Strength Of Copper Joints Obtained By Ultrasonic Welding Using Copper Intermediate Layers In Different Structure States

Characteristics of solid state joints obtained by ultrasonic welding (USW) of commercially pure copper plate samples of 0.5 mm thickness, including samples welded with intermediate layers of commercial and ultrafine-grained (UFG) plates of the same material of 0.2 mm thickness, were studied. Welding regimes with processing times 1 and 2 s and static loads 5 and 7 kN at vibration amplitude about 15 mu m were used. For each regime and sample type three samples were obtained and subjected to lap shear testing. Analysis of results has shown that at both values of static load the increase in processing time from 1 to 2 s leads to an increase of the strength of weld joints. While with the small welding duration the increase in the load does not lead to a change of the joint strength, with the longer welding time 2 s a noticeable increase of the joint strength with the static load is observed. For the given thickness of intermediate layers lap shear strength of joint does not depend on their presence and structure: for every sample type welded with the same regime the value of strength is the same within the margin of errors. However, presence of the intermediate layer qualitatively affects the elongation curve during shear testing: samples welded without an intermediate layer fail with practically instant simultaneous separation of joined surfaces after achievement of the maximum stress, whereas at the presence of an intermediate layer after achieving the maximum stress a smooth decrease of the stress occurs. This is related to the deformation of material in the area of joint. There are also differences observed in the macrostructure of sample surfaces in the area of failure after lap shear testing. The absence of the increase of joint strength in the presence of intermediate layers was explained by plastic deformation in the areas of stress concentration.