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The defense date of the thesis is 2010-08-27
The current date is 2019-04-24
URN etd-0827110-014731 Statistics This thesis had been viewed 2364 times. Download 0 times. Author Chi-Liang Gong Author's Email Address email@example.com Department Materials Engineering Year 2009 Semester 2 Degree Master Type of Document Master's Thesis Language zh-TW.Big5 Chinese Page Count 182 Title Refinement of Primary Silicon in an A390 Al alloy Keyword AlP Refinement Primary Silicon Hypereutectic Al-Si alloy Hypereutectic Al-Si alloy Primary Silicon Refinement AlP Abstract In this study, the effect of refinement on primary silicon in an A390 alloy by P-bearing chemical modifiers including Cu3P compound, Al-Cu-P and Al-Si-Cu-P master alloys was examined. Key variables governing the modification of primary silicon in A390 alloy, such as the amount of P added and the holding temperature and time of the alloy melt were analyzed. The results show that among three chemical modifiers the Al-Si-Cu-P master alloy produces the most satisfactory modification results, which were obtained under conditions of applying 0.016%~0.032% P and melt treating at 720℃~800℃ for a time span no
more than 210 minutes. Most of the primary silicon modification behavior can be explained fairly well by the heterogeneous nucleation of primary silicon at AlP particles, with the help of using an Al-P phase diagram constructed in this
study. In the case of applying 0.020% P and under 765℃ melt holding condition, the average particle size of primary silicon, d, was found to be
time-dependent. In the first hour (t = 0~60 minutes) d decreases from 35
μm to a minimum value of 25 μm. In the next two and half hours (t = 60~210 minutes) d remain in a well modified value of about 27 μm. When holding over 240 minutes a modification fading phenomenon (coarsening of primary silicon) was observed in the A390 alloy castings, in which d increases gradually from 31 μm to 43 μm when the holding time extended from 240 min to 480 min. The P-modification effect can be refreshed by either refilling modifier or a casting and re-melting process of the A390 alloy. The results also showed that the percentage of primary silicon-free zone is linearly proportional to the particle size of primary silicon.
Advisor Committee Chih-Fu Yang - advisor
Jien-Wei Yeh - co-chair
Jiun-Mu Chen - co-chair
Sheng-Long Lee - co-chair
Files Date of Defense 2010-07-29 Date of Submission 2010-08-27