Suitability of various complex hydrides for foaming aluminum alloys
- PDF / 491,063 Bytes
- 8 Pages / 584.957 x 782.986 pts Page_size
- 87 Downloads / 195 Views
Francisco García-Moreno,a) Catalina Jiménez, and John Banhart Structure and Properties of Materials, Technical University Berlin, 10623 Berlin, Germany; and Institute of Applied Materials, Helmholtz Centre Berlin, 14109 Berlin, Germany (Received 8 February 2013; accepted 5 April 2013)
Some hydrides that could replace TiH2 as the hitherto most suitable blowing agent for foaming aluminum alloys were investigated. Hydrides taken from the group MBH4 (M 5 Li, Na, K) and LiAlH4 were selected since these have not been studied in the past although their decomposition characteristics appear to be suitable. Foamable precursors of alloy AlSi8Mg4 were manufactured by pressing blends of metal and blowing agent powders. Powders, precursors and precursor filings were studied by mass spectrometry to obtain the hydrogen desorption profile. Foaming experiments were conducted with simultaneous x-ray radiographic monitoring. Two Li-containing blowing agents were found to perform well and can be considered alternatives to TiH2.
I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2013.110
hydrides are considered hydrogen storage materials for a future hydrogen economy they are (or will be) inexpensive materials.15–21 A comparison of hydrogen concentration for several borohydrides, TiH2 and LiAlH4 is shown in Fig. 1. We may assess the effect of the different blowing agents on foam production by either (i) considering the variation of theoretical foam expansion produced by a fixed mass fraction of blowing agent, e.g., 0.5 wt% as typically used for TiH2, or (ii) by reducing the amount of the respective blowing agent so as to achieve the same foam expansion as for TiH2. Reducing the blowing agent content has the advantage that the powder blend might be easier to compact, which in turn could have a positive impact on foaming.22 Furthermore, it could reduce costs significantly. The real situation is more difficult than suggested by Fig. 1. Theoretical maximum foam expansions are not reached in practice due to only partial liberation of hydrogen from the blowing agent at a given foaming temperature and after a given time and hydrogen losses occurring during foaming.23–25 Calculating the content of each hydride that would provide an amount of gas equal to that liberated by the benchmark blowing agent TiH2 is not possible without knowing the details of gas generation. Therefore, we decided to leave the mass fraction of each of the new hydrides fixed to 0.5 wt% for this exploratory study. This implies that some of the new hydrides might not be added in optimal quantities. Once the desorption behavior of the hydrides under foaming conditions is known one will be able to compare the hydrides on the basis of equal amounts of released hydrogen gas.
2436
Ó Materials Research Society 2013
TiH2 is the blowing agent most frequently used to foam aluminum alloys. This applies to the various melt routes and to the powder-based manufac
Data Loading...
