采用超音速微粒轰击(SFPB)和表面机械滚压处理(SMRT)相结合的混合表面纳米化(HSNC)方法在2A14铝合金表面制备出梯度纳米结构(GNS)表层,之后进行了搅拌摩擦焊(FSW)。利用OM、SEM和TEM对比研究了HSNC样品和原始样品FSW焊缝的微观组织和断裂形貌。结果表明,GNS表层以类似“S”线复杂形式分布在HSNC样品的热机影响区(TMAZ)和焊核区(NZ)中,形成了纳米层区(NLZ);原始样品显微硬度最低处和断裂位置均发生在前进侧的TMAZ,HSNC样品显微硬度最低处和断裂位置均发生在NZ;HSNC样品的抗拉强度比原始样品提高了6.4%,延伸率比原始样品提高了14.1%,两者的断裂方式均为韧性断裂,但原始样品断口形貌为非等轴韧窝和撕裂韧窝,HSNC样品断口形貌为等轴韧窝。分析表明,由于纳米晶的优异性能,NLZ在提高焊缝强度的同时提高了塑性变形能力。
2A14 aluminum alloy is the important raw materials of aerospace, which belongs to the heat treatment aluminum alloy. Friction stir welding (FSW) can weld aluminum alloy with high quality, and can avoid the pores and cracks of fusion welding effectively. In order to obtain better mechanical properties of FSW joints, the surface nanocrystallization method is introduced into FSW technology. By means of the hybrid surface nanocrystallization (HSNC) method of both supersonic fine particles bombarding (SFPB) and surface mechanical rolling treatment (SMRT), a smooth gradient nanostructured (GNS) layer was formed on the surface of 2A14 aluminum alloy before FSW. The FSW joints microstructure and fracture morphology of the original and HSNC specimens were researched by OM, SEM and TEM. The results showed that nanostructure layer zone (NLZ) was formed when GNS with shape similar to the "S" line was distributed in the thermal-mechanical affected zone (TMAZ) and the nugget zone (NZ) of the HSNC specimen. The lowest micro-hardness and fracture position of the original specimen occurred on the TMAZ of advancing side (AS). The lowest micro-hardness and fracture position of the HSNC specimen occurred on the NZ. The tensile strength of HSNC specimen was 6.4% higher than the original sample. The elongation of HSNC specimen was 14.1% more than the original specimen. The fracture mode of both specimens was toughness fracture. The fracture morphology of the HSNC was isometric dimple when the fracture morphology of original specimen were non-isometric dimple and avulsion dimple. Analysis showed that the NLZ of the FSW joints was beneficial to improving the strength and the plastic deformation capability simultaneously.
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