Monitoring Failure Sequence in Cold-Sprayed Al6061 Deposits Using Acoustic Emission

Cold spray (CS) is a recent addition to the thermal spray family with extensive research conducted on the effects of different process parameters during CS deposition various metallic powders. While mechanical and fatigue strengths of cold-sprayed deposits have been evaluated through static and dynamic testing, identifying the sequence of failure mechanisms—whether cracks within the coating occur before delamination at the coating–substrate interface—remains visually challenging but crucial for pinpointing weak points within the deposit. To address this, acoustic emission (AE) testing was employed in this study to reliably determine the failure sequence through in situ monitoring. Using a four-point bending setup, a 2.5-mm-thick Al6061 coating on an Al6061-T6 substrate was analyzed in real time with AE data and video correlation. The findings revealed that cracks associated with higher AE frequencies (≥ 100 kHz) appeared first, accompanied subsequently by delamination, which was correlated with lower-frequency AE events (< 100 kHz). This AE methodology shows promise for integration with other static tests, such as open-hole tension as well as fatigue testing to determine similar failure sequences. By providing a clear understanding of failure mechanisms, this approach advances the structural evaluation of cold-sprayed deposits and their potential applications.