INFLUENCE OF FRICTION STIR WELDING PARAMETERS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AA2024-T3 ALUMINUM ALLOY

摘要

In this study. 3mm thick AA 2024-T3 Aluminum alloy plates were friction stir butt welded. Effects of welding parameters such as rotation speeds (6.67-25 sec~(-1)), welding speeds (0.83, 1.67 mm/sec) and backing plates on microstructures, hardness distributions, and tensile properties of the joints were investigated. Three types of backing materials were used, including stainless steel, copper block, and a combination of the two. Orientation distributions in the weld zone were investigated using electron backscatter diffraction patterns (EBSP). The grain size in the stir zone (SZ) increased with increasing rotation speed and decreased from 7.4μm with stainless steel to 4.4 and 1.7 μm with a combination backing type and copper-block, respectively. The orientation distribution changes gradually in the SZ, suggesting a complicated metal flow during FSW. Hardness increased both in the SZ and the thermo- mechanically affected zone (TMAZ) as the rotation speed increased. A hardness maximum appeared in heat affected zone (HAZ) for a higher welding speed and when using a combination of stainless steel and copper block plate (backing type 3). The tensile strength of the joints increased with increasing rotation speed and a maximum value of 427MPa was achieved with type 3 backing plate.