Mechanisms of the porosity formation during the fiber laser lap welding of Al 5754 sheets

The aluminum alloys has been increasingly used in the automotive industry in order to reduce the vehicles” weight and improve the fuel efficiency. When joining the aluminum alloys, one of the big challenges is the formation of porosity, which deteriorates the mechanical properties of welds. In this study, the lap welding was conducted on an aluminum alloy 5754 metal sheets with a thickness of 2 mm. The effects of various laser welding parameters on the weld quality were investigated. The porosity content was measured by X-ray inspections. A porosity-free weld was achieved even in the condition of partial penetration. The key is to control the solidification duration of molten pool. When the solidification duration of molten pool is large enough, more bubbles can escape from the molten pool and less or even none remain as porosity.