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The instability of the keyhole and bubble being captured by solidification interface are the main factors that affect the formation of porosity in laser welding of both aluminum alloy and steel. In laser welding of aluminum alloy, the more violent fluid flow behind the keyhole, the larger depth to width ratio can cause the keyhole more unstable, and susceptive to collapse that can be described as three necessary steps. The much larger solidification rate and longer escaping distance make the bubble easily captured by the solidification interface, and easily combined. All of these reasons contribute to the formation of larger number and size of porosity in laser welding of aluminum alloy. The numerical and experimental results are in good agreement. [ABSTRACT FROM AUTHOR]

Carbon-steel filler wire was used to solve the coating problem in laser welded blanks of Al-Si-coated 22MnB5 without a decoating procedure. The effect of the filler wire on the fusion-zone microstructure and mechanical properties was investigated. The Al content was diluted by the filler wire. The δ-ferrite phase was also reduced after the reduction in Al and homogenization. The joint strength was ∼1210 MPa, and the elongation was 1.1% without filler wire. When filler wire was used, the joint strength increased to ∼1550 MPa, and the elongation was greater than 3%. The fracture surface of the joint with the filler wire was ductile. The effects of welding speed and feeding speed were also studied. A reduction in the Al content at the higher feeding speed or the use of a slower welding speed was found to be most effective because either approach enabled more filler material to be added to lower the ratio of the Al-Si coating in the fusion zone. In the absence of the filler wire, the δ-ferrite phases were large and long, connecting to a bulk zone. When the filler wire was used, the δ-ferrite phases were broken up and became narrow and small with a uniform distribution in the martensite matrix. [ABSTRACT FROM AUTHOR]

After N 2 was added into shielding gas, nitrogen content was increased at upper section and central section of laser weld metal. When shielding gas was pure nitrogen, the microstructure of weld cross-section tended to be homogeneous, its corresponding austenite content was over 40%. The formation of allotriomorphic and penniform austenite was promoted remarkably. The shielding gas of nitrogen was helpful to enhance the corrosion resistance of weldment in 3.5 wt.% sodium chloride (NaCl) solution. [ABSTRACT FROM AUTHOR]

This paper concerns the dynamic variation in plume velocity and keyhole size during the laser welding process of 5083 Al-alloy. The keyhole size and plume velocity were measured from high-speed images through imaging process methods and the particle image velocimetry (PIV) method. The correlation between the oscillation in plume velocity and keyhole size was discussed based on the pressure balance inside the keyhole. Results show that the keyhole keeps opening and collapsing during the welding process. During the time the keyhole is open, the size of the keyhole continuously oscillates until it collapses. Plume velocity increases to a maximum at the initial stage of keyhole's opening, and then varies in synchronisation with the oscillation of the keyhole size. It is considered that local evaporation occurs on the humps of the keyhole front wall, which results in the oscillation in plume velocity. The oscillation in plume velocity then leads to the variation in the pressure balance in the keyhole and drives the keyhole to expand or shrink accordingly. [ABSTRACT FROM AUTHOR]