铝合金FSW拼焊板塑性变形规律研究

Plastic Deformation Behavior of Friction Stir Welded Tailor-Welded Blank of Aluminum Alloy

铝合金搅拌摩擦焊拼焊板焊缝各区力学性能的差异导致拼焊板成形时严重的不均匀性,降低了拼焊板的成形性能,极大地限制了铝合金拼焊板的应用。以2024铝合金搅拌摩擦焊拼焊板为研究对象,通过实验和有限元模拟系统研究接头力学性能失配对铝合金拼焊板塑性成形性能的影响规律和机理。对铝合金搅拌摩擦焊接头进行金相检验和硬度测试,根据接头组织及硬度分布特征,将搅拌摩擦焊接头划分为焊核区、热机影响区、热影响区以及母材区4个部分,以此建立搅拌摩擦焊接头的有限元模型,并对接头变形过程中的约束与协调变形规律进行分析。接头变形时拉伸应力在屈服应力最小的区域最低,在屈服应力较大的区域相应升高,且在接头中存在失配比交界处都会发生突变。从形变能的角度分析,这主要是由于力学性能失配而导致变形不协调及相互约束,表现在接头拉伸性能上就是屈服强度及屈服位置、抗拉强度、延伸率随接头各区失配比组合的差异。

Because of the differences in the mechanical properties of the welded joint district, the deformation law and forming characteristics of aluminum alloy Tailor Welded Blanks（TWB） joint is quite different compared to traditional sheet metal forming. This kind of mechanical properties mismatch often leads to the lower forming property of aluminum alloy TWB than that of the base metal, which greatly restricts the popularization and application of aluminum alloy TWB in automobile manufacturing industry. Based on the 2024-O aluminum alloy TWB of Friction Stir Welding, the influence law and influence mechanism of mechanical properties mismatch on the formability of aluminum alloy TWB was studied through the tests combined with the finite element method. Microstructure and hardness test of aluminum alloy FSW joint were carried out. According to the distribution of the hardness of welded joint, the FSW joint can be divided into Thermal Mechanical Affect Zone（TMAZ）, Heat Affect Zone（HAZ） and Base Metal（BM）. Finite element simulation of uniaxial tensile test was carried out based on the finite element model of FSW joint. Using the finite element model, the influence of mechanical properties mismatch of WNZ, TMAZ, and HAZ on tensile property of joint was studied. The results show that the stress is the lowest in minimum yield stress area, and correspondingly increases in larger yield stress area. The stress will mutate if there is mismatch ratio difference. In the views of the strain energy, the results are attributed to the nonuniform property of deformation and the constraint in the FSW joint, furthermore which leads to the variation of yield strength, location of yield, ultimate tensile strength and elongation with the diversity of mechanical properties mismatch.