Tensile Fracture in Laser Welding Joints of Al-Cu-Li-Mg-X Alloy Bearing Gaseous Porosity

This article measures the impact of gaseous porosity on the mechanical performance of the laser welded thin sheet of an aerospace-grade Al-Cu-Li-Mg-X material. The laser fabricated joints were characterized by optical microscopy and scanning electron microscopy to reveal the metallurgical features. A uniaxial tensile test was carried out to measure the mechanical strength of the porosity free welds, and porosity bearing welds. The results showed that the welds bearing gaseous porosity performed nearly 24% lower mechanically than the porosity free welds. Fractography exposed the presence of fine spherical holes in porosity bearing welds, which acted as crack nucleation sites, and their further growth lead to a sudden failure at higher strain rates. Microstructural observations revealed that the laser processing has transformed the superior age-hardened microstructure of the base metal into a new as-cast microstructure. The freshly evolved microstructure was held responsible for the low mechanical properties of the joints with respect to the base metal.