Investigation of the influence of stabilisation additions upon the structure and properties of foam produced by semi-solid processing

Using expandometry, X-ray computer-tomography in combination with a newly-developed software for pore-size evaluation and compression tests, the influence of adding elements and particles upon foaming behaviour, structure and mechanical properties of AlSi6Cu4 foams based on thixocast precursor materials was investigated. Especially for In and for 3micrometer-Al2O3-particles, significant improvements of the foaming behaviour as expressed by the maximum expansion levels obtainable could be observed. In contrast, no major variation of compression strength was substantiated by the experimental data, the exception to the rule being Sn additions, which led to a deterioration of strength as consequence of unfavourable microstructural characteristics. Pore sizes, however, have invariably been found to decrease irrespective of nature and concentration of additions. Thus the study suggests that the use of additives of the kind evaluated here should be motivated by requirements regarding expansion performance rather than maximum strength. However, given the limited number of samples available, the influence of the observed structural changes on the scatter of mechanical properties could not be judged. Therefore, a continuation of the present study to verify the influence of mesostructural features on property variation at given densities may be considered worthwhile.