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要求，对高温（250 - 350℃）铝合金的需求大大增加。在铝基体中设计亚微纳米分散体是提高铝基体高温强度和抗蠕变性能的有力途径。从我们在UQAC的初步工作中可以看出，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合金元素存在下形成更复杂的三元或四元弥散体，这些弥散体在超过300℃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有吸引力。本项目拟选择两种型号合金——用于变形铝制品的变形合金（3xxx系列）和用于铸件的铸造合金（al - si - mg型）——用于开发具有高温稳定性和高强度的分散体增强铝合金。首先使用hot - 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微观结构。采用热分析（TA）、差示扫描量热法（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热处理条件下的显微组织。在250 ~ 350℃的温度范围内，分别添加Zr、V、Cr、Mo和Sc对合金的分散强化效果和复合强化效果进行了力学性能和抗蠕变性能表征。在300℃下1000 ~ 2000 h退火后，对分散体强化合金的长期热稳定性进行评价。

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.