Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7972795 | Materials Science and Engineering: A | 2018 | 27 Pages |
Abstract
Solidification microstructure, precipitation microstructure, and mechanical properties of foundry Al-Si-Cu-Hf alloy were investigated to elucidate the role of Hf during the solidification and precipitation processes. In the as-casting condition, α-Al dendrites, eutectic Si phases, and intermetallic compounds (Al2Cu, the needle-like β-Fe and Chinese-script α-Fe) were observed in the base alloy. However, no β-Fe was detected in the modified alloy, strongly indicating that Hf addition promotes the formation of the α-Fe phase but suppress the formation of the β-Fe phase. Furthermore, Hf addition can result not only in the formation of Hf-containing intermetallic compounds with different morphologies, which were identified as Si2Hf, but also, more importantly, in a significant decrease in the size, number, density, and volume fraction of porosity. After treatment with solution at 520â¯Â°C for 20â¯h, the formation of thermally stable Si2Hf precipitate was observed. After aging treatment at 180â¯Â°C up to 72â¯h, a delayed aging hardening was observed, which may be because Hf addition suppressed the formation of θ' precipitate. Clearly, Hf addition in Al-Si-Cu alloy can modify the solidification microstructure and the precipitation microstructure, which is believed to be beneficial for mechanical properties. Indeed, a significant increase in elongation by 51.4% without a sacrifice of strength was obtained, compared with the unmodified Al-Si-Cu alloy. This investigation highlights the importance of a well-controlled solidification microstructure and precipitation microstructure for the improvement of mechanical properties, in particular to elongation.
Related Topics
Physical Sciences and Engineering
Materials Science
Materials Science (General)
Authors
Yuan Xing, Zhihong Jia, Jiehua Li, Lipeng Ding, Huilan Huang, Qing Liu,