AbstractIn aircraft construction, T-joints between aluminium alloys are manufactured either by riveting or by two-sided laser beam welding. This article describes one-sided Nd:YAG laser beam welding as a method of manufacturing skin/clip joints between the AA6156-T4/AA6013-T6 and AA2139-T3/ AA6013-T6 aluminium material combinations in T-joint designs. One fundamental problem associated with this procedure is the high porosity level in T-joints executed by means of one-sided laser beam welding. It is shown that the formation of pores is determined not only by the types of the aluminium alloys, the variations in the welding directions and the preparation of the joining faces but also by an excessive angle of incidence between the laser beam and the skin field. The laser beam must be transmitted in the bonding region between the clip and the skin field in order to reduce the porosity level by decreasing the angle of incidence.