Effect Of Space Thermal Cycling And Radiation Environment On The Microstructures And Properties Of Welded LF6 Aluminum Alloy

In this paper, the LF6 aluminum alloy variable polarity plasma arc welded (VPPAW) joints and welded plates were taken as the objects for study. The author investigated the performance changes of the LF6 aluminum alloy welded samples under the terrestrial space thermal cycling and irradiation environments using the physical simulation methods. The mechanisms of the performance changes of the welded samples were also investigated by the mesostructure and microstructure analysis. The determination and analog computation of the welding residual stress were carried out by both experimental and finite element calculation methods. The distribution of welding residual stresses of the welded plates under different butt joint parameters were achieved.It is found that VPPA welding process may introduce many particles in the joint area especially in the heat affected zone. The thermal mismatch stress may be caused between the matrix and the particles under the temperature variation conditions. The thermal mismatch stress coupled with external stress lead to the interface debonding between the particles and matrix, therefore form the microvoids inside the materials in the welded joint area (primarily in the heat affected zone which contains more bulky second phase particles ) after the long period of thermal cycle conditions. The formation and evolution of the microvoids may decrease the load-carrying ability of the welded joints. After the terrestrial space irradiation test, the welding longitudinal residual stresses of the welded plates increased,the tensile strength and yield strength of welded joints also increased, however their plastic strain decreased. A plenty of dislocation loops and lines in observation areas of welded samples emerged, and the dislocation density in these areas increased. The simulation results of the welding residual stresses of the welded plates show that the butt welding parameters have greater impact on the joints with unfitness type than that of the joint with interval type. The results of prediction and actual measured were compared and the results coincided with each. other.