铝合金双轴肩搅拌摩擦焊搅拌头设计、接头组织和性能研究

发布时间：2018-01-24 09:26

本文关键词： 双轴肩搅拌摩擦焊搅拌头设计铝合金微观组织　出处：《南昌航空大学》2017年硕士论文　论文类型：学位论文

【摘要】：双轴肩搅拌摩擦焊技术(Bobbin Tool Friction Stir Welding,BTFSW)作为搅拌摩擦焊领域的拓展技术,利用下轴肩代替背部刚性垫板,大大减小了垂直方向上的锻压力,降低了装夹要求及夹具成本,同时消除了根部未焊透问题。因此在工程实践中有很高的应用价值。本文针对4mm厚6061-T6铝合金设计了不同的轴肩形貌及搅拌针形貌,并进行双轴肩搅拌摩擦焊试验,研究了搅拌头形貌和焊接工艺参数对接头成形及抗拉强度的影响。分析了双轴肩搅拌摩擦焊接头各区域组织特点,并总结接头中容易出现的缺陷类型及缺陷对接头抗拉强度的影响。主要的研究成果如下:在搅拌头为平面轴肩和圆柱形搅拌针不变的情况下,焊接接头随着上轴肩下压量的减小,接头上表面飞边量先减小后增加,下表面飞边量逐渐增加;随着旋转速度的增加,接头表面易出现鱼鳞纹且逐渐由不均匀变得均匀;随着焊接速度增加,焊接接头上表面后退侧飞边从无到有,且飞边量增加;同时上下表面接头鱼鳞纹逐渐变得均匀。根据双轴肩搅拌摩擦焊接头中微观组织特点,接头可分为母材区(BM)、热影响区(HAZ)、热力影响区(TAMZ)及焊核区(WNZ)四个区域,其中焊核区为等轴晶粒,热力影响区晶粒为发生塑性变形的板条状晶粒,热影响区为发生粗化的板条状晶粒。通过正交试验发现各因素对接头宏观形貌影响的主次顺序依次为:轴肩形貌、旋转速度、轴肩下压量、搅拌针形貌、焊接速度。各因素对接头抗拉强度影响的主次顺序依次为:轴肩下压量、轴肩形貌、搅拌针形貌、旋转速度、焊接速度。焊接头容易出现的缺陷类型分别为孔洞缺陷、弱结合缺陷、S线缺陷;其中孔洞缺陷易出现在前进侧WNZ与TMAZ交界处和WNZ偏向后退侧区域,弱结合缺陷易出现在前进侧WNZ与TMAZ交界处,S线缺陷易出现在WNZ偏向后退侧区域。通过对比发现接头中S线缺陷区域的冶金结合程度不同,如果该区域冶金结合程度较差,则可能会影响接头的抗拉强度,如果该区域的冶金结合程度较好,则对接头的抗拉强度没有影响。另外S线缺陷的形状也会影响接头的抗拉强度。正交试验优化结果表明:当搅拌头形貌为内凹带螺旋凹槽轴肩形貌和三平面带右螺纹搅拌针形貌,工艺参数为上轴肩下压量0.05mm,下轴肩下压量0.15mm,焊接速度120mm·min-1,旋转速度520r·min-1时焊接接头抗拉强度最高,接头抗拉强度为230.36 MPa。
[Abstract]:The technology of bobbin Tool Friction Stir welding BTFSWs is used to expand the field of friction stir welding. The lower shaft shoulder is used to replace the back rigid pad, which greatly reduces the forging pressure in the vertical direction, the clamping requirement and the fixture cost. At the same time, the problem of root penetration is eliminated, so it has high application value in engineering practice. In this paper, different shaft-shoulder morphology and stirring needle morphology are designed for 6061-T6 aluminum alloy with 4mm thickness. The effects of joint morphology and welding parameters on the joint forming and tensile strength were studied. The microstructure characteristics of the joint were analyzed. The main research results are as follows: under the condition that the mixing head is flat shaft shoulder and cylindrical stirring needle is unchanged. With the decrease of shoulder pressure, the upper surface flange decreases first and then increases, and the lower surface flange increases gradually. With the increase of rotation speed, the surface of the joint is easy to appear scales and gradually change from uneven to uniform. With the increase of welding speed, the flange of the receding side of the upper surface of the welded joint starts from nothing to existence, and the amount of flying edge increases. At the same time, the upper and lower surface joints gradually become uniform. According to the microstructure characteristics of friction stir welding joints, the joints can be divided into base metal area (BMN), heat affected zone (HAZ). Tam Z) and WNZ are four regions, in which the nugget zone is equiaxed grain, and the thermal effect zone grain is the strip grain of plastic deformation. The main and secondary order of the influence of various factors on the macroscopic morphology of the joint is as follows: axial shoulder morphology, rotation speed, axial shoulder pressure, stirring needle morphology. Welding speed. The main and secondary order of the influence of each factor on the tensile strength of the joint is as follows: the axial shoulder pressure, the shaft-shoulder morphology, the stirring needle morphology, the rotation speed. Welding speed. The defect types of welding joint are hole defect, weak joint defect and S-line defect respectively. The hole defects are easy to appear at the junction of WNZ and TMAZ on the forward side and on the backward side of the WNZ bias, and the weak binding defects at the junction of WNZ and TMAZ on the forward side. S-line defects are prone to occur in the receding region of WNZ bias. It is found that the metallurgical bonding degree of S-line defect region in the joint is different, if the metallurgical bonding degree is poor in this area. The tensile strength of the joint may be affected if the metallurgical bonding in the region is good. In addition, the shape of S-line defects will also affect the tensile strength of the joint. The orthogonal test results show that:. The shape of the mixing head is the shape of the shaft shoulder of the inner concave spiral groove and the shape of the stirring needle with the right thread of the three-plane belt. The technological parameters are as follows: the pressure of the upper shoulder is 0.05mm, the pressure of the lower shoulder is 0.15mm, and the welding speed is 120mm 路min-1. The tensile strength of welded joints is the highest at 520r 路min-1 rotation speed, and the tensile strength of welded joints is 230.36 MPa.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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