In this paper, we investigate acoustic emission properties under static tension of aluminum-magnesium alloys with welded joints produced with a friction stir welding technology. Root mean square (RMS) values of stress rate are used as informative parameters of acoustic emission. Test samples are produced under specific operating conditions with significant deviations from optimal parameters of welding, thus, resulting in structure defects at the welding area and significant differences in processes of plastic deformation, prefracture, and fracture. We reveal significant differences in dependences of acoustic emission informative parameters from welding parameters. It is presented in a set of «RMS of stress rate — strain rate» curves with noticeable change of curves shape. These differences are caused by changes of sources and mechanisms of acoustic emission due to changes of welded joint structure defects. Such effect can be used for defect structure testing. The obtained results can be used as a basis for future development of new acoustic emission techniques and devices for testing of welded joints in aluminum alloys.