Dispersoid-strengthened aluminum alloys for high temperature applications by microalloying transition elements of Zr, V, Cr, Mo and Sc

近年来，由于汽车和航空航天工业对高强度、低成本和轻质部件的需求，对高温(250-350摄氏度)铝合金的需求大幅增加。设计亚微米级和纳米级的铝基分散体是提高铝基复合材料高温强度和抗蠕变性能的有效途径。从我们在UQAC的初步工作中可以看到，一些过渡元素在凝固和热处理过程中可以形成二元弥散体(Al3M型)，或者在Mn、Si和Fe合金元素的存在下形成更复杂的三元或四元弥散体，这些元素在300oC以上的温度下通常是热力学和动力学稳定的。其中，微合金化过渡元素Zr、V、Cr、Mo和Sc的单独和组合添加因其高弹性模量、高熔点、低扩散系数和相对较低的成本而特别吸引人。为开发高温稳定、高强度弥散强化铝合金，拟选用变形铝制品用变形合金(3xxx系列)和铸件用铸造合金(Al-Si-Mg型)两种模型合金。首先使用Thermo-Calc软件进行热力学计算，以预测凝固和热处理过程中的相形成和组织。用热分析(TA)、差示扫描量热仪(DSC)、光学显微镜、扫描电子显微镜和透射电子显微镜(SEM和TEM)分析了两种合金在铸态和添加微合金化元素的热处理条件下的组织。在250-350℃的温度范围内，分别用力学性能和蠕变抗力来表征单独和复合添加Zr、V、Cr、Mo和Sc的弥散强化效果。弥散强化合金的长期热稳定性将在300℃下1000-2000小时的退火后进行评估。

The demand for aluminum alloys working at high temperatures (250 - 350 oC) has been greatly increased in recent years, driven by the automotive and aerospace industries requiring high strength, low cost and light components. The design of sub-micro and nano scale dispersoids in aluminum matrix is a powerful avenue to improve the strength and creep resistance at high temperatures. From our preliminary work at UQAC, it is seen that some transition elements can form either binary dispersoids (Al3M-type) during solidification and heat treatment or form more complex ternary or quaternary dispersoids in the presence of Mn, Si and Fe alloying elements, which often are thermodynamically and kinetically stable at temperatures well in excess of 300 oC. Among others, the individual and combined additions of microalloying transition elements of Zr, V, Cr, Mo and Sc are especially attractive due to high elastic modulus, high melting points, low diffusivity and relatively low cost. It is intended to select two model alloys - a wrought alloy (in 3xxx series) for deformed aluminum products and a foundry alloy (Al-Si-Mg-type) for castings - for developing dispersoid-strengthened aluminum alloys with high-temperature stability and high strength. The thermodynamic computation using the Thermo-Calc software will be first conducted to predict the phase formation and microstructure during solidification and heat treatment. The microstructures of two alloys at as-cast and heat-treated conditions with microalloying elements will be analyzed using thermal Analysis (TA), differential scanning calorimetry (DSC), optical microscopy, scanning electron and transmission electron microscopes (SEM and TEM). The dispersoid strengthening effect by individual and combined additions of Zr, V, Cr, Mo and Sc will be characterized in term of mechanical properties and creep resistance at the temperature range of 250 - 350 oC. The long term thermal stability of dispersoid-strengthened alloys will be evaluated after 1000 - 2000 h annealing at 300 oC.