2A97铝锂合金搅拌摩擦焊焊缝的微观组织特征

对厚度为25 mm的T851态2A97铝锂合金进行搅拌摩擦焊焊接,利用显微硬度、金相显微镜(OM)和透射电镜(TEM)等对焊缝的显微硬度和微观组织进行研究.结果表明:接头基材硬度最高,热影响区和热机影响区硬度降低,焊缝中心硬度又升高,硬度最低位置在热影响区.焊核区发生动态再结晶,形成细小等轴的晶粒;焊核区S′相全部溶解,T1相儿乎全部溶解,在随后的冷却和时效过程中,焊核区析出GP区和细小弥散的δ′相；热影响区的T1相部分溶解,S′相全部溶解,析出θ"相、δ′相和δ′/β′的复合相.

Microstructural characteristics of joint line of friction stir welding of 2A97 Al-Li alloy

2A97-T851 aluminium lithium alloy with thickness of 25 mm was welded by friction stir welding.Using microhardness test,optical microscopy,transmission electron microscopy,the microhardness distribution and microstructure evolution of the friction stir welded joint were investigated.The results indicate that,the base material presents the highest hardness which decreases within the heat affected zone and heat mechanical affected zone,while in the nugget zone the hardness increases to certain extent.The lowest hardness is found in the heat affected zone.The refined grains observed within the weld nugget attributed to the dynamic recrystallization because the weld nugget experiences both high temperature and stirring rotation deformation.In the nugget,the S′ precipitates and most of the T1 phase dissolve.During nature aging after cooling,the G.P.zone and fine δ′ phase re-pricipitate.In the heat affected zone,S′ phase and partial T1 dissolve.θ″,δ′ and δ′/β′ composites are found in this zone.