Small Creep Deformations and Residual Stress Relaxation in Welded and Shot Peened Al Mg Si Cu-aluminum Alloys

The stability of compressive residual stresses and the stability of strain hardening states are seen to have high technical importance. For a laser beam welded AlMgSiCu-alloy, results of applied stress and residual stress relaxation at elevated temperatures 100100°C, and only small differences between welding zones and base material occur. Shot peening induced residual stresses decrease to a large extent in the weld seam areas yet remain stable to a higher extent in the base material after stress relaxation tests (and also after creep tests, low cycle alternating thermal or thermal mechanical tests). Calculations of residual stress relaxation based on applied stress relaxation tests underestimates the relaxation behavior due to the different nature of applied stresses and residual stresses and the higher relaxation of surface residual stresses. INTRODUCTION Precipitation-hardened wrought Aluminum alloys are construction materials for the automotive and aircraft industries. The copper alloyed AA6056 is used for its high corrosion resistance, good weldability, high strength as well as high damage tolerance [1]. Laser beam welding of this alloy causes characteristic microstructures and inferior mechanical properties in the weld seam [2, 3]. Surface treatments such as shot peening are appropriate methods to increase the fatigue strength of these welded materials [4]. It is well known, that residual stresses at the surface and/or in surface layers determine the fatigue and corrosion resistance. . However there is a lack of knowledge about the long-term stability of induced residual stresses and strain hardening states regarding complex superimpositions of cyclic thermal and mechanical service conditions. Service temperatures can be as high as around 80-100 °C, the onset of creep deformation in AlMgSi-Aluminum Alloys. The relaxation behavior of applied stresses and residual stresses was examined for the base material and welded and shot peened conditions at temperatures from 100°C to 150°C. 477 Copyright ©JCPDS-International Centre for Diffraction Data 2009 ISSN 1097-0002