[[alternative]]A Study on the Nugget Forming and the Reliability Analysis of Joining Strength for 1050-O Pure Aluminum by Resistance Spot Welding

[[abstract]]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.