Microstructural and nanomechanical behavior of friction stir welded dissimilar joint of AA2219-T6/AA2195-T8 alloys

To achieve the new strategy of low cost and outstanding property, friction stir welding (FSW) was used to join AA2219-T6 alloy and AA2195-T8 alloy. The relationship between macro/microstructure and nanomechanical properties was established by using a nanoindentation instrument. During FSW, the grains in stir zone were refined by recrystallization, and the main mechanism of recrystallization was continuous dynamic recrystallization and geometric dynamic recrystallization. The overall micro-hardness value of AA2195 alloy was higher than that of AA2219 alloy due to the strength of the material, and the decrease in hardness value is attributed to the dissolution and coarsening of precipitation. Each zone of the dissimilar joint showed obvious indentation size effect, and the highest nano-hardness values of 2219-base metal (BM) and 2195-BM zones were 1.42 and 1.71 GPa, respectively. The nano-hardness is closely related to the precipitation behavior and follows the same law as the distribution of micro-hardness. The creep mechanism was mainly dislocation slip. The combined action of grain boundary, dislocation, and coarse precipitation can affect creep resistance, in which coarse precipitation plays a dominant role.