Study On Controlling Of Welding Hot Cracking For Aluminum Alloy By Welding With Transverse Ultrasonic

Contraposing the problems of large welding hot cracking tendency for aluminumalloy sheet, based on the view of mechanics, a new method named welding withtransverse ultrasonic(WWTU) is proposed to control welding hot cracks of aluminumalloy thin-plate weldments in this dissertation. During the welding process, a propertransverse compressive load that is applied in the direction vertical to the weld metalin brittle temperature range (BTR), transverse ultrasonic produces transversecompressive strain which can reduce the transverse tensile stress and strain when theweld metal is contracted during its solidifying, and the mechanical condition ofwelding hot cracking is changed. Then the purpose of controlling welding hotcracking is achieved.According to basic principle of welding with transverse ultrasonic, the designblock diagram of WWTU device was set up and a workable WWTU device thatmeets the experimental requirement well was developed.Both finite element numerical simulation and the welding procedure test areapplied to clarify the mechanism of controlling hot cracking by welding withtransverse ultrasonic. The model of WWTU was established by using MARCsoftware. The temperature field, stress field and strain field of aluminum alloy thinplate under the action of the transverse ultrasonic vibration in the welding process aresimulated. The simulation result has proved the feasibility of the new method and thereliability of the model. Moreover, the simulation results help to establish the properparameter of engineer testing, the location of ultrasonic vibration device and width ofultrasonic vibration action. The results of numerical simulation shows that thetransverse ultrasonic vibration produce transverse compressive plastic strain in BTRmetal, and the plastic deformation was transmited to the weld centre through themetal within BTR. Under the condition of conventional welding, transverse tensilestrain of weld center is3.639%, while the transverse tensile strain reduce to2.274%when welding with50W transverse ultrasonic, and the transverse strain transform into compressive strain with the value of-4.093%when applied welding with150Wtransverse ultrasonic. The result indicates that the transverse ultrasonic can extrusionthe weld metal, and reduce the tendency of hot cracking, the effect is obvious.Experimental verification is carried out on a self-developed equipment. Thefishbone crack test was adopted to investigate the effects of conventional welding andwelding with transverse ultrasonic on hot cracking rate during welding of LY12CZaluminum alloy. The cracking rates of conventional welding compared with that ofwelding with transverse ultrasonic. The experiment results show that with the powerof transverse ultrasonic increasing, the transverse compressive stress reached weldcenter increases gradually, and the cracking length and cracking rate are reduced.When the power of transverse ultrasonic reaches a certain value (150W), the crackingis prevented completely.