Tensile behavior of diffusion bonded AA6061 - AA6061 with variation in cooling method

Hot isostatically pressed AA6061 cladding is an important structural component of the high performance, Zr-laminated U-10Mo monolithic fuel system for the application in research and test reactors. In this study, the mechanical behavior of two diffusion bonded aluminum alloy, AA6061, was examined using tensile testing. Solid-to-solid diffusion bonding between two pieces of AA6061 was performed by isothermal annealing at 560 °C for 1.5 h, and diffusion couples were subsequently cooled via three different cooling methods: furnace cooling, air cooling, and water quenching. Dog-bone shaped tensile specimens, with 10 mm in gauge length (with diffusion bonded interface in the middle), and 1.5 × 1.5 mm2 gauge cross-sections, were fabricated from the diffusion bonded AA6061 by electro-discharge machining. Yield strength (% EL at failure) of furnace cooled, air cooled and water quenched tensile specimens determined was 82–89 MPa (10–30%), 112–116 MPa (10–14%), and 149–164 MPa (10–17%), respectively. This variation in mechanical behavior was examined with cooling-rate dependent, concentrated precipitation of Mg2Si at the diffusion bonded interface, with due respect for mechanical properties of the AA6061 alloy that inherently vary as a function of cooling rate from 560 °C. Finite element analysis using ABAQUS was employed to augment experimental findings with the appropriate microstructural constituents and alloy properties. Results suggest that the strength is dominated by matrix/bulk properties of AA6061, while ductility is strongly influenced by the cooling method dependent presence of Mg2Si precipitates at the interface.

热等静压AA6061包壳是用于研究和试验反应堆的高性能、锆层压U - 10Mo整体燃料系统的重要结构部件。在本研究中，使用拉伸试验检测了两种扩散结合的铝合金AA6061的力学性能。两片AA6061之间的固 - 固扩散结合是通过在560°C下等温退火1.5小时进行的，随后扩散偶通过三种不同的冷却方法冷却：炉冷、空冷和水淬。通过放电加工从扩散结合的AA6061制备出狗骨形拉伸试样，其标距长度为10毫米（扩散结合界面在中间），标距横截面为1.5×1.5平方毫米。炉冷、空冷和水淬拉伸试样测定的屈服强度（断裂时的延伸率%）分别为82 - 89兆帕（10 - 30%）、112 - 116兆帕（10 - 14%）和149 - 164兆帕（10 - 17%）。这种力学性能的变化通过扩散结合界面处依赖冷却速率的Mg₂Si集中沉淀进行了检测，同时充分考虑了AA6061合金的力学性能，其本身随从560°C冷却的速率而变化。使用ABAQUS进行有限元分析，以适当的微观结构成分和合金性能来补充实验结果。结果表明，强度主要由AA6061的基体/整体性能决定，而延展性则受到界面处依赖冷却方法的Mg₂Si沉淀的强烈影响。