.10%mass fraction of Al-5Ti-0.25C addition,50ton force of precursor compacting and695℃temperature of secondary foaming were optimum process parameters in this experiment.2. Dispersive distribution of agglomerate of micron-scale TiC particles was found in aluminum melt after the adding of Al-5Ti-0.25C master alloy, TiC content was proportional to Al-5Ti-0.25C additions. The grain refining effect of Al-5Ti-0.25C master alloy on pure aluminum was obvious, the grain of pure aluminum was refined to163μm in average size when the melt temperature was700℃and the addition of Al-5Ti-0.25C was1wt.%. However, the grain would not be obviously refined with the increasing of Al-5Ti-0.25C additions. The expected mechanical properties of aluminum foam, such as yield strength and energy-absorption capacity would be greatly improved when the grain of matrix materials was refined.3. Mechanism of stability control of low-viscosity aluminum melt foam was partly due to micron-scale TiC particles that could not tackify the aluminum melt significantly, it could stabilize the liquid foam against drainage, and then TiC could form certain structures of particles to reduce the interfacial tension of liquid-gas, it could separate neighboring liquid-gas interfaces. And it was partly due to addition of magnesium that could reduce surface tension of aluminum melt.From the research on stability control of low-viscosity aluminum melt foam as well as its mechanism, we could achieve the following expected goals. Firstly, a little increase in viscosity of foamable precursor could guarantee good fluidity of aluminum melt, and the foamable precursor could be made through continuous casting. Secondly, the preparation of aluminum foam with fairly uniform macro-pore structure was realized from the premise that there was a little increase in viscosity of foamable precursor. Thirdly, aluminum foam with high strength, high toughness and excellent energy-absorption capacity could be prepared with Al-5Ti-0.25C which can refine the grain of matrix materials. Finally, the mechanism of stability control of low-viscosity aluminum melt foam was achieved, that conclusions lay the academic foundation for continuous preparation of aluminum foam.