【摘要】 7475铝合金具有出色的力学性能,被广泛应用于航空航天领域.使用回填式搅拌摩擦点焊进行焊接能够有效地消除传统搅拌摩擦点焊接头中的匙孔,使力学性能得到大幅提高.但是,对于如7000系高强铝合金进行回填式搅拌摩擦点焊实验时,依然存在力学性能不良、得不到良好焊点的问题,这是由于在对高强铝合金进行回填式搅拌摩擦点焊时,需要更大的热输入才能使母材受搅拌作用形成塑性材料.当焊接热输入较大时,焊点内易产生裂纹和孔洞等缺陷从而影响焊点的力学性能.本研究采用激光共聚焦显微镜、电子扫描显微镜(SEM)对链状孔洞的形貌特点进行了系统的分析,并对链状孔洞的产生原因进行了分析讨论,同时进行了一系列工艺参数实验研究工艺参数对焊点内链状孔洞的影响.研究结果表明,7475铝合金回填式FSSW焊点在较高热输入情况下搅拌区(SZ)内存在对称分布且呈现链状的孔洞,链状孔洞的方向与焊接过程中塑性材料的流动方向一致,这是由于焊接过程中焊具的搅拌以及焊接温度的不断提高,母材中原本存在的金属间化合物(IMC)被焊具打碎并随着材料流动方向汇聚在SZ内,当SZ内温度达到共晶温度时,IMC与Al发生了共晶反应造成了熔化.此外,随着搅拌套下压深度增加,链状孔洞密集程度上升;随着搅拌套运动速率增加,链状孔洞密集程度下降;随着焊具旋转速度的增加,链状孔洞密集程度上升.更多还原

【Abstract】 The 7475 aluminum alloy has excellent mechanical properties and is widely used in the aerospace industry.The use of refill friction stir spot welding(FSSW) for welding can effectively eliminate the keyhole in the traditional friction stir spot welding head,so that the mechanical properties are greatly improved. However,when the refill FSSW was performed on a 7000 series high-strength aluminum alloy,the mechanical properties were still poor,and a good solder joint was not obtained. When refill FSSW was applied to a high-strength aluminum alloy,more heat input was required to form plastic material from the stirring of the base material. When the welding heat input is high,cracks and holes were easily generated in the joint. Such defects affect the mechanical properties of the joint. In this study,the morphological characteristics of chain pores were analyzed by laser confocal microscopy and scanning electron microscopy(SEM),and the causes of chain holes analyzed. At the same time,a series of process parameter experiments were carried out to study the influence of process parameters on the chain holes in the solder joints. The results showed that the 7475 aluminum alloy refilled FSSW solder joints have symmetric distribution and chain holes in the SZ region with higher heat input. The direction of the chain hole was consistent with the flow direction of the plastic material during the welding process. The existing intermetallic compound(IMC) in the base metal was crushed by the welding tool and aggregated in the SZ along the flow direction of the material due to the stirring of the welding tool and continuous improvement of the welding temperature during the welding process. When the temperature in SZ reaches the eutectic temperature,IMC reacts with Al to cause melting. In addition,as the depression depth increases,the density of the chain holes increases. As the depressing velocity of the tools increase,the density of the chain holes decreased. As the rotation speed increases,the chain hole density increases.更多还原