铝合金FSW的搭接接头性能及搅拌头优化

发布时间：2018-07-26 09:09

【摘要】：搭接接头是搅拌摩擦焊(FSW)中常见的接头形式,在交通运输业应用广泛。为了改善搭接接头性能,本文从优化搅拌头形貌的角度出发,设计并制作了八种搅拌头,可分成两类:变螺纹搅拌头、变针长搅拌头。本文以2024-T4铝合金为研究对象,对搅拌头形貌影响FSW搭接接头的横截面形貌与拉剪性能的规律进行详细讨论。基于变螺纹搅拌头的试验结果发现:全螺纹搅拌头(F-pin)将材料堆积至搅拌针尖端;尖端半螺纹搅拌头(T-pin)除了将材料堆积至搅拌针尖端外,螺纹的起始端对周围材料有向下的作用力;根部半螺纹搅拌头(B-pin)在螺纹的末端及搅拌针尖端堆积材料;正反螺纹搅拌头(R-pin)的材料堆积区主要位于焊核区中部。拉剪试验结果表明:当前进侧受力时,在不同转速下T-pin均可获得最高的断裂载荷值;当后退侧受力时,T-pin所得接头的断裂载荷值均比B-pin与R-pin高。基于变针长搅拌头的试验结果表明:当针长为3mm时,前进侧的hook缺陷几乎呈水平分布,而后退侧包铝层向焊核中心延伸较多;当针长增加至4mm时,形成了明显向上弯曲的hook缺陷与cold lap缺陷;当针长为5mm时,hook缺陷和cold lap缺陷的高度有所减少,且cold lap缺陷向焊核区延伸的距离减小。拉剪试验结果表明:相同转速下针长由3mm增加至5mm后,断裂载荷先减小后增加;当针长为3mm时,接头断裂载荷值最高,前进侧与后退侧受力模式分别达到20825N与25665N。为了消除hook缺陷,本文采用了针长为2mm的搅拌头,以不扎透上板的方式成功地实现了搭接接头的有效连接,其断裂载荷为12185N。
[Abstract]:Lap joint is a common joint form in friction stir welding (FSW), and is widely used in transportation industry. In order to improve the performance of the lap joint, eight kinds of mixing heads are designed and manufactured from the point of view of optimizing the shape of the mixing heads. They can be divided into two types: variable thread mixing head and variable needle length mixing head. In this paper, taking 2024-T4 aluminum alloy as an object of study, the effects of mixing head morphology on cross section morphology and tensile shear properties of FSW lap joints are discussed in detail. Based on the experimental results of the variable thread mixing head, it is found that the full thread mixing head (F-pin) accumulates the material to the tip of the mixing needle, and the tip half thread stirring head (T-pin) accumulates the material to the tip of the needle. The starting end of the thread has downward force on the surrounding material, the root half threaded stirring head (B-pin) accumulates at the end of the thread and the tip of the stirring needle, and the material accumulation area of the positive and inverse thread stirring head (R-pin) is mainly located in the middle of the nuke zone. The results of tensile and shear tests show that T-pin can obtain the highest fracture load value at different rotational speeds and the fracture load value of T-pin joint is higher than that of B-pin and R-pin when the back side is loaded. The experimental results based on the variable-pin length mixing head show that when the needle length is 3mm, the hook defects on the forward side are almost horizontally distributed, while the aluminum coating on the receding side extends more to the core of the weld, and when the pin length is increased to 4mm, The hook defects and cold lap defects with obvious upward bending are formed, and the height of hooks and cold lap defects decreases when the pin length is 5mm, and the distance from cold lap defects to the nugget zone decreases. The results of tensile shear test show that when the pin length increases from 3mm to 5mm at the same rotational speed, the fracture load decreases first and then increases, and when the pin length is 3mm, the fracture load of the joint is the highest, and the stress modes of the forward and backward sides reach 20825N and 25665N, respectively. In order to eliminate the defect of hook, a mixing head with the length of 2mm is adopted in this paper, and the effective connection of the lap joint is successfully realized in the way of not penetrating the upper plate. The fracture load of the lap joint is 12185N.
【学位授予单位】：沈阳航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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