Mechanism-based characterization of the texture influence on the corrosion and corrosion fatigue properties of zinc-based wrought magnesium alloys

本文旨在研究含稀土和含钙挤压Mg-Zn合金在空气和腐蚀介质中循环加载的损伤机理。先前的研究结果表明，与含al - Mg标准合金相比，含RE和ca的挤压镁合金在疲劳载荷和应力腐蚀开裂（SCC）条件下具有显著改善性能的潜力。通过添加合适的合金元素，设置合适的挤压参数，可以得到晶粒细、织构弱化同时进行的镁合金，即通过改变变形机制，可以同时获得成形性、提高疲劳强度、提高耐腐蚀性和减少亚临界裂纹扩展等性能。要减少孪晶的形成，不仅要通过弱织构和细晶粒，而且要通过均匀的晶粒分布和合适的析出物来减少孪晶的形成，同时又不妨碍滑移过程。通过一方面提高疲劳强度，另一方面提高耐蚀性，目的也是为了显著提高抗SCC性能。研究了不同的工艺参数和产生的微观结构对空气循环载荷和SCC条件下损伤机制的影响，并从研究结果中得出了一个基本的工艺-微观结构-性能关系。通过将应力-应变滞后过程与微观组织变化联系起来，表征了腐蚀介质循环加载下织构、各向异性和拉压不对称的复杂相互作用。对工艺-显微组织-性能关系的理解有助于开发一组新的高性能挤压镁合金，并将知识转移到镁合金的疲劳和腐蚀行为上，这为通过铸轧开发薄板合金奠定了基础。虽然该课题具有很高的科学和经济潜力，但目前还没有对其进行研究，也没有对织构对疲劳行为的影响，特别是对SCC的损伤机制进行研究。

The proposal aims to investigate the damage mechanisms of RE- and Ca-containing extruded Mg-Zn alloys under cyclic loading in air and corrosive media. The results of previous work allow the conclusion that RE- and Ca-containing extruded Mg alloys have the potential of significantly improved properties under fatigue loading and stress corrosion cracking (SCC) conditions compared to the Al-containing Mg standard alloys. By adding suitable alloying elements and setting suitable extrusion parameters, Mg alloys with fine grain sizes and simultaneous texture weakening are to be produced, i.e. by changing the deformation mechanism, properties such as formability, increased fatigue strength, increased corrosion resistance and reduced subcritical crack propagation are to be combined. The formation of twins shall be reduced, not only by weak textures and fine grain sizes but also by homogeneous grain size distributions and suitable precipitates which reduce the formation of twins and at the same time do not hinder the slipping processes. By increasing the fatigue strength on the one hand and the corrosion resistance, on the other hand, the aim is also to achieve a significant improvement of the resistance to SCC. The different processing parameters and the resulting microstructure are to be investigated for their influence on the damage mechanisms under cyclic loading in air and under SCC conditions, and a fundamental process-microstructure-property relationship is to be derived from the findings. By correlating the course of the stress-strain hystereses with the microstructural changes, the complex interaction of the texture, the resulting anisotropy, and the tension-compression asymmetry under cyclic loading in the corrosive medium is to be characterized. The understanding of the process-microstructure-property relationships allows the development of a new group of high-performance extruded Mg alloys and the knowledge transfer to the fatigue and corrosion behavior of Mg sheet alloys in general, which forms a basis for sheet alloy development through cast rolling. Although the topic has a high scientific and economic potential, it has not been investigated yet, nor have the present damage mechanisms been researched regarding the texture influence on fatigue behavior and in particular the SCC.