## 1 Introduction  
Lightweight materials and a reduction in their manufacturing costs have been topics pursued in the automotive, aerospace, marine, and other fields [1; 2; 3]. Lightweight materials replace steel and iron materials with light metals or non-metals without compromising the product's strength. These materials can be joined together by gluing [4] or riveting [5]. Still, when it comes to complex assembly situations such as the formation of multiple presses [6], these joining methods are challenging to meet their requirements, and the TWBs have successfully solved this problem. The TWBs are preformed parts made of two or more alloy plates welded together to achieve the comprehensive performance of joining between different plates (dissimilar alloys or different thicknesses). Then, cold or hot stamping techniques are used to form the final net-formed parts. With the increasing emphasis on automotive lightweight materials, the Al-Al TWBs have been well applied in the automotive field, and [PERSON] et al. [7] reported that the use of aluminum body materials could save 5-7% of the fuel and reduce the deadweight by about 10% compared with steel body materials. Unequal-thickness aluminum alloy [8] and dissimilar aluminum alloy [9] TWBs were studied, and it was found that the increase in the thickness ratio of the TWBs during stamping leads to the offset of the FZ. In contrast, the differences in alloy compositions and mechanical properties affect the failure location of the dissimilar TWBs. The 6000 series aluminum alloys are renowned for their high specific strength, exceptional specific stiffness, excellent corrosion resistance, and notable plasticity [10]. These qualities impart machinability to thin-sheet aluminum alloys, making them preferred for various automotive parts and components, including hoods, trunk lids, inner and outer door panels, and door-side frames [11]. However, the aluminum alloy TWBs' formability is constrained compared to the BM. This limitation primarily stems from the inherent disparities in the microstructure and the properties between the FZ and the BM [12], prompting further investigation into the post-veld heat treatment process. [PERSON] et al. [13] suggested that the formability of the AA6061 and the AA2014 TWBs, which have undergone solution heat treatment, surpasses that of untreated counterparts, surpassing that of the BM. [PERSON]'s research [14] indicated that adopting an appropriate preheating temperature for the AA2219 TWBs enhances formability while preserving FZ strength and preventing abnormal grain growth. Notably, the forming ability of the TWBs improved significantly when the preheating temperature was raised from 300 \({}^{\circ}\)C to 350 \({}^{\circ}\)C. [PERSON] et al. [15] employed a novel approach to enhance formability by conducting a simultaneous quenching and forming treatment for the aluminum alloy TWBs within the forming die. The introduction of controlled plastic deformation after welding has proven effective in bolstering the strength of welded joints. [PERSON] et al. [16] applied rolling to the weld excess metal of an aluminum alloy to ameliorate softening phenomena, subsequently developing a post-veld composite treatment process [17] encompassing solution heat treatment, artificial aging treatment, and cold rolling. This method achieved synergistic strengthening involving second-phase strengthening and dislocation strengthening. Nevertheless, it is crucial to note that this type of strengthening can lead to over-strengthening (resulting in joint hardness exceeding that of the BM) and uneven plastic deformation in different regions, potentially diminishing the forming capabilities of the TWBs. Previous studies that aimed at enhancing the formability of aluminum alloy TWBs have mainly focused on the forming process itself and a single pre-veld or post-veld heat treatment process [14; 18; 19; 20], with limited exploration of alternative post-treatment methods.