Porthole die extrusion is an always more important process for industrial applications. It is, however, characterized by a considerable complexity; in fact, different parameters have to be carefully set for improving the final part. A critical zone that strongly influences the goodness of the extruded component is the so called “welding plane”. It is the junction area where material flows converge inside the welding chamber. The variables that have to be controlled for improving the material characteristics in this zone are the effective stress, the pressure and the time that the material takes to cross the welding chamber. Moreover, material temperature is another fundamental issue that influences both the quality and the typology of the final joint. However, especially for complex parts, the material can follow diverse directions to get out from the die; this means that the deformation history can be different, thus influencing the quality of the final jont. In the study here proposed, the property of the welding plane was highlighted for an industrial component that was cut through a profile cross section carrying out both metallurgical and mechanical investigations. More in detail, specimens, derived from the extruded part, were mounted, polished and etched with Keller reagent and observed by a light microscopy. Then, macro and micro observation were developed highlighting the welding line position. Moreover, local values of the average grain size of the material were measured showing the microstructural evolutions undergone by the material due to the extrusion process. As far as mechanical tests are regarded, micro-hardness tests were executed nearby the welding line; in this way, correlations between material metallurgical evolutions and subsequent local mechanical performances were highlighted. Furthermore, a 3D numerical study was developed in order to point out the numerical ability to predict the welding line position for complex parts; finally, a welding criterion was used in order to locally validate the experimental observations. All these aspects are accurately analyzed and discussed in the paper.