1050-O純鋁電阻點銲之銲核形成及接合強度之可靠度分析

Abstract

由於鋁合金1050性質接近純鋁，質輕且散熱性良好，成形性佳，對於散熱要求日趨嚴格的3C產業，純鋁或鋁合金的使用將會愈來愈普遍，且其電阻點銲的接合技術也日益重要。但就現今的鋁合金電阻點銲而言，接合方式仍有待改善，且在直流式點銲機昂貴而市面上仍以單相交流點銲機為主的情況下，純鋁電阻點銲的應用勢必會受到限制。 本研究利用大型單相交流點銲機來進行鋁合金1050-O商用材點銲。在不同電阻點銲製程參數(熔接電流、通電時間及電極加壓力)下，針對不同厚度之鋁合金1050的銲核成長及拉剪強度作探討，且進一步尋求微硬度、銲核大小、拉剪強度與點銲製程三參數間的關係。最後取最佳製程參數範圍的拉剪強度值，利用韋伯分佈函數來探討鋁合金1050-O點銲後接合強度的可靠度。 由銲核微觀組織與微硬度試驗結果得知，銲核附近組織可區分為三個區域，分別為熔融區、熱影響區及母材。熔融區的微硬度值最高，母材微硬度值次之，熱影響區的微硬度值最低。且在適當的銲接條件下，銲核的微硬度會隨著通電時間和熔接電流的增加而下降，也會隨著電極加壓力的增加而增加。而銲核尺寸則會隨著熔接電流和通電時間增加而增加，隨著電極加壓的增加而下降。 由於實驗材料三種板厚的實驗結果具有相同的趨勢，本研究內容以1mm板厚試片的實驗結果為例，敘述製程參數與拉剪強度間韋伯解析之相關性。由二參數韋伯可靠度分析結果得知，在使用單相交流點銲機進行單點搭接之點銲時，銲後點銲件的接合強度之韋伯模數均大於1，屬於磨耗故障型。另外，在熔接電流固定且考慮最小壽命(t0)的情況下，通電時間10cycles和電極加壓力100kgf是本研究製程參數中最能預測極限拉剪強度值之銲接條件，同時也是二參數韋伯模數中，可靠度最佳的銲接條件。故本研究1mm相對最佳製程參數為熔接電流17.3kA，通電時間10cycles，電極加壓力100kgf。 且由相同的實驗方法得知，0.8mm的最佳製程參數為熔接電流17.3kA，通電時間10cycles，電極加壓力60kgf。而1.2mm試片的最佳製程參數為熔接電流17.3kA，通電時間13cycles，電極加壓力100kgf。

Because of the properties of 1050 aluminum alloy close to pure aluminum, it has good thermal conductivity and formability. For the 3C industries requiring for strict thermal conductivity, the use of pure aluminum or aluminum alloys will be more and more popular and so be the jointing technology of resistance spot welding. As far as the resistance spot welding of aluminum alloys, the method of joint still needs to be improved. Due to the expensive cost of the kinetic-energy machines, the single-phase welding machines are still the major in the market. Therefore, the application of resistance spot welding of pure aluminum must be limited. The purpose of this study is to use single-phase A.C. welding machine to connect 1050-O commercially pure aluminum. Under different welding parameters, aiming at the discussion of the nugget growth and tensile shear strength of different thickness of 1050 aluminum alloy, there is a further point which seeks a correlation between the microhardness, nugget size, tensile shear strength and welding parameters. Eventually, we take the value of tensile shear strength in the best range of welding parameters and then use the function of Weibull distribution to discuss the reliability of the jointing strength of spot welded 1050-O aluminum alloy. According to the experimental results of metallographic studies and microhardness test, the hardness in the fusion zone is highest, the base metal is second and the heat-affected zone is lowest. In proper welding conditions, when the holding time and welding current increase, the hardness in the nugget decreases. However, when the electrode force increases, the hardness increases. Furthermore, when the holding time and welding current increase, the nugget size increases. Unexpectedly, when the electrode force increases, the nugget size decreases. With the same trend of experimental results of the three kinds of material thickness, we take the experimental results of 1mm thickness in this research to illustrate a correlation on Weibull reliability analysis between welding parameters and tensile shear strength. According to Weibull reliability analysis, all Weibull modulus are larger than 1 with jointing strength of spot welds belonging to wear failure mode. With welding current fixed and minimum life considered, 10cycles of holding time and 100kgf electrode force are the best welding conditions that can forecast ultimate tensile shear strength and they also have the best reliability in Weibull distribution of two parameters. Therefore, the best welding parameters of the 1mm thickness are 17.3kA of welding current, 10cycles of holding time and 100kgf electrode force. According to the same experimental method, the best parameters of 0.8mm thickness are 17.3kA of welding current, 10cycles of holding time and 60kgf electrode force. Further, those of 1.2mm are 17.3kA of welding current, 13cycles of holding time and 100kgf electrode force.