异种热处理状态6061铝合金FSW接头组织性能及金属流动性可视化研究

发布时间：2018-04-26 01:18

本文选题：搅拌摩擦焊 + 6061铝合金　；参考：《江苏科技大学》2017年硕士论文

【摘要】：6061铝合金是6系铝合金当中应用最多的牌号之一,广泛应用于工业各领域。搅拌摩擦焊(FSW)作为一种“年轻”的固态焊接方法为焊接铝合金提供了一种优质、高效的新方法。但是,目前学术界对FSW焊缝金属的流动方式、接头成型机理等仍处在实验探索阶段,尚无权威定论,因此对其进行研究具有十分重大的意义。本论文对6061-T6和6061-O铝合金进行了多种对接方式的搅拌摩擦焊接。焊后对各接头形式的焊缝进行了组织和性能的分析,并通过标记材料示踪手段研究了异种热处理状态6061铝合金搅拌摩擦焊接头的金属流动性特征。标记材料示踪法是一种常用的研究材料流动的可视化研究方法,选择铜粉和铜箔作为标记材料能够直观而有效的观察接头塑性金属的迁移方式。拉伸实验结果表明,O-O接头与O-T6接头属于塑性断裂。T6-T6接头属于准解理断裂。T6-T6接头的显微硬度曲线呈W形,焊核区硬度约为母材区的70%;O-O接头硬度呈现抛物线形,焊核区硬度最高,约为母材区的125%;T6-O接头与O-T6接头的显微硬度曲线虽然总体近似于镜像对称关系,但在局部也存在明显的区别。接头组织方面,焊核区为细小的等轴晶,晶粒直径约3-5μm,第二相颗粒分布在晶粒内部,第二相主要成分为Mg2Si;热机影响区晶粒被拉长,呈长条状,轴肩影响区由于动态再结晶过程中热量散失迅速,晶粒最为细小。搅拌针螺纹提供了FSW接头塑性金属垂直方向流动的驱动力,搅拌针的螺纹带动焊核区上层金属向下方迁移,下层金属不会发生逆向迁移,只能向更下层迁移。上层金属无论在垂直还是水平方向上的流动性均更强,迁移距离更远。在水平方向上,螺纹搅拌针带动焊核区塑性金属旋转运动多个周期,而无螺纹搅拌针仅带动塑性金属发生半个旋转周期的迁移。焊核区金属的主要来源是前进侧母材,随着焊核区金属随搅拌针螺纹向下方迁移,后退侧塑性金属受到挤压绕过焊核区进入焊核区上方的空腔。前进侧金属首先进入焊核区,并发生剧烈的机械搅拌变形,后退侧金属进入焊核时间较晚,受到的机械作用相对较弱。轴肩影响区金属主要来源于后退侧,当后退侧金属为O态时轴肩影响区内的塑性金属流动更加剧烈,能够迁移到更远的距离,当后退侧金属为T6态时轴肩影响区内的塑性金属流动性较弱。此外,O态金属一侧的热机影响区宽度更大,T6态母材一侧的热机影响区宽度相对较窄。
[Abstract]:6061 aluminum alloy is one of the most widely used six-series aluminum alloys. It is widely used in various fields of industry. FSW (friction stir Welding), as a "young" solid state welding method, provides a high quality and high efficiency method for aluminum alloy welding. However, the current academic research on the flow mode of FSW weld metal and the forming mechanism of joint is still in the stage of experimental exploration, and there is no authoritative conclusion, so it is of great significance to study the flow mode of FSW weld metal and the mechanism of joint forming. In this paper, friction stir welding of 6061-T6 and 6061-O aluminum alloy is carried out. After welding, the microstructure and properties of the welded joints were analyzed, and the metal fluidity characteristics of friction stir welding joints of 6061 aluminum alloy with dissimilar heat treatment were studied by means of tracer materials. The tracer method is a common visual method to study the flow of materials. Selecting copper powder and copper foil as marking materials can directly and effectively observe the transfer mode of plastic metals in joints. The results of tensile test show that the microhardness curve of the joint between O-O and O-T6 belongs to plastic fracture. T6-T6 joint is quasi-cleavage fracture. The microhardness curve of T6-T6 joint is W shape, and the hardness of 70o joint is parabola, and the hardness of weld nugget zone is the highest. The microhardness curves of 125 T6-O joints and O-T6 joints in the base metal region are similar to mirror symmetry, but there are obvious differences between them. In connection with the microstructure of the joints, the nugget zone is a fine equiaxed crystal, the grain diameter is about 3-5 渭 m, the second phase is distributed inside the grain, the main composition of the second phase is mg _ 2Si, and the grains in the heat engine affected zone are elongated and long. Due to the rapid heat loss in the dynamic recrystallization, the grain size is the smallest in the shaft-shoulder affected zone. The stirring needle thread provides the driving force for the vertical flow of the plastic metal in the FSW joint. The thread of the stirring needle drives the upper layer metal to move downwards in the nuke zone, but the lower layer metal can only migrate to the lower layer instead of the reverse migration. The upper metal is more fluidity in vertical and horizontal direction, and the distance of migration is longer. In the horizontal direction, the screw stirring needle drives the rotation of plastic metal in the nuke zone for several periods, while the non-threaded needle only drives the transfer of the plastic metal for half a rotation cycle. The main source of the metal in the nugget zone is the forward base metal. As the metal in the nugget zone moves down with the stirring needle thread, the plastic metal in the receding side is bypassed into the cavity above the nugget zone by squeezing the nugget zone. The metal on the forward side first enters the nugget zone, and the mechanical stirring deformation occurs, and the metal in the receding side enters the nugget later, so the mechanical action is relatively weak. The metal in the shaft-shoulder affected zone mainly comes from the receding side. When the metal in the receding side is in O state, the plastic metal flow in the shaft-shoulder influence zone is more intense and can migrate to a longer distance. When the metal in the receding side is in the T 6 state, the fluidity of the plastic metal in the axial shoulder affected zone is weak. In addition, the width of the heat engine affected zone on the side of O state metal is larger than that on the side of the base metal of T 6 state, and the width of the heat engine influence zone on the side of T 6 state is relatively narrow.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.14

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