Abstract

A novel solid-state additive manufacturing process, Additive Friction Stir-Deposition (AFS-D), provides a new path for additively repairing damaged non-weldable aerospace materials that are susceptible to induced thermal gradients within the microstructure. In this work, we quantify the microstructural evolution and mechanical performance of an additively repaired AA7075-T651 (Al-Zn-Mg-Cu) via the AFS-D process. To evaluate the AFS-D process for repairing high strength aluminum alloys, the AFS-D technique was used to additively fill a linear groove that was machined into an AA7075-T651 plate. After repairing the plate with the AFS-D process, the repaired plate was subjected to standard T6 heat treatment. The results of this study show that the heat-treated AFS-D repair did not exhibit any significant grain growth and demonstrated an increase in the average Vickers hardness in the repair compared to the wrought 7075-T651 control. Tensile and fatigue behavior was investigated for heat-treated repair and compared to the wrought AA7075-T651 control. The heat-treated repair exhibited wrought-like tensile properties for yield stress and ultimate stress, however the heat-treated repair had significant scatter in the elongation to failure. Additionally, the mean fatigue behavior of the heat-treated repairs displayed a reduction in cycles to failure compared to the wrought control. Lastly, a microstructure-sensitive fatigue life model was employed to elucidate process-structure-property fatigue mechanism relations of the heat-treated repair and wrought AA7075.

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