Al-0.2Sc-0.04（Zr,Yb）合金高温蠕变机理

Based on the previous work, the high temperature creep of Al-0.2Sc-0.04（Zr，Yb） alloys (Yb: 0.01, 0.02, 0.03, and 0.04 wt%) is to be investigated. The mechanical properties (hardness and tensile strength) of alloys at the ambient temperature are optimized for different treatments (ageing, cold rolling+ageing, and pre-ageing+cold rolling+re-ageing). By high temperature creep tests, the minimum creep rate as the function of the applied stress and temperature can be obtained; furthermore, the influence of Yb concentrations and treatment methods on the creep behavior of alloys can also be studied.With the help of microstructure observations, the formation and evolution of Al3(Sc, Zr, Yb) precipitates can be characterized. The origin of grain refinement and substructure formation can be analyzed. With the measurement of the electrical resistance of alloys, the relationship between the electrical conductivity and Yb concentration and treatment methods can be obtained. At the same time, the evolution of microstructures during different treatments can be indirectly studied with the help of electrical conductivity measurements of alloys.Through these work, one can find that whether the threshold stress exists or not during the high temperature creep of Al-Sc-(Zr, Yb) alloys with the nano-sized coherence Al3(Sc, Zr, Yb) precipitate strengthening, or the microstructure condition and mechamism for the appearance of threshold stresses. The improved mechanism of high temperature creep of Al-Sc-(Zr, Yb) alloys will be proposed. The effects of Yb concentration on the heat resistance of alloys can be analyzed and studied. All these work will provide a theoretical and experimental support for the investigation and development of the new Al-Sc-(Zr, Yb) electrical conducting materials with super heat resistance.

在前期工作基础上，研究Al-0.2Sc-0.04(Zr, Yb)（Yb含量分别为0.01，0.02，0.03和0.04 wt.%）合金的高温蠕变。借助室温硬度和拉伸性能测试，确定合金在不同处理制度（时效，冷轧+时效和预时效+冷轧+再时效）下的优化条件。通过蠕变测试，建立最小蠕变速率与应力和温度关系，察知Yb含量和处理制度对蠕变行为的影响。借助微结构观察，获得Al3(Sc, Zr, Yb)沉淀形成和演化的一般规律。分析晶粒细化、亚结构形成的内在机理。通过电阻率测试，获得合金导电性与Yb含量和处理制度间关系，间接察知微结构演化的内在规律。通过这些工作，确定纳米Al3(Sc, Zr, Yb)共格沉淀强化的Al-Sc-(Zr, Yb)合金蠕变是否存在门槛应力，或找出门槛应力出现的微观条件或机理，提出改进的蠕变机制。分析Yb含量对合金耐热性能的影响，为新型超耐热导电铝合金的研发提供理论和实验支持。

微合金化Al-Sc-X（X=Zr，Ti，Yb和Gd等）合金具有优异的抗高温蠕变能力，有望替换汽车、航空器中需在中高温（200-400oC）工作的铸铁或Ti合金构件。本课题组率先注意到Al-Sc-X在超耐热导线领域的价值，发现冷轧和时效联合处理能显著提高合金力学性能和导电性，并申请了专利保护。但高温蠕变激活能明显偏小，蠕变机制仍需澄清。本项目在研究Al-0.24(Sc, Zr, Yb)合金蠕变机制的同时，通过Yb（部分）替换Zr或Sc，进一步优化其性能，主要结果如下：.（1）Al-0.2Sc-0.04(Zr, Yb)合金性能：在均匀化态，0.02%Yb部分置换Zr可使峰时效温度向高温移动约20oC，提高抗拉强度20MPa，提高导电性1.5%IACS。合金抗拉强度在峰时效+冷轧+峰时效态最高（206.0~224.4MPa），热挤+冷轧+峰时效态次之，而冷轧+峰时效态最低。Yb含量对导电性影响相对较小，20oC相对电导率为60.8~62.7%IACS。.（2）Al-0.2Sc-0.04(Zr, Yb)合金蠕变：冷轧或峰时效+冷轧预处理均能明显提高合金的抗高温蠕变能力。高温形变机制与应变速率有关：在低应变速率区是“存在门槛应力的位错蠕变”，而在高应变速率区或存在稳定亚结构时应是“存在门槛应力的恒定亚结构位错形变”。Yb部分替换Zr能适当提高合金的室温和高温力学性能，以及高温蠕变激活能。.（3）Al-0.2(Sc, Yb)-0.04Zr合金性能研究：为降低合金成本，对Yb部分替代Sc的Al-0.2(Sc, Yb)-0.04Zr合金性能进行了研究，发现随Yb含量增加，合金强度连续降低，导电性则不断改善。基于性价比考虑：Al-0.1Sc-0.1Yb-0.04Zr合金是一种不错的选择。.（4）Al-0.2Sc-0.02Zr-0.02Yb合金性能与冷轧量（半）定量关系：在相同冷热加工条件下，合金力学性能随冷轧量增加连续增加，但在面积减缩率为50%附近，增加规律发生了一定程度改变。相应微结构观察表明：当冷轧量低于50%时，时效过程中无明显亚结构形成，而当冷轧量高于50%时，时效将导致细小亚结构形成。该工作仍在进行中。.该研究进一步澄清了Al-Sc-X合金的蠕变机制，也为其在耐热导线、结构铝合金领域的应用提供了系统的参考数据。