Al-Mg系5052鋁合金為一固溶強化材，具有強度佳、加工容易、耐蝕能力強等優點，常被應用汽車側構骨架之板材。在現今的汽車工業，應用在接合鋼件的電阻點銲，會由於鋁合金的電熱傳導率較高，使得電量的消耗較大，電極的壽命也跟著降低，因此電阻點銲並不適用於接合鋁合金。摩擦攪拌銲接(FSW)為一固態接合技術，由於過程中溫度未達熔點，故無氣孔、凝固裂紋等傳統熔融銲接產生之缺陷，所以特別適合鋁合金銲接之應用。摩擦攪拌點銲(FSSW)為摩擦攪拌銲接的衍生，而不同的攪拌頭(Probe)長度與點銲時間會影響其接合的破壞荷重，因此本研究改變攪拌頭的長度與點銲時間，探討不同攪拌頭的長度與點銲時間對其機械強度的影響，並對所得到的實驗數據利用韋伯分佈函數做可靠度分析。
實驗結果顯示，當攪拌頭長度相同時，特徵壽命隨著點銲時間增加而上升。在相同點銲時間，特徵壽命隨著攪拌頭長度減短而下降，藉由光學顯微鏡觀察不同攪拌頭長度點銲後之橫切面，發現攪拌頭長度愈長，深入試片的深度愈深，使得兩試片之間界面被塑性流往上帶的程度愈大，導致破壞荷重變大；而相同的攪拌頭長度，點銲時間愈長，試片之間接合程度增加，裂縫減少，破壞荷重變大，但彼此破壞荷重分佈範圍並不一致，
韋伯分析結果顯示，不同攪拌頭長度不同點銲時間之韋伯模數m值皆大於1，屬於磨耗破壞型。攪拌頭長度為2.5mm時，90s(秒)與105s(秒)之試片平均破壞荷重、最大破壞荷重與可靠度相近，再考慮成本因素，點銲時間90s為較佳條件；攪拌頭長度1.5mm時，120s之破壞荷重與可靠度皆較佳，為較佳條件；攪拌頭長度1.0mm時，135s之破壞荷重與可靠度較佳，為較佳條件。在相同點銲時間下，攪拌頭長度2.5mm明顯較1.5mm與1.0mm有較大的破壞荷重及較高的可靠度，為較佳條件。綜合上述結果，攪拌頭長度2.5mm點銲時間90s為最佳條件。

Al-Mg series aluminum alloy is a solid-solution strengthening material. Because of its good mechanical strength, easier manufacturing and good corrosion resistance, it has been used in inner panels of side carcass of the automobile body. Resistance spot welding is widely used in the automotive industry for steel joining. However, this process is not suitable for aluminum alloys because of the higher electrical and thermal conductivities. Then it will lead to higher energy consumption and reduce electrode life. Friction Stir welding (FSW) is a solid-state joining process. Because it will not reach the melting point of the alloys during the process, there is no porosity and shrinkage that usually accompany with fusion welds. So that it is especially suitable for welding aluminum alloys. Friction stir spot welding (FSSW) is a derivative process of the friction stir welding. The failure load of joints will be affected by using different probe length and welding time. In this study, by changing the probe length and welding time, we will discuss the effect in mechanical strength of the alloys and to analyze the reliability of the experimental data by using Weibull distribution function.
The result of tensile tests shows that the characteristic life increases with increasing welding time when using the same probe length. At the same welding time, the characteristic life decreases with decreasing probe length. The optical microscope is used to observe the cross sections of different probe length specimens. The longer probe length is applied, the deeper the penetration depth. Then it result in larger degree of the interface upward between two specimens because of plastic flow and larger failure load. With the same probe length, the nearly full metallurgical joint increases and cracks decrease as increasing welding time, thereby the larger failure load. But the distribution range of failure load is not the same with each other.
The results of Weibull analysis show that the Weibull moduli of all the experimental parameters are wear-out failure modes. In 2.5mm probe length, the average, maximum failure load and reliability of 90s(second) are similar to 105s(second). Then concern the cost factor, the 90s welding time is a better condition. In 1.5mm probe length, the 120s welding time is a better condition because of its higher failure load and reliability. In 1.0mm probe length, the welding time 135s is a better condition not only the higher failure load and reliability but its failure rate upwards in a smaller load range. At the same welding time of 105s, the failure load and reliability of 2.5mm probe length are obvious bigger than 1.5mm and 1.0mm, thus 2.5mm probe length is better. Concluding above all, 2.5mm probe length with 90s welding time is the best welding condition.

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