Potential New Matrix Alloys for production of PM Aluminium Foams

Abstract

The powder compact melting technique for aluminium foam production as practised today accepts a certain mismatch between foaming agent decomposition and matrix alloy melting temperatures. This mismatch is believed to influence the pore structure in an unfavourable way. Adjustment of TiH2 decomposition as well as liquidus and solidus temperatures of matrix alloys can be used to counteract it. Effects of TiH2 thermal treatments are investigated using thermal analysis. TiH2 variants gained via annealing treatments were used to produce aluminium foam precursor materials. As matrix for these specimens, aluminium based alloys with low liquidus and solidus temperatures were selected. Alloy systems considered include established combinations of aluminium with Cu, Mg, Si and Zn as well as special quaternary mixtures of these elements. First examinations presented include thermal analysis of alloys as well as studies on expansion vs. time and temperature relationships of precursor material based on new alloys and foaming agent variants.

Metal Foams: Production and Stability

“…3). There are many parameters which have been varied in such foaming experiments: -composition of alloy, [41,42] -oxide content of precursor, [23,[43][44][45][46] -type and content of additional ceramic particles [13,47,48] -type, [49][50][51] pre-treatment [13,52] and content of blowing agent, -manufacturing parameters of precursor, [41] e.g. pressure, pressing temperature and time,…”

Al and Zn Foams Blown by an Intrinsic Gas Source

“…[10] The intrinsic hydrogen content of AlMg50 powder is sufficient to achieve a moderate expansion both in Al-and Zn-based alloys, see Figure 1. In powder compact method, volume expansions of 350-650% for Al and Al-based alloys [21][22][23][24][25][26][27] and 600-1000% for Zn and Zn-based alloys [21,26,28,29] have been reported in the literature.…”

“…It is generally believed that a favorable foaming condition is when most (preferable all) of the metallic part melts before gas generation from the blowing agent in the sample begins [5,25,30,31] provided that there are sufficient numbers of gas nuclei in the material. [9] Among the alloys used in the present study, the Zn-based alloys fulfill this requirement quite well: the near eutectic Zn alloy containing 3.3 wt% Mg melts at 340 8C (see Table 1) which is almost at the onset (330 8C) of gas generation from AlMg50 powder and well below the gas evolution peak.…”

Metal Foaming Studied In Situ by Energy Dispersive X‐Ray Diffraction of Synchrotron Radiation, X‐Ray Radioscopy, and Optical Expandometry

“…[2][3][4][5][6] Pressing powder mixtures under vacuum or reducing the melting temperature by alloying Al with Si, Cu, Mg, Zn, or combinations of these elements are also successful strategies for producing foams of improved pore structure and properties. [7][8][9][10][11][12][13][14] However, the more alloyed Al is, the more complex is to predict how the decomposition of TiH 2 will be inside expanding foams.The correlation between regimes of H 2 release and phase transformations of both as-received TiH 2 and pre-oxidized TiH 2Àx powders under flowing Ar were recently clarified, by using a combination of in situ diffraction methods, thermoanalysis and electron microscopy that helped to develop core shell models to describe the decomposition of the hydride in both conditions. [15] However, studies on H 2 desorption from foamable precursor material made for example by the powder metallurgical route, show different behavior than the one from loose powders, [16,4,9] which suggests that the phase transformations of TiH 2 during foaming of Al-based alloys might be different.…”