Solidification characteristics of aluminium alloys

这个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的部分液体演化和微观结构的形态。这项研究将集中在开发一种算法，预测新相开始结晶的温度，并计算它们的比生长速度。由于焊接过程中的冷却速度非常快，因此该算法必须考虑与液-固界面高速运动相关的现象。实验将在受控条件下进行，使用差示扫描量热仪(DSC)测量凝固过程中释放的热量。使用该仪器获得的冷却曲线将使用原始的数学处理进行分析，以便将理论和实验热速提取进行比较。这项工作将被用来研究焊缝中的热裂纹，这是由于残余应力超过未完全凝固的对接焊缝的强度而引起的。在焊接过程中进行热裂纹试验，以确定合金易发生裂纹的临界应力和临界温度。将在6xxx系列的两种合金中特别研究铁在熔合区中的作用。含铁的金属间化合物相在热裂纹的萌生过程中起着重要的作用。

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.