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摘要
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, alpha-Al dendrites, eutectic Si phases, and intermetallic compounds (Al2Cu, the needle-like beta-Fe and Chinese-script alpha-Fe) were observed in the base alloy. However, no beta-Fe was detected in the modified alloy, strongly indicating that Hf addition promotes the formation of the alpha-Fe phase but suppress the formation of the beta-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 520 degrees C for 20 h, the formation of thermally stable Si2Hf precipitate was observed. After aging treatment at 180 degrees C up to 72 h, a delayed aging hardening was observed, which may be because Hf addition suppressed the formation of theta' 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.
- 出版日期2018-4-11
- 单位重庆大学
