Enhanced ductility in Al-Si-Cu-Mg foundry alloys with high Si content
- PDF / 417,633 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 86 Downloads / 198 Views
NTRODUCTION
IN a recent publication, it has been shown that high levels of Si increase the ductility of Al-Si-Cu-Mg foundry alloys (in particular, alloy family 319) that contain high levels of Fe. The flow curves shown in Figure 1, and the quality index chart shown in Figure 2 (replotted from Reference 1) illustrate the reported effect. The compositions of the alloys represented in Figures 1 and 2 are listed in Table I, together with the main intermetallic phases present in their microstructures. Alloy 1, with low Si and Fe content, is quite ductile, while alloy 2, with its increased Fe content, exhibits very limited ductility. Alloy 14, on the other hand, with an increased Si content, is almost as ductile as alloy 1, despite its high Fe level. A similarly striking effect is observed in the sequence of alloys 1 / 5 / 17, in which an increased level of Si (as in alloy 17) improves the ductility of the alloy with high Cu content (5). In the alloy sequence 1 / 6 / 18, an even more dramatic effect is seen in the presence of high levels of both Cu and Fe. Alloys with high Mg and Fe contents exhibit the same effect,[1] but for clarity and brevity, they have been omitted in this current article. It is known that the Si content may radically change the primary aluminium grain structure, from a globular morphology at Si contents below about 6 pct to an orthogonal dendritic structure at higher Si levels.[2] It has been suggested[1] that these Si-induced morphological changes in the solidification structure may cause a refining of the Fe-rich intermetallic phases and a general dispersion of [1]
´ CERES, Associate Professor, and J.A. TAYLOR, Senior C.H. CA Research Fellow, are with the Co-operative Research Centre for Cast Metals Manufacturing (CAST), School of Engineering, The University of Queensland, Brisbane, QLD 4072 Australia. Contact e-mail: c.caceres@ minmet.uq.edu.au This article is based on a presentation made in the John Campbell Symposium on Shape Casting, held during the TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA. METALLURGICAL AND MATERIALS TRANSACTIONS B
the inter-metallic phases that form during solidification, leading to the observed increase in tensile ductility. However, only a limited metallographic study supporting these claims has been presented to date.[3] The object of this article is twofold: (1) to present a more comprehensive metallographic study of the effect of Si content on the phases present in each alloy, including a brief discussion of the refining mechanism of intermetallic phases, and (2) to assess their participation in the fracture process. The comparisons made in the present study are meant to demonstrate the effect of changing the Si content from low to high (i.e., 4.5 to 9 pct) while leaving Cu, Mg, Fe, and Mn levels constant. II.
MATERIALS
The alloys of the present work are part of a larger set of experimental alloys, the microstructural and mechanical property details of which have already been published.[1,4,5] The casting procedure and heat-treatment schedule have b
Data Loading...
