在不同的搅拌头转速及焊接速度下, 对2 mm厚AlCuLi合金进行了搅拌摩擦焊接. 结果表明, 焊核区由细小等轴再结晶晶粒组成. 随搅拌头转速增加, 晶粒尺寸逐渐增加; 随焊接速度增加, 晶粒尺寸略有减小. TEM分析表明, 焊核区的析出相大部分溶解, 在随后的冷却过程中形成粗大的析出相, 而在热影响区析出大量的粗大平衡相. 在较低的焊接速度(80 mm/min)下, 接头在热影响区的硬度最低点发生断裂, 随搅拌头转速增加, 接头强度逐渐升高, 最高可达母材的87%, 延伸率约为10%. 而在较高的焊接速度(200 mm/min)下, 搅拌头转速较低时, 焊核区材料流动不充分, 样品在焊核处发生断裂, 强度较低, SEM分析表明, 断口出现材料流动不充分导致的缺陷; 随搅拌头转速增加, 断口处缺陷明显减少, 对强度影响不显著, 接头强度可达母材的84%.
Friction stir welding (FSW) of a novel AlCuLi alloy was conducted to investigate the effect of welding parameters on the microstructure and mechanical properties of the joints. The fine and equiaxed dynamically rotation rate increased, the size of the grains in the NZ increased. However, with increasing the welding speed, the size of the grains in the NZ decreased slightly. TEM analyses indicated that most of the precipitates in the NZ dissolved into the matrix during FSW and some coarse precipitates formed during subsequent cooling process. Moreover, many coarse precipitates were observed in the heat affected zone (HAZ) due to the FSW thermal cycle. At a low welding speed of 80 mm/min, the ultimate tensile strength of the joints increased as the rotation rate increased, and could reach up to 442 MPa which was 87% of that of the base metal. All of the joints failed in the lowest hardness zone of the HAZ. At a high welding speed of 200 mm/min, some defects resulting from insufficient material flow were observed on the fracture surfaces. At a low rotation rate, the joints failed along the defects in the NZ and exhibited a low strength. As the rotation rate increased, the size and number of the defects decreased. Therefore, the effect of the defects on the strength of the joints was significantly reduced, and a joint efficiency of 84% was obtained.
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