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URN etd-0909114-194448 Statistics This thesis had been viewed 1276 times. Download 32 times. Author Chun-Chieh Peng Author's Email Address email@example.com Department Materials Engineering Year 2013 Semester 2 Degree Master Type of Document Master's Thesis Language zh-TW.Big5 Chinese Page Count 147 Title The Effects of Dispersoid-forming Elements on the Microstructures and Mechanical Properties of 7050 Al Alloys Keyword Al3Sc Al3Zr Al6Mn Dispersoid-forming Elements Recrystallization Recrystallization Dispersoid-forming Elements Al6Mn Al3Zr Al3Sc Abstract In this study transition metals of Mn, Zr and Sc were added into a 7050 Al alloy for the study of effects of Al-TM compound dispersoids on microstructure, recrystallization temperature and mechanical properties of 7050 Al alloy which has been subjected to under a couple of wrought alloy processing routes. In addition, the proper process conditions for various Al-TM dispersoids to exhibit their best functions on improving thermal stability and mechanical properties of the 7050 Al alloy were identified. The microstructure and the recrystallization temperatures of the heat-treated 7050 Al alloys containing various dispersoid-forming elements were examined by using OM and SEM. The effect dispersoid-forming elements and the precipitation reaction of Al-TM dispersoids on the mechanical properties of 7050 Al alloy were studied by using Rockwell hardness tester and tensile test.
The results showed that the precipitations of Al6Mn and Al3Zr dispersoids in 7050Mn (with addition of Mn) and the 7050Zr (with addition of Zr) alloys, through a special thermal (2-step dispersoid precipitation of 300°C/12h + 470°C/12h) and hot rolling processing route, exhibit proper results in terms of thermal stability ( inhibiting recrystallization), grain refinement and high tensile strength. Through the special 2-step dispersoid precipitation the 7050Mn and 7050Zr alloys exhibit excellent T6 tensile strengths of 583 and 585 MPa, respectively, which are 40 and 42 MPa in magnitude greater than that of 7050 Al alloy (543 MPa). On the other hand, the 7050Sc (with addition of Zr) would precipitate Al3Sc dispersoid properly through the other type of wrought alloy processing route, which is without the 2-step dispersoid precipitation. This type of processing rendered the 7050Sc alloy with proper thermal stability, grain refinement and high tensile strength up to 591 MPa. But if the 7050Sc alloy was processed with the 2-step dispersoid precipitation, its thermal stability (recrystallization temperature) and mechanical properties would drop significantly; the T6 tensile strength dropped to 573 MPa. As for the 7050X ( multi-addition of Mn, Zr and Sc) alloy, with composite Al-TM dispersoids the alloy exhibit the best thermal stability, grain refinement and tensile strength (up to 643 MPa in T6 condition) under a wrought alloy processing route without 2-step dispersoid precipitation.
Advisor Committee Chih-Fu Yang - advisor
Chum-Mu Chen - co-chair
Jien-Wei Yeh - co-chair
Sheng-Long Lee - co-chair
Files Date of Defense 2014-07-29 Date of Submission 2014-09-10