Research On Ultrasonic Assisted GMAW Process Of Aluminum Alloy

Aluminum alloys have good processing properties,corrosion resistance,electrical and thermal conductivity and high specific strength,and are now being used more and more widely in rail transportation,automotive structures and aerospace applications.Aluminum alloy is currently more commonly used welding methods include stir friction welding and gas tungsten arc welding(GTAW)and gas metal arc welding(GMAW).In a comprehensive comparison,GMAW process is an important welding method for aluminum alloy due to its advantages of high automation,fast cladding speed,high welding efficiency and low welding cost.However,aluminum alloys are prone to burn-through and under-couch defects,high weld porosity and poor weld seam formation during the welding process of GMAW,which limits the further application of this method.In this project,the transverse ultrasonic vibration is directly applied to the welding torch through the self-designed torch fixture,and ultrasound is introduced into the welding process by causing transverse ultrasonic vibration of the welding wire to achieve ultrasonic assisted molten electrode gas shielded welding and improve the stability of the welding process and weld seam formation.Single-pass overlay welding experiments with different process parameters of MIG and CMT were conducted on 2mm and 6mm thick flat plates.The process image and electrical parameter synchronization acquisition system was used to collect arc and droplet transition images and electrical parameter waveforms to analyze the effect of transverse mechanical ultrasonic vibration on arc and droplet transition.The effect of transverse ultrasonic on weld surface formation,weld porosity and organization was analyzed by optical microscopy.The results of the study show that the effect of transverse mechanical ultrasound vibration on the arc and droplet transition under self-designed conditions is investigated.The results show that the transverse mechanical ultrasound introduced by the self-designed torch fixture has a significant compression effect on the arc root,which makes the arc energy more concentrated and improves the stiffness and stability.With the increase of wire feeding speed,the degree of arc compression first increases and then decreases,and the maximum size of the arc shrinks the most at the wire feeding speed of 7m/min,which can reach 35%.Secondly,the effect of ultrasonic vibration on the droplet transition behavior is more obvious,the effect of ultrasonic vibration varies with different welding parameters.In the MIG welding short-circuit transition parameters,the wire feed speed of 5m/min and 5.5m/min,ultrasonic vibration makes the arc ignition time increases,the droplet size becomes larger,the transition frequency decreases;in the wire feed speed of 5.5m/min,the droplet transition frequency is reduced by 45%,Because lateral ultrasonic vibration suppresses the up and down fluctuations of the melt pool,despite the reduced frequency of the short-circuit transition,the uniformity and regularity of the transition period,short-circuit time and arc-burning time are significantly improved,and the stability of the droplet transition and welding process is significantly improved.Within the parameters of the MIG welding hybrid transition,transverse mechanical ultrasonic vibration promotes the molten drop from the wire,the short-circuit transition basically disappears,the molten drop transition mode into a more stable shot drop transition.When in the MIG welding shot drop transition parameter range,under the action of ultrasonic vibration,the molten drop transition cycle is shortened,the transition frequency becomes faster,at the wire feed speed of 7.5m/min,the molten drop transition frequency increased by 8%.For CMT welding,ultrasonic vibration promoted droplet transition.At a wire feed speed of 4.5 m/min,the drop transition frequency increased by 14%.At a wire feed speed of 5.5 m/min,ultrasonic vibration suppressed the abnormal arcing during the short circuit,significantly reduced the extra-long transition cycle,and improved the stability of the drop transition.In addition,under the effect of transverse ultrasonic vibration,the base current duration and short circuit time were significantly reduced,the percentage of peak current phase in the whole CMT cycle was increased,and the actual wire feeding speed was improved.Transverse mechanical ultrasonic vibration on the weld surface formation has a significant improvement effect,the weld surface of the fish scale pattern more dense,the bending and unevenness of the weld channel is significantly suppressed,especially in the MIG welding mixed transition zone process parameters welding weld formation significantly improved,the spatter particles around the weld channel is significantly reduced.In addition,due to the transverse mechanical ultrasound makes the arc energy concentration,thus making the weld depth of melt increased,MIG welding wire feeding speed of 5m/min,the depth of melt increased by 39%;CMT welding wire feeding speed of 4.5m/min,2mm thick workpiece depth of melt 1.36mm,after the application of transverse ultrasonic vibration workpiece weld through.Ultrasonic vibration has a significant effect on the suppression of weld porosity,and at a wire feed speed of 6.5 m/min,the number of porosity in the unit area of the weld is reduced by up to 52%.In addition,under the action of ultrasound,the location distribution pattern of pores in the weld underwent significant changes.The percentage of pores at the top of the weld(residual height area)increased significantly,and the percentage of pores with size over 120 μm increased.The columnar grains in the middle of the weld were refined under the effect of ultrasonic cavitation,and the columnar grain area at the bottom became narrower or even disappeared.