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液体的分数演化和微观结构的形态。该研究将集中在预测新相开始结晶的温度并计算其比生长速率的算法的开发上。由于焊接中的冷却速率非常快，因此该算法必须考虑与高速移动的液-固界面相关的现象。实验将在受控条件下进行，使用差示扫描量热计（DSC），测量固化过程中释放的热量。将使用原始数学处理方法分析用该仪器获得的冷却曲线，以便可以比较理论和实验热耗率提取。这项工作将被用来调查热裂纹的焊缝，这是造成的残余应力超过强度的不完全凝固对接焊缝。进行焊接热裂纹试验，以确定合金易产生裂纹的临界应力和临界温度。铁在熔合区中的作用将在6XXX系列的两种合金中进行特别研究。含铁的金属间化合物相在热裂纹萌生中起重要作用。

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.