Xiyuan Hu

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.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.

Porosity mechanism of fiber laser welding with filler wire for aluminum alloy

The mechanism of porosity formation and its suppression methods in laser welding with wire filler have been studied by using a 4 kW fiber laser to weld 5A06 aluminum alloy with SAl-Mg5 filler. It is found that the porosity formation is closely related to the stability of the keyhole and fluctuation of the molten pool in laser welding aluminum alloy. The filling wire increases the instability of the keyhole and weld pool, therefore, further increases the amount of porosities in the joint. Prefabrication a suitable gap for the butt joint can provide a natural passage for the flow of the liquid metal, which can weaken and even completely eliminate the disturbance of the filling wire to the formation of keyhole. And the gap can also provide a passage for the escape of the bubble. So, this method can greatly decrease the susceptibility of the porosity. Moreover, for a thin sheet, if the power of laser is sufficient to form a keyhole with stable penetration through the weld sheet, a weld bead without gas cavity can also be obtained because the closeness of the keyhole is almost impossible.The mechanism of porosity formation and its suppression methods in laser welding with wire filler have been studied by using a 4 kW fiber laser to weld 5A06 aluminum alloy with SAl-Mg5 filler. It is found that the porosity formation is closely related to the stability of the keyhole and fluctuation of the molten pool in laser welding aluminum alloy. The filling wire increases the instability of the keyhole and weld pool, therefore, further increases the amount of porosities in the joint. Prefabrication a suitable gap for the butt joint can provide a natural passage for the flow of the liquid metal, which can weaken and even completely eliminate the disturbance of the filling wire to the formation of keyhole. And the gap can also provide a passage for the escape of the bubble. So, this method can greatly decrease the susceptibility of the porosity. Moreover, for a thin sheet, if the power of laser is sufficient to form a keyhole with stable penetration through the weld sheet, a weld bead without gas cavity...

Study on periodical oscillation of plasma/vapor induced in high power fibre laser penetration welding

High power fibre laser has been receiving attention because of advantages such as high output power, high beam quality and flexible fibre delivery. Studies on mechanism of fibre laser welding will further promote its practical application. In this paper, high speed video observation was used to study the characterization of plasma/vapor induced during bead on plate welding of ZL114 with high power CW fibre laser and to analysis the reason for periodical oscillation of the plasma/vapor. The results show that plasma/vapor induced with high power laser is oscillated periodically at 450-600 µs cycle above the weld pool surface. Shielding gas has little effect on the oscillation cycle. The main reason for periodical oscillation of the plasma/vapor is the oscillation of the keyhole and the weld pool.High power fibre laser has been receiving attention because of advantages such as high output power, high beam quality and flexible fibre delivery. Studies on mechanism of fibre laser welding will further promote its practical application. In this paper, high speed video observation was used to study the characterization of plasma/vapor induced during bead on plate welding of ZL114 with high power CW fibre laser and to analysis the reason for periodical oscillation of the plasma/vapor. The results show that plasma/vapor induced with high power laser is oscillated periodically at 450-600 µs cycle above the weld pool surface. Shielding gas has little effect on the oscillation cycle. The main reason for periodical oscillation of the plasma/vapor is the oscillation of the keyhole and the weld pool.