The mechanical behavior of both, reference and electron beam welded aluminum alloy 6156 specimens was experimentally investigated. Sheets of AA6156 were artificially aged before and after the welding process and tensile specimens were machined from the welded sheets according to the ASTM E8 standard. The specimens were artificially aged at 170 ^° C for different times that corresponded to all precipitation-hardening conditions, namely under-ageing (UA), peak-ageing (PA) and over-ageing (OA). The results showed that the effect of welding without any heat treatment (condition T4) decreases by, about 100 MPa, the yield stress and the yield strength, while the remaining elongation at fracture hardly exceeds 4 %. It was also shown that artificial ageing before welding increases the tensile ductility (almost 50 % joint efficiency in deformation) while the artificial ageing post to welding significantly increases the strength properties (more than 75 % joint efficiency in strength).