Solidification characteristics of aluminium alloys

该项目的主要目标是了解合金成分在焊缝缺陷形成中的作用，同时考虑到凝固过程中分数液体的演变和微观组织的形态。研究的重点是开发一种算法，预测新相开始结晶的温度，并计算它们的特定生长速率。由于焊接过程中的冷却速度非常快，该算法必须考虑到与液固界面高速移动有关的现象。实验将在受控条件下进行，使用差示扫描量热计（DSC），测量凝固过程中释放的热量。用该仪器得到的冷却曲线将使用原始的数学处理进行分析，以便可以比较理论和实验的热速率提取。这项工作将用于研究焊缝中的热裂，这是由残余应力超过未完全凝固的对接焊缝的强度引起的。进行焊接热裂实验，了解合金易发生裂纹的临界应力和临界温度。在6XXX系列的两种合金中，将特别研究铁在熔合区的作用。结果表明，含铁的金属间相对热裂的发生起着重要的作用。

The main goal of this project is to understand the role of alloy composition in the formation of defects in welds, taking into account the fraction liquid evolution and the morphology of the microstructure during solidification. The research will focus on the development of an algorithm predicting the temperature where new phases start to crystallize and calculating their specific growth rates. Since cooling rates are very fast in welding, the algorithm will have to take into account phenomena associated to liquid-solid interface moving at high velocities. Experimentations will be conducted in controlled conditions by using a differential scanning calorimeter (DSC), which measures the heat released during solidification. The cooling curves obtained with this instrument will be analysed using an original mathematical treatment so that it will be possible to compare theoretical and experimental heat rate extraction. This work will be used to investigate hot cracking in welds, which is caused by residual stresses exceeding the strength of the not completely solidified butt weld. Experimentations of hot cracking in welding will be conducted to know the critical stress and critical temperature where the alloy is prone to crack. The role of iron in the fusion zone will be particularly investigated in two alloys of the 6XXX series. It seems that intermetallic phases containing iron could play an important role in the initiation of hot cracking.