Study On Controlling Of Welding Distortion And Hot Cracking Of Aluminum Alloy By Welding With Two Direction Trailing Ultrasonic

Contraposing the problems of large welding distortion and high susceptibility to hot cracking for hard aluminum alloy sheet, a new method named welding with two direction trailing ultrasonic vibration is proposed. During welding of aluminum alloy sheet applying vertical and transverse ultrasonic excitation to comprehensive control of welding deformation and thermal cracking. Vertical ultrasonic is applid behind a certain distance in high-temperature plastic zone, the metal parts of which is excitated to produce longitudinal plastic flow to offset weld shrinkage, then the welding distortion is controlled. The transverse ultrasound is applid on both sides of the sheet, transverse ultrasonic produces transverse compressive to the brittle temperature range to offset the fracturing transverse tensile strain in the cooling process, then the purpose of controlling welding hot cracking is achieved.The finite element model of welding aluminum alloy sheet with two direction trailing ultrasonic vibration is built using MARC software for the principle of welding with two direction trailing ultrasonic vibration. The simulation value of temperature field and stress field of aluminum alloy thin plate was contrast to measured value to prove the reliability of the model.Some welding parameters were initially identified by simulating,the best vibration power and the scope of effective vibration of vertical ultrasonic for controlling welding distortion were obtained, the correspondence between the excitation amplitude and power of transverse ultrasonic for controlling welding hot cracking are determined.Developing the apparatus and jig for two direction trailing ultrasonic vibration and carrying out the test. The results showed that the vertical ultrasonic play a major role in terms of welding distortion controlling, but it can also increase the welding hot cracking tendency. Transverse ultrasonic can completely inhibit the generation and expansion of welding hot cracking, while there is a certain contribution to welding distortion controlling. The test results show that the effective vertical ultrasonic vibration distance between vibrating position and molten pool is 25mm-50 mm, the maximum deflection deformation tends to decrease with the decreasing of the vertical ultrasonic vibration distance when the transverse ultrasonic power remains 100 W. When the vertical ultrasonic vibration distance is 25 mm, the maximum deflection deformation is 2mm,while the crack rate of the specimen increases. Increasing the transverse ultrasonic power can effectively suppress the generation of welding hot cracking,when the vertical ultrasonic vibration distance is 25 mm,the crack rate is 9.7% with the power of transverse ultrasonic reaches 100 W, there is nearly no macroscopic hot cracking after transverse ultrasonic reaches 200 W.Contrasting microstructure and mechanical properties of LY12 plate welded joints welded under two direction trailing ultrasonic vibration with conventional welding, the result shows that welding with two direction trailing ultrasonic vibration will refine the grain size of fusion zone of welded joint metal, the weld zone metal tends to longitudinal plastic flow. Vickers hardness measurement showed that the hardness of welded joints are greatly improved compared to conventional welding.