Nd: YAG laser welding of ZE41A-T5 magnesium sand casting alloy

Butt joints of ZE41A-T5 plates with two thicknesses (2 and 6 mm) were laser welded using 1.6 mm EZ33A-T5 filler wire and a continuous wave Nd:YAG system with variable laser process parameters; power (2.5--4 kW), welding speed (2--7 m/min), joint gap (0--0.6 mm) and defocusing distance (0 to -4 mm). Acceptable weld geometries with smooth top and bottom profiles and minor defects were produced with the open keyhole mode. The optimum laser power was 4 kW for both thicknesses, and the welding speed was 6 and 2 m/min for thin and thick plates, respectively. The suitable gap size for the 2 mm and 6 mm plates was found to be between 0.3 and 0.4 mm. The increase in welding speed reduced the FZ defects on a condition of having an open keyhole mode. The fusion zone showed significant grain refinement due to high cooling rate. No grain coarsening was observed in the HAZ. The microhardness test showed that fusion zone hardness was recovered to the value of the base metal after natural aging of around one year. The HAZ with a typical width between 1.5 and 2 mm, showed a drop in hardness compared with the BM. Tensile test showed that the optimum parameters had a joint efficiency between 85 and 95%. Moderate and high Weibull moduli were obtained for the mechanical properties and weld geometry indicating that the laser welding process seems to have good repeatability. Simulation of laser welding process was developed through combining different models and concepts that enabled to describe the keyhole and weld profile. This model shows good agreement with the experimental results

Reliability of Laser Welding Process for ZE41A-T5 Magnesium Alloy Sand Castings

Laser welding is a promising joining method for magnesium alloys. The process reliability of 2-mm ZE41A-T5 butt joints welded by a 4 kW Nd:YAG laser was investigated from weld geometries, defects and mechanical properties using Weibull statistical distribution. Smooth, geometrically regular and macroscopically defect-free sound joints were obtained. However, sag, undercut, surface misalignment, and some variations in weld width and fusion zone area were also observed. The results indicated that tensile strength and elongation at fracture can be more accurately described by Weibull distribution. The modulus values of 31.98 and 22.52 were obtained for tensile strength in the as-welded and the aged conditions, respectively, indicating that tensile strength becomes more scattered after artificial aging. The aging treatment does not significantly affect mechanical properties, although it can provide stress relief. After laser welding, there is some degradation in tensile properties, especially elongation at fracture. [doi:10.2320/matertrans.MRA2007622