Study On Weldability And Welding Processes Of High Strength 7055 Aluminum Alloy By Spray Forming

.Spray forming(SF), as an advanced technique of alloy preparation by rapid solidification,has possessed many significant advantages in high strength aluminum alloys. There are many researches have been carried out on the preparation techniques microstructure,mechanical property and the heat treatment technology, but the subjects on the weldability and welding technology of high strength aluminum alloys prepared by spray forming is seldom, especially in domestic. Building a reasonable weldability assessment norm is a necessary condition for the popularization and application of high strength aluminum alloys prepared by spray forming.Friction stir welding and tungsten inert gas arc welding (TIG) were employed to 4mm 7055 plate prepared by spray forming. Microstructure and mechanical property of the joints were analyzed by OM,XRD,SEM,EDS, etc.Tensile strength of the joint made by TIG using 7055 wire is higher than that of using 4043 wire and 5183 wire. Microstructure analyses show that: Grain size grows in HAZ. A large amount of alloying element was segregated in the grain boundaries, the integrity of the structure was lacerated and the mechanical property deteriorated. XRD analysis show that: The amount ofη(MgZn₂) phase decreased sharply and a great many of T (Al₂Mg₃Zn₃) phase formed. Tensile fracture SEM photographs show that: the fracture appearance of TIG joint was intergranular.Tensile strength of the joint made by FSW increased with theω/νvalue, reach the highest tensile strength 450.8MPa in the parameter of S1000F80, then decreased with the increase of theω/νvalue. The variation trend of hardness across the joint showed the same way with the tensile strength. The FSW joint was composed of Nugget,Thermal Mechanical Affect Zone(TMAZ)and Heat Affect Zone(HAZ). Welding parameters have little impact on the grain size of the HAZ, but the grain size of the TMAZ and Nugget increased with theω/νvalue because of the heat input. XRD analysis shows that:η(MgZn₂) phase was dissolved and reprecipitated in Nugget. Precipitation in TMAZ and HAZ dissolved partly or coarsened. Joint made by FSW in the parameter of S1200F80 show the most obvious characteristics of fracture toughness in accord with the highest Elongation in all the parameters.T6 heat treatment have been employed to the joints which made by TIG using the 7055 wire and FSW in the parameter of S1000F80. The tensile strength of the joint made by TIG increased drastically, but the elongation have little change, Segregation in the weld zone have been eliminated, mixed fracture of intergranular and transgranular was found.Tensile strength and elongation of the FSW joint increased and more obvious characteristics of fracture toughness was obtained after heat treatment.