焊前混合表面納米化對2A14鋁合金攪拌摩擦焊接頭微觀組織和力學(xué)性能的影響

焊前混合表面納米化對2A14鋁合金攪拌摩擦焊接頭微觀組織和力學(xué)性能的影響EFFECT OF HYBRID SURFACE NANOCRYSTALLIZATION COMBINATION BEFORE WELDING ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF FRICTION STIR WELDED 2A14 ALUMINUM ALLOY JOINTS

采用超音速微粒轟擊(SFPB)和表面機械滾壓處理(SMRT)相結(jié)合的混合表面納米化（HSNC）方法在2A14鋁合金表面制備出梯度納米結(jié)構(gòu)（GNS）表層，之后進行了攪拌摩擦焊（FSW）。利用OM、SEM和TEM對比研究了HSNC樣品和原始樣品FSW焊縫的微觀組織和斷裂形貌。結(jié)果表明，GNS表層類似“S”線復(fù)雜形式分布在HSNC樣品的熱機影響區(qū)（TMAZ）和焊核區(qū)（NZ）中形成了納米層區(qū)（NLZ），原始樣品顯微硬度最低處和斷裂位置均發(fā)生在前進側(cè)的TMAZ，HSNC樣品顯微硬度最低處和斷裂位置均發(fā)生在NZ；HSNC樣品的抗拉強度比原始樣品提高了8.8%，延伸率比原始樣品提高了14.1%，兩者的斷裂方式均為韌性斷裂，但原始樣品斷口形貌為非等軸韌窩和撕裂韌窩，HSNC樣品斷口形貌為等軸韌窩。分析表明， 由于納米晶的優(yōu)異性能，NLZ在提高焊縫強度的同時提高了塑性變形能力。

2A14 aluminum alloy is the important raw materials of aerospace, which belongs to the heat treatment aluminum alloy. As we all know, 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 specimen were researched by using optical microscope(OM), scanning electron microscopy (SEM) and transmission electron microscopy (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 were occurred on the TMAZ of advancing side(AS). The lowest micro-hardness and fracture position of the HSNC specimen were occurred on the NZ. The tensile strength of HSNC specimen was 8.8% higher than the original sample. The elongation of HSNC specimen was 14.1% more than the original specimen. The fracture mode of both specimens were toughness fracture. The fracture morphology of the HSNC was isometric dimple when which of the original specimen were non-isometric dimple and avulsion dimple. Analysis showed that the NLZ of the FSW joints was beneficial to improve the strength and the plastic deformation capability simultaneously.

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