Abstract
The microstructure of a high-pressure die-cast hypereutectic A390 alloy, including PSPs, pores, α-Al grains and Cu-rich phases, was characterized using synchrotron X-ray tomography, together with SEM, TEM and EBSD. The Cu-rich phases exhibited a net morphology and distributed at the boundaries of the α-Al grains, which in turn surrounded the PSPs. Statistical analysis of the reconstructed 1000 PSPs showed that both equivalent diameter and shape factor of the PSPs exhibited a unimodal distribution with peaks corresponding to 25 μm and 0.78, respectively.) PSPs morphology with multiple twinning were observed and morphological or growth transition of the PSPs from regular octahedral shape (with a shape factor of 0.85 was mainly caused by the constraint of the Cu-rich phases. In particular, the presence of the Cu-rich phases restricted the growth of the α-Al grains, inducing stress on the internal silicon particles, which caused multiple twinning occurrence with higher growth potential and consequently led to growth transitions of the PSPs.
Highlights
The wear property of the hypereutectic Al-Si alloys could be significantly improved by the primary silicon particles (PSPs)[1,2,3,4]
We employed synchrotron X-ray tomography to characterize the 3-D morphology of the PSPs in a hypereutectic A390 alloy processed using high pressure die casting (HPDC)
Further analysis via SEM, TEM and EBSD was performed on the solidification microstructure with particular attention focused on the interaction between PSPs, α-Al dendrites and Cu-rich phases to disclose the underlying mechanism that controls the morphological transition of the PSPs
Summary
The wear property of the hypereutectic Al-Si alloys could be significantly improved by the primary silicon particles (PSPs)[1,2,3,4]. Raghukiran et al.[24] found that the Al-Si-Sc alloy exhibited significantly high wear performance because both morphology and size of silicon particles were altered by adding Sc. to the best knowledge of authors, very limited work has been performed to investigate the Cu effect on the PSPs, e.g. in a A390 alloy which is extensively applied in aerospace and automotive industries. A TOYOBD–350V5 cold chamber die casting machine was applied to produce standard tensile testing bars (ø 6.4 mm) and Fig. 1 shows the sample configuration, together with the processing parameters[27,28]
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