Static and dynamic energy absorption of Al foams produced by the sintering and dissolution process

Abstract

This article investigates the effects of the processing conditions of the novel sintering and dissolution process (SDP), including sintering temperature, sintering time, Mg addition, and cell size, on the capacities of the as-processed Al foams for static and dynamic energy absorption. While higher temperatures generally promote better bonding between the Al particles during sintering and, therefore, improved energy-absorption capacities, there exist optimum sintering times and cell-size ranges for producing Al foams with the best energy-absorption characteristics. The optimum sintering time increases when the sintering temperature or the relative density is decreased. The addition of a small amount of Mg powder to the Al/NaCl compact can enhance the sintering markedly and increase the energy-absorbing capacity of the foam by up to 50 pct. For any Al foam, the energy absorbed in the static condition is much greater than that in the dynamic condition. The mechanisms of these effects are also discussed.

Optimisation of compaction and liquid-state sintering in sintering and dissolution process for manufacturing Al foams

“…Like the other P/M processes, one of the most pronounced advantages of SDP is its flexibility. The present results and previous work [4,10] have shown that the cell size and porosity of the Al foams made by SDP can be varied in relatively wide ranges, typically from decades to thousands of microns and from 60 to 85%, respectively, which is difficult to achieve by the preform infiltration or the other foam-manufacturing processes.…”

“…7a and b, a large quantity of micro pores and interstices exist in the matrix of the pure Al foams. There is very little change in the matrix microstructure for the foam after 0.5 wt.% Mg addition, relative to the Al powder, as shown by comparing [10], the addition of elemental Mg powder did not seem to introduce a large difference in the liquid-state sintering of Al powder under the present conditions. When both Sn and Mg were added, both at 0.5 wt%, however, the foam exhibited a densified matrix as shown in Fig.…”

“…It is well documented that effective solid-state sintering of Al powder can only be achieved after a considerable amount of the oxide film at the surface of the Al particles is disrupted either by mechanical deformation during compaction or Mg reduction during sintering [5][6][7][8][9][10]. To achieve strong metallurgical bonding during liquid-state sintering of Al powder, the oxide film at the surface of the Al particles must also be first disrupted, otherwise, the oxide film of each particle will serve as a hard shell preventing the Al inside, even in the liquid form, from establishing direct contact with fresh Al in the adjacent particles.…”

“…The contacts between the Al particles, at which the oxide films have been ruptured during compaction would remain intact during sintering without further oxidation. Mg can also reduce the oxide films at the surface of the Al particles [9,10]. In liquid-state sintering, however, the particles in direct metal contact are largely fused together instantly when the metal is melted.…”

“…Mg acts as a solid reducing agent in the system because the free energies of formation of the resultant Mg oxides, MgAl 2 O 4 and MgO, are lower than that of Al 2 O 3 . Al foams have successfully been made by SDP via solid-state sintering by combining high compaction pressure and Mg addition [10]. However, solid-state sintering of Al/NaCl compact is a very time-consuming process and may not be practical for large-scale commercial applications.…”