With the objectives of assessing the mechanical properties such as strength and elongation of a laser weld and clarifying the influence of porosity on tensile properties, this study was performed by observing in-situ deforming and fracturing behavior of a laser-welded A5182 joint during testing through special TV inspection system using microfocused X-ray beams in two perpendicular directions, and CT images. The effect of porosity on mechanical properties was also confirmed by tensile experiments of sheet specimens with artificially drilled holes of different sizes and spaces and by FEM analysis of strain or stress distribution near and between holes.
According to the in-site observation during tensile testing, a specimen was elongated and deformed gradually, and thereafter fracturing was initiated at the side of a large pore and then propagated around it. It was revealed that large pores exerted a great influence on the reduction in strength and elongation but small ones hardly affected the tensile properties. CT image results suggested that the tensile properties were reduced predominantly by a decrease in cross-sectional area of a tensile specimen due to pore formation or an increase in actual (concentrated) stress, and slightly by mutual interaction between pores or pore to the surface. Such mechanical properties could be interpreted by considering hardness or strength profiles of a weld as well as the size and distribution of pores, near which strains and stresses were concentrated.