Factors controlling keyhole-induced porosity in cold wire laser welded aluminum

Production of lightweight laser-welded assemblies to meet the requirements for higher performance and reduction of carbon emission requires substantial effort in mitigating the effects of processing on welding defects. The factors controlling keyhole-induced porosity during cold wire laser welding of AA6061-T6 were studied. The laser beam intensity distribution parameters and the laser energy deposited per unit length of the weld determine the keyhole behavior, the shape and size of the surrounding molten material and, consequently, the percentage of porosity and average size of pores that resulted from keyhole collapse during welding. Changes in keyhole size and porosity are not noticeably significant with respect to the rate of feeding the cold wire into the molten weld pool. The vapor plume that forms above the molten pool due to the ejection of evaporated metal particles from the keyhole effectively attenuates the laser beam and reduces the depth of penetration. However, the erratic behavior of the plume results in an inconsistent porosity response. The use of a gas jet for deflecting the plume is beneficial for more consistent porosity response. Results from this work provide guiding principles for the selection of process variables for keyhole-mode laser welding of aluminum alloys, depending on the particular application and the criteria for acceptable level of defects.