Study On The Formation And Porosity Of5754Aluminum Alloy By Laser Lap Welding With Filler Wire

Laser welding has been a hot spot of aluminum welding study, which has advantagesof high welding quality, high accuracy, small distortion of weldment, high efficiency andno need of vacuum condition. Except for the advantages of laser autogenous welding,laser welding with filler wire has not only overcome some problem of laser autogenouswelding such as the high accuracy requirement of weldment processing and clamping, butalso been able to adjust welding component and add the metallic element loss. However,the filler wire makes the welding process complex and there are few researches ofaluminum laser welding with filler wire inland. This study used an advanced fiber laserand a welding machine with stable feeding ability to research the weldability of5754aluminum laser lap welding with filler wire.Welding speed had big effect on the weld shape quality. Bad weld shape was gotwhen the welding speed was too high or too low. However, the weld shape quality hadhigh tolerability of the laser power and wire feed rate. Good weld shape was got when thelaser power and wire feed rate were changed during a big range. When wire feed rateincreased, the bead width changed little and the bead tall increased. Otherwise, laserpower and welding speed had a linear relation with the bead penetration. Adding laserpower or decreasing welding speed, the bead penetration increased linearly. Adding wirefeed rate, the bead penetration decreased in ladder form.5754aluminum alloy is a kind of Al-Mg series eutectic alloy with α and β two-phase.The β phase is Mg2Al3compound. Typical weld of5754aluminum alloy laser welding canbe divided into base material zone, heat affected zone (HAZ) and weld zone. Thehorizontal hardness from big to small is weld zone, base material zone and HAZ. Thelongitudinal hardness of weld zone changes little. Because of the high welding speed, theHAZ of laser welding is very narrow. However the microstructure in HAZ is coarser andthe mechanical property is the worst. The microstructure of the weld zone from top tobottom is different. The growth time of top crystal is longer and there is coarser α phasegenerating. The bottom branch crystal and eutectic organization is evenly distributed. Technology pore in the bead has bad influence on the bead property. In laserpenetration welding, some part of metal vapor traps into bubbles due to the mechanicaldisturbance of the key hole. Then the bubbles transform into technology pores when thewelding bead solidifies. When laser power and welding speed change, the temperaturedistribution in the weld pool also changes and this affects the stability of the key hole. Thestudy found that increasing the welding speed can decrease the porosity rate andincreasing the laser power can add the porosity rate. The change of the wire feed ratewithin a certain range had little effect on the porosity rate.At last, based on the research above, how to set a proper gap in the lap bead in orderto decrease the porosity rate was studied. The research found that prefabrication of aproper gap was beneficial to decrease the porosity rate. Under a proper gap, the bubblesforming in the weld pool escaped from the bead and this decreased the porosity rate. Atthe same time, the shear stress was improved.