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

高强度铝合金因其高强度和良好的耐腐蚀性而被广泛应用于各种部件。然而，如果钝化层被损坏，例如被氯离子破坏，耐腐蚀性将会失效。随着损伤的进行，会发生局部腐蚀现象(以下称为缺陷)和点蚀。这会导致材料的强度降低。到目前为止，基于点蚀状态的单轴拉伸载荷下的剩余强度预测对于高强度铝合金来说还不是最先进的。本研究项目的目的是通过标准表面检测来预测剩余强度。采用两种铝合金(EN AW-2xxx和EN AW-7xxx)将现有的钢的预测模型转化为高强铝合金。通过观察发生缺陷的形态和分布，将改进现有的模型。实现了不同条件下的腐蚀试验，建立了模型。通过使用参数来描述缺陷的形状和分布，将对每个样品的点蚀进行量化。使用微光学3D图案表面测量装置，缺陷的表征将是非破坏性的。随后进行了拉伸试验的有限元模拟，得到了缺陷形状、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。这将通过加权系数来实施。最后，根据解析关系和权重因子，得到了剩余强度模型。独立的材料折减系数将通过将当前损伤状态的计算强度与未腐蚀材料的强度相关联来计算。因此，预测残余强度的模型可以应用于更多的铝合金。

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.