Optimization of Process Parameters and Analysis of Microstructure Characteristics of Al/Mg Dissimilar Materials Friction Stir Welding
The microstructure characteristics of 1060 aluminum/AZ31B magnesium dissimilar materials friction stir welded joints were studied by optical microscope and electron backscatter diffraction,and the response surface model was established by Box-Behnken method to optimize the welding process parameters of offset ρ,rotation speed ω and welding speed v.The results show that when the heat input is too high or too low,the aluminum and magnesium materials in the nugget zone are difficult to be fully mixed,and even hole will be generated;the volume of the stirred aluminum and magnesium materials is affected by the offset of stirring pin,when the stirring pin is offsetted,the volume of aluminum and magnesium materials is uneven,which will also lead to insufficient mixing of aluminum and magnesium in the nugget area.By analyzing the response surface model,it is found that the welding speed has the greatest influence on the tensile strength of the joint,and the optimal process parameters are ρ=0 mm,ω= 1200 r/min,v=150 mm/min,and the tensile strength of the joint is high,the prediction value reaches 95.7 MPa.Under the welding process parameters,the nugget zone of the joint has no defects and the materials are fully mixed,and the microstructure presents good mechanical interlocking characteristics.Due to dynamic recrystallization in the nugget zone,uniform and fine microstructure is obtained.The measured tensile strength of the joint is 96.1 MPa,which is basically consistent with the predicted value of response surface model.
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