WELDING AND WELDABILITY STUDIES ON 2195 AL-CU-LI ALLOY


ABSTRACT

In this work, the solidification cracking behavior of 2195 Al-Cu-Li was investigated, and the susceptibility was compared with conventional alloys viz., 2219, and 2014. Varestraint test, Gleeble® hot ductility test, and Thermo-Calc® simulation were conducted to rank these alloys based on crack susceptibility. 2195 alloy showed the highest cracking sensitivity, whereas 2219 alloy exhibited the least susceptibility in all three weldability techniques.
Hot cracking criteria have been successful in grading the crack susceptibility of an alloy, but they do not offer a safe window of parameters for a crack-free weld. This work intends to determine the processing window for crack-free welding using a high throughput experiment coupled with computer simulation. An experimental setup to produce a spiral welding path was developed to obtain a wide variation in heat input resulting in a range of cooling rates (Ṫ) and temperature gradients (G) in a single experiment. Simulations using OpenFOAM®️ were performed to determine the spatial variation in Ṫ and G. A parametric space constructed using cooling rate and thermal gradient extracted from various points along the spiral path was used to map the regime for a crack-free weld. The results were rationalized using microstructure evolution and microsegregation predicted using phase-field simulations.
The effect of filler wire (2319 and 4043) on mechanical properties and microstructural evolution in 2195 gas tungsten arc welds (GTAW) was studied. Considering the limited weldability of 2195 alloy by the fusion welding process, friction stir welding (FSW) was performed to improve weld properties and eliminate the fusion welding-related defects. The effect of FSW process parameters on mechanical properties and microstructure of 2195 welds were studied. The optimum parameters to achieve defect-free welds were identified, with a maximum weld efficiency of 73 % in the as-welded condition. Tensile properties of FSW welds at room temperature and cryogenic temperatures (77K and 20K) were evaluated. Local micro tensile properties and microstructural changes at various zones of FSW welds were investigated.
Due to through-thickness anisotropy in 2195 alloy, it is not preferred to be used in thicker sections of aerospace components. In contrast, 2219 possesses good isotropic properties in the thick sections. Therefore, dissimilar FSW joints of 2195-2219 are envisaged. The effect of material position at the advancing side (AS) and retreating side (RS) was investigated. The strength of dissimilar joints depended on the material with lower strength rather than the position of the material. However, placing the low-strength material in RS led to higher joint strength. The location of failure was always in the TMAZ of welds. The electrochemical corrosion and stress corrosion cracking (SCC) resistance of the 2195-2219 dissimilar FSW joints were investigated and compared with similar joints of 2195 and 2219. In 2195-2219 dissimilar joints, the TMAZ of 2219 showed the highest corrosion rate, and the stir zone exhibited the lowest corrosion rate. The slow strain rate test (SSRT) confirmed that the dissimilar joints possess good resistance against stress corrosion cracking.

Keywords: 2195 alloy, weld solidification cracking, high throughput experiment, friction stir welding.