Prediction of the residual strength of corroded high-strength aluminum alloys under uniaxial loading by numerical simulations

高强度铝合金由于其高强度和良好的耐腐蚀性，被用于各种部件中。然而，如果钝化层被破坏，例如氯离子，则耐腐蚀性将失效。局部腐蚀现象（以下简称缺陷）和点蚀在损伤过程中发生。这导致材料的强度降低。迄今为止，基于点蚀状态的单轴拉伸载荷下的残余强度预测对于高强度铝合金来说还不是最先进的技术。本研究项目的目的是通过标准表面检测预测残余强度。对两种铝合金（EN AW-2xxx和EN AW-7xxx）进行了研究，将现有的钢材预测模型转移到高强度铝合金上。现有的模型将通过观察出现的缺陷的形态和分布来改进。在不同条件下进行了腐蚀试验，建立了模型。通过使用描述缺陷形状和分布的参数来量化每个样品的点蚀。利用微光学三维图案表面测量装置对缺陷进行非破坏性表征。随后对拉伸试验进行有限元模拟，得到缺陷形状、分布与残余强度之间的解析关系。这将通过回归分析来实现。此外，还进行了应力分析，以讨论关键缺陷的形状和分布。这将通过加权因子来实现。最后，通过分析关系和加权因子得到了剩余强度模型。通过将当前损坏状态的计算强度与未腐蚀材料的强度相关联，可以计算出独立的材料减少系数。因此，该模型可用于进一步的铝合金残余强度预测。

High-strength aluminum alloys are used in a variety of components due to their high strength and good corrosion resistance. However, the corrosion resistance will fail if the passive layer is damaged, e.g. by chloride ions. Local corrosion phenomena (henceforth referred to as defects) and pitting corrosion occur as the damage is proceeding. This leads to a strength reduction of the material. The residual strength prediction under an uniaxial tensile loading based on the state of pitting corrosion is, thus far, not state of the art for high-strength aluminum alloys. The aim of this research project is the prediction of residual strength by a standard surface inspection. Two aluminum alloys (EN AW-2xxx and EN AW-7xxx) are carried out to transfer existing prediction models for steels to the high-strength aluminum alloys. The existing models will be improved by observing the morphology and distribution of the occurring defects. Corrosion tests at different conditions are realized to develop the model. The gained pitting corrosion will be quantified for each sample by using parameters to describe the shape and the distribution of the defects. The characterization of the defects will be non-destructive using a micro-optical 3D pattern surface measuring device. Subsequent FE-simulations of tensile tests are executed to attain analytical relations between the defect shape, distribution and residual strength. This will be achieved by means of a regression analysis. Additionally, stress analyses are performed to discuss critical defect shapes and distributions. This will be implemented by weighting factors. Finally, the residual strength model is obtained by the analytical relations and the weighting factors. The independent material reduction factor will be calculated by relating the calculated strength of the current damage state to the strength of the non-corroded material. Thus, the model to predict the residual strength can be applied to further aluminum alloys.