【作者】 王文英；

【导师】 王玉；

【作者基本信息】 西北工业大学 ， 机械制造及其自动化， 2006， 硕士

【摘要】 本文主要研究了低碳钢Q235A和钛合金TC4搅拌摩擦焊接工艺以及不同工艺参数对焊接接头微观组织的影响。通过改变焊接过程中所施加的压力、搅拌头转速和焊接速度等工艺参数,来改善接头的微观组织,从而获得良好的接头性能。研究结果表明,搅拌头形状尺寸、工作压力、焊接速度和搅拌头转速这些焊接工艺参数对焊接质量有重要影响,从而初步研究钛合金的搅拌摩擦焊接。低碳钢可以采用搅拌摩擦焊技术焊接,接头的微观组织发生很大转变,晶粒细化十分明显,可以获得具有良好性能的焊接接头。在获得较好的焊接接头的前提下,在一定范围内改变焊接工艺参数对接头的组织影响不大,而在相同的焊接工艺参数下,采用辅助热源可使晶粒显著粗大。钛合金搅拌摩擦焊接头的组织焊接后发生明显细化,搅拌区金属在热和剧烈变形的作用下发生动态再结晶,冷却后组织为初生β相及转变β相;热机影响区在低于β相变温度下,因热和变形的作用,原粗大的α晶粒经动态再结晶形成细小的等轴α晶粒;接头的性能得到显著改善。 本文的另一个重要方面是采用与搅拌头共同运动的动态坐标系,建立并简化搅拌摩擦焊热输入数学模型,将瞬态温度场转化为准稳态温度场,来模拟搅拌摩擦焊过程的温度场。焊接热源主要来自于旋转的搅拌头与工件的摩擦以及搅拌针近旁金属的塑性变形,其中搅拌头与工件的摩擦是主要的,它包括搅拌头轴肩与工件表面的摩擦和搅拌针与工件的摩擦。在建立搅拌摩擦焊的热输入模型时,忽略焊接过程中金属塑性变形产生的热量,同时假设无热损失。将模拟结果与试验结果分析、对比和验证,研究焊接工艺参数与温度场分布的关系。 通过对模拟结果的分析,发现如果压力在焊接过程中保持不变,则焊接线能量仅取决于转速与焊速之比,当转速较大或焊速较小时,w/v则较大,单位长度焊缝上的热输入量高,模拟温度场的最高温度T_max值越大,热源横截面上的温度场与试验结果得到的微观组织分布相一致。更多还原

【Abstract】 In this paper, the objective of works was to design experimentation of welding mild steel Q235A and Ti—6A1—4V alloy by friction stir welds. In experimentation, we can get well mechanical capabilities and micro-structure of the tin-in by change force, rotate speed and jointing velocity. Then, to analyze the samples with the aim of describing the relation among the joining process, the resultant microstructures and ultimately the properties of the welds to demonstrate the feasibility of friction stir welding (FSW) for joining of high-melting point alloy. Microstructures of the defect — free welds of Ti-6Al-4V showed that, the welds region displayed several microstructurally distinct regions. The stir zone (SZ), because of dynamic recrystallization caused by intense deformation and high temperature exceeded β-transus during FSW, exhibited prior β grain and transformed β. The themo-mechanically-affected zone (TMAZ) was constituted of equiaxed a grain by the DRX. For mild steel Q235A, grains of SZ and HAZ were finer than those of base metal. The properties of the welds was improved extremely. If change the technics parameters in a limited range, the effect of the microstructures of the welds is not remarkable.Another important aspect of the work is simulating the temperature range of FSW by using finite element software ANSYS. Adopted a dynamic coordinate system moving with the stir pin to predigest the mathematics model, we transfer the transient-state to pre-steady state. The heat input includes which from friction between the tool and workpiece, and that derived from the deformation of the plastic metal. When setting up the heat transfer model, the heat from deformation of the plastic metal is ignored.To analyze, contrast and validate the results of simulation, it is found that jointing energy lies on the ratio between rotation and velocity. When the ratio is greater, the jointing energy is increased, and the peak temperature is greater. The temperature range of the cross section is consistent with the microstructures of the welds distribution.更多还原