Microscopic and Mechanical Properties Characterization of Laser Beam Welded 5754 to 6063 Aluminum Alloys

Laser beam welding (LBW) has been widely employed to acquire defect-free joints between aluminum alloys for a wide range of applications, especially within the automotive industry. The current study aims to examine the effect of laser power on the final microstructure, as well as the mechanical properties of laser beam welded AA5754 and AA6063 aluminum alloys. Lap joints of the abovementioned alloys were performed using a 1030-nm Yb:YAG LBW process with a laser power of 3000 W and 3500 W. The microstructure of base metals (BM), heat-affected zone (HAZ), and fusion zone (FZ) was investigated by means of visible light microscopy (VLM) under non-polarized and polarized light, as well as of scanning electron microscopy (SEM) in conjunction with energy-dispersive spectroscopy (EDS), while the crystal structure was evaluated by X-ray diffraction (XRD). The mechanical properties of welded samples were investigated through Vickers microhardness and tensile shear tests. Furthermore, the fracture surfaces were observed under a stereoscope and a SEM. The metallographic examination revealed the presence of small defects, such as pores, with a diameter ranging from 20 to 50 μm, and microcracks, whose length ranged from 300 to 400 μm. Reducing the laser power was observed to affect the weld geometry, and more specifically the penetration, that was found at 900 μm for the samples welded with 3500 W and 333 μm for those welded with 3000 W. It was also noticed that reducing the laser power resulted in decreased width of the HAZ; the samples welded with 3000 W had a HAZ width of approximately 400–500 μm, while the samples welded with 3500 W had a HAZ width of 500 μm. Finally, applying higher laser power was observed to improve the mechanical properties of welded samples, resulting in higher relative ductility and fewer microhardness fluctuations within the FZ. The specimens welded with 3500 W presented increased tensile shear force and displacement of 3.8 kN in comparison to 3.4 kN of the joints welded with 3000 W.