High cycle fatigue behaviour of thin sheet joints of aluminium-lithium alloys under constant and variable amplitude loading

The main purpose of this work is to establish high cyclic fatigue behaviour of sound welds of aluminium alloys of Al-Mg-Li and Al-Cu-Li doping system under constant and variable amplitude loading. Sound welds of thin sheet (1.8 and 2.0 mm) aluminium-lithium alloys 1420 and 1460 were produced by tungsten inert gas (TIG) and friction stir welding (FSW) technologies. Microstructure investigations, hardness and residual stress measurements, tensile and fatigue tests of welds were performed. It is shown that FSW joints have fine grain microstructure in weld nugget with homogeneous disoriented structure and elongation and deviation of grains in a direction of plasticized metal movement, taken place in adjacent areas. Hardness on joints face was measured, showing areas of softening near the weld. Lower temperature of welded edges heating reduces the maximum level of longitudinal residual tensile stresses in FSW joints in comparison with TIG welds. Tensile strengths of TIG and FSW joints were obtained. The high cycle fatigue tests of FSW and TIG joints under constant and variable amplitude loading were performed. It is shown that fatigue behaviour of FSW joints exceeds the characteristics of the joints obtained by TIG welding.