| As an important part of SF6 Gas-Insulated Switchgear(GIS),the canted-coil-spring contact element can be made independently in China now.But the tensile strength of domestic canted-coil-spring solder joints is lower than that of foreign products,and the quality has fluctuation.This paper studies on the factors that affect the strength of the solder joint of CuCo2Be canted-coil-spring,and improves the process parameters in the manufacturing process.In this paper,the samples of solder joints formed under different drawing processing rates,welding processes and heat treatment processes are designed respectively to study the influence of these parameters on the structure and strength of solder joints.The microstructure and age precipitates of the weld were examined and analyzed by metallographic microscope and field emission scanning electron microscope.The hardness of the weld was analyzed by micro Vickers hardness tester,and the tensile strength was measured by tension compression tester.The results show that after aging treatment,the peak strength of base metal and weld spot increases with the increase of drawing processing rate.The welding parameter is the direct factor of the quality of the welding spot.If the input heat is too large or too small,the strength of the solder joint is unqualified.When the welding heat is too large,the solder joint is concave,the pores in the fusion zone become more,and the tensile strength decreases.The weld area is dendrite morphology,and the original casting compound disappears.The microstructure of the heat affected zone is equiaxed crystal formed by heat recrystallization.After heat treatment,the hardness of the weld area is higher than that of the base metal,and the hardness of the heat treatment area is slightly lower than that of the base metal.In the tensile test,most of the qualified solder joints are disconnected from the heat affected zone.Compared with TIG welding,the weld area and heat affected area of laser welding are smaller and the tensile data is more stable.It is shown that the process of strength change of solder joint is not identical with that of base metal during aging treatment.The strengthening rate of solder joint is higher than that of base metal when the temperature is lower than the peak temperature.In peak aging treatment,the strengthening rate of base metal is higher than that of solder joint.When the aging temperature is too high,the grain boundary coarsens obviously,the strength of the solder joint and the base metal begins to decline rapidly,and the strength gap and data volatility also become smaller.For the tensile strength of base metal and solder joint,the extension of aging time will lead to a slight decrease in strength,but it can improve the stability of tensile results and narrow the gap between base metal and solder joint.When the temperature is extended to 10 hours,there is no obvious change of grain boundary.With the increase of solution process and aging treatment after welding,the properties of solder joints can be increased slightly.However,the solid solution process is difficult to control and there is a risk of overheating. |
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