摩擦搅拌点焊于高强度车用AZ80-F镁合金接合之研究.DOC

摩擦攪拌點銲於高強度車用AZ80-F鎂合金接合之研究 Study of Friction Stir Spot Welding of High Strength Automotive AZ80-F Magnesium alloy 研究生：林建宏 Lin, Chien-Hung 指導教授：陳永昌, 曾光宏 Chen, Young-Chang, Tseng, Kuang-Hung 【摘要】 輕量化為目前汽車工業發展之主要目標之一，因此鎂合金之應用逐年增加，另外，由於摩擦攪拌銲接具有高品質與固態銲接特性，因此亦備受矚目，本研究主要探討應用摩擦攪拌點銲於高強度車用AZ80-F鎂合金接合之研究，首先利用結構-熱耦合有限元素方法進行實驗參數之模擬分析，探討銲接參數對銲接溫度場之影響；然後使用摩擦攪拌銲接機台進行AZ80-F鎂合金點銲實驗，並利用拉剪與拉伸試驗及奈米壓痕試驗，探討不同銲接參數對於銲點接頭機械性質之影響，最後以金相實驗觀察銲接顯微組織之變化。研究結果顯示，AZ80-F鎂合金摩擦攪拌點銲之銲接溫度場變化對轉速或壓力的敏感性遠超其它銲接參數，AZ80-F鎂合金接觸面之溫度皆呈均勻分佈情況，且可由溫度分佈之曲線分析判斷銲接是否成功。經由金相組織觀察得知，攪拌頭幾何形狀明顯影響銲接區各部位塑性流擾動與晶粒細化程度；其中，雙錐形攪拌頭具有最佳之效果，最後藉由不同銲接參數之機械性質測試結果，發現銲點強度具有隨轉速與壓力增高而增加的趨勢，但可成功銲接之轉速具有一臨界值，若超過此臨界值時，將導致銲點接合不良。 關鍵字：摩擦攪拌點銲、鎂合金、攪拌頭、銲接參數、顯微組織 【Abstract】 Lightweighting has become a key issue in automotive industries recently. Magnesium alloy, consequently, has become one of the major materials for structures. In addition, the solid-state bonding and other excellent features of the friction stir spot welding (FSSW) makes it inherently attractive for body assembly and other similar applications. This study aims to investigate the welding characteristics of the AZ80-F magnesium alloy of FSSW. A 3D finite element coupling model is employed to investigate the effects of welding parameters on the thermal-mechanical behavior of the welds. Then, the experimental samples are made by using FSSW process and, the tensile-shear test, direct tensile test, nano-indentation test and metallographic test are performed to understand the corresponding characteristics of the spot welds. The results show that the welding parameters of tool rotation speed and pressure are more sensitive to the temperature distribution of the welds. In addition, the temperature distribution curve can be used to evaluate the properties of the welds. The results obtained from microstructure observation reveal that the geometry of the tool has a strong effect on the plastic flow and grain size in the welds during the welding process. The welds with the dual-conical