Microstructure development and defect formation during welding of aluminum alloys

由于在降低制造成本的同时提高工艺精度的潜力，焊接工艺（例如电弧焊和激光束焊接）越来越多地用于在汽车和航空航天工业中接合铝合金。虽然使用这些工艺可以改善材料性能沿着直接减轻重量，但也必须考虑某些固有特性，如凝固开裂、微孔和热影响区降解。这些缺陷的存在，即使是少量的，通常也会导致焊接零件的拒收。 提出的研究的目的是通过减少缺陷的形成和改善焊接材料的性能来提高铝合金应用的焊接工艺的质量和生产率。这一目标将通过发现与焊接凝固动力学、合金成分和微观结构/缺陷成核和生长有关的新的基础知识来实现。将进行固化实验和半固态拉伸试验，以表征焊接过程中材料的行为。为了预测微观结构和缺陷的形成，沿着熔合区和热影响区的温度和应力/应变的演变，将开发中尺度和宏观尺度的计算机模拟。实验和中尺度模拟的结果将纳入宏观尺度模型，以便将不同长度尺度的现象联系起来。这种实验和多尺度建模的结合将能够评估焊接参数、合金成分和微观结构变化对缺陷形成的综合影响，以优化焊接工艺。这种优化对于开发铝合金在客运和公共交通车辆中的新的创新用途至关重要。

Welding processes, such as arc-welding and laser beam welding are increasingly being used to join aluminum alloys in the automotive and aerospace industries due to the potential of increasing process accuracy while reducing manufacturing costs. Although the use of these processes can result in improved material properties along with direct weight savings, certain inherent characteristics such as solidification cracking, microporosity, and heat-affected zone degradation must also be considered. The presence of these defects, even in small quantities, generally results in rejection of the welded part. The objective of the proposed research is to improve the quality and productivity of welding processes for aluminum alloy applications by reducing defect formation and improving the as-welded material properties. This objective will be realized through discovery of new fundamental knowledge relating welding solidification kinetics, alloy composition, and microstructure / defect nucleation and growth. Solidification experiments and semi-solid tensile tests will be performed to characterize the material's behaviour during welding. Computer simulations at the meso- and macro- scales will be developed in order to predict microstructure and defect formation along with the evolution in temperature and stress/strain in the fusion and heat-affected-zones. The results of the experiments and meso-scale simulations will be incorporated into the macro-scale model in order to link phenomena from different length-scales. This combination of experimentation and multi-scale modelling will enable assessment of the combined effects of welding parameters, alloy composition and microstructure variations on defect formation in order to optimize welding processes. Such optimization is critical for developing new innovative uses of aluminum alloys in passenger and mass transit vehicles.