2024-O铝合金FSW拼焊板成形性能研究

Study on formability of 2024-O aluminum alloy FSW tailor-welded blanks

利用杯突试验方法测试了2 mm厚2024-O铝合金母材及搅拌摩擦焊拼焊板焊态和焊后退火态的杯突值,并利用ABAQUS数值模拟方法研究了杯突过程中试样应力和应变的分布特征,结合焊接接头的显微硬度测试和微观组织观察结果,讨论了影响拼焊板成形性能的主要原因。杯突试验结果表明,母材、焊态和焊后退火态拼焊板杯突值分别为11.53 mm、8.23 mm和10.49 mm。杯突试验过程的数值模拟结果表明,等效塑性应变最大位置是杯突试样的薄弱区,该区减薄率最大,是裂纹的起裂位置,这与杯突试验中裂纹出现的位置一致。在搅拌摩擦焊接过程中的热-机械作用下,焊核区Al基体发生动态再结晶导致的细晶强化以及Al_(2)CuMg相发生溶解产生的固溶强化是焊态接头焊核区显微硬度升高的主要原因。焊后退火处理过程中,焊核区Al基体晶粒尺寸增加以及从过饱和Al基体中脱溶析出的Al_(2)CuMg相发生粗化,导致退火态接头焊核区显微硬度明显下降。降低焊核区与周围金属的力学性能差异能够有效提高焊缝与周围金属的协同变形能力,进而提高拼焊板的成形性能。

Tailor-welded blanks(TWBs)were obtained by the friction stir welding(FSW)of 2 mm-thick 2024-O aluminum alloy.Cupping test method was utilized to assess the formability of base metal and the as-welded and as.annealed TWBs.In addition,the distribution characteristics of the stress and strain of the samples during the cupping process were simulated by the ABAQUS numerical simulation method.The main reason that affects the formability of the TWBs was analyzed based on the simulation results as well as microstructure observation and microhardness test results.The cupping test results show that the cupping values of base metal,as-welded and as-annealed TWBs are 11.53 mm,8.23 mm and 10.49 mm Respectively.The numerical simulation results of the cupping test show that the location of maximum equivalent plastic strain is the weak area of the cupping sample,which has the largest thinning ratio and is the crack initiation location,and it is consistent with the crack location in the cupping test.Under the thermo-mechanical action during the FSW process,the fine-grain strengthening caused by the dynamic recrystallization of the Al matrix in the weld nugget zone(WNZ)and the solid solution strengthening caused by the dissolution of the Al_(2)CuMg phase are the main reasons for the increase in the hardness of the WNZ of welded joint.The increase in grain size of the Al matrix and the coarsening of Al_(2)CuMg phase precipitated from the supersaturated Al matrix result in significant decrease in the microhardness of the WNZ after annealing.Reducing the difference of mechanical properties between the WNZ and the surrounding metal can effectively improve the coordinate deformation ability of the weld joint and the surrounding metal,thus improving the formability of TWBs.