- 學位論文
AZ31B鎂合金與6061鋁合金摩擦攪拌焊接材料之六氟鋯酸化成處理
Hexafluorozirconate Conversion Coating on AZ31B and 6061 Friction Stir Welding
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摘要
本研究使用的材料為AZ31B鎂合金與6061-T6鋁合金進行摩擦攪拌異質焊接，第一部份的研究著重於利用SEM進行焊接後的微結構分析，並搭配XRD與EBSD進行焊道區的相鑑定。將拋光完後的試片分為焊道外鎂、鋁基材的表面形貌以及焊道區的表面形貌進行討論，其中焊道區內又分為四個部分，分別是二次相、介金屬相、焊道區的鎂、焊道區的鋁。焊道區的二次相含有來自6061鋁合金的鋁鐵矽相、鎂矽相以及來自AZ31鎂合金的鋁錳相，由SEM的結果顯示，在焊道區可以觀察到二次相大量聚集或是呈現帶狀分布的現象，而這些二次相的成分以鋁鐵矽相與鎂矽相為主，較少觀察到鋁錳相。介金屬相為Al3Mg2和Al12Mg17，由鋁鎂原子的交互擴散所形成，在焊道內可觀察到相的分布符合擴散理論，與鋁相連的介金屬相為Al3Mg2，與鎂相連的為Al12Mg17，而Al12Mg17 +Mg兩相共存區的出現則說明此摩擦攪拌焊接試片非典型的二元擴散偶。焊道區內的鋁和鎂則和焊道外的鋁和鎂表面形貌相同。 第二部分著重於六氟鋯酸化成後的微結構分析，並提出於焊道區內的成膜機制。在鋁鐵矽相以及鋁錳相等比基材鈍態的二次相上可以觀察到較厚的化成膜。在介金屬相的部份，Al12Mg17比起Al3Mg2表面有較多白色的鋯顆粒，Al12Mg17 +Mg兩相共存區表面也覆蓋白色的鋯顆粒，鎂的表面可觀察到棉絮狀的鋯顆粒，鋁的表面則相較於其他相較平整。經由TEM的分析顯示，化成膜為雙層結構，外層推測為ZrO2、內層則為金屬氧化物，其中Al12Mg17 和Mg的金屬氧化物內含有氟的成分。在膜層厚度的部份，ZrO2膜層厚度Al12Mg17 > Mg> Al3Mg2 ≅Al，氧化層厚度Mg > Al12Mg17> Al3Mg2 > Al。最後基於化成後表面微結構影像、TEM化成膜成分與厚度分析提出了成膜機制。
並列摘要
The material used in this study is AZ31B magnesium alloy and 6061-T6 aluminum alloy of friction stir welding. The first part of the study focuses on the microstructure analysis after welding, while XRD and EBSD are used for phase indentification in the stir zone. The discussion of surface morphology is divided into three sections: magnesium substrate, aluminum substrate and stir zone. Among which the stir zone area was further divided into four parts, namely secondary phase, intermetallic compounds, magnesium in stir zone, and aluminum in stir zone. The second phase in the stir zone contains Al-Fe-Si and Mg-Si phases from 6061 aluminum alloy, and Al-Mn phase from AZ31 magnesium alloy. The SEM results indicate that aggregation of second phases can be observed in the stir zone, which are mainly Al-Fe-Si and Mg-Si phases, whereas Al-Mn phase is rarely observed. The intermetallic compounds are Al3Mg2 and Al12Mg17, which are formed by diffusion of Al and Mg atoms. The distribution of the phases in the stir zone is in accordance with the diffusion theory, where the intermetallic compound adjacent to Al is Al3Mg2 and the intermetallic compound adjacent to Mg is Al12Mg17. The surface morphology of Al and Mg in the stir zone is similar as that of Al and Mg outside the stir zone. The second part of the study focuses on the microstructure analysis after conversion coating. Thicker films are observed on the Al-Fe-Si and Al-Mn second phases which are more noble compared to the base material. The surface of Al12Mg17 has more white Zr particles than that of Al3Mg2, and the two phase region of Al12Mg17 +Mg is also covered with Zr white particles. Cotton-like Zr particles can be observed on the surface of Mg, while the surface of Al is relatively smooth compared to others.The TEM analysis shows that the conversion coating film is a two-layer structure, the outer layer is speculated to be ZrO2 and the inner layer is metal oxide. It is observed that the metal oxide layers of Al12Mg17 and Mg contain fluorine. The thickness of ZrO2 layer is Al12Mg17 > Mg > Al3Mg2 ≅ Al, and the thickness of metal oxide layer is Mg > Al12Mg17 > Al3Mg2 > Al. Al last, a film formation mechanism was proposed based on the microstructure image and TEM analysis of the composition and thickness after conversion coating.
參考文獻
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