Ag, Co, and Ge additions in Be–Al alloys: Correlation between microstructural evolution and strengthening mechanisms

In this study, Be-Al and Be-Al-Ag-Co-Ge alloys were fabricated by investment casting, and the effects of Ag, Co and Ge elements on the microstructure and mechanical properties were investigated. The results demonstrated that the addition of Ag, Co and Ge reduced the secondary dendritic arm spacing of Be, leading to a morphological transition of the Be phase from columnar dendrites to spherical equiaxed grains. Concurrently, Ag and Co atoms diffused toward the Be/Al interface driven by interface energy minimization, forming segregations that enhanced the interface adhesion work and consequently improved the Be/Al interface bonding strength and mechanical properties of the Be-Al alloy. In addition, uniformly distributed Ag 2 Al nanoparticles were formed within the Al phase. Compared to the Be-Al alloy, the Be-Al-Ag-Co-Ge alloy exhibited enhanced mechanical properties, with yield strength of 228.2 MPa, ultimate tensile strength of 272.3 MPa, and Vickers hardness of 115.72 HV, representing increases of 106.07%, 85.87% and 97.67% respectively. The strengthening mechanism of the Be-Al-Ag-Co-Ge alloy was analyzed using a theoretical model, revealing that Ag 2 Al precipitates dominate the yield strength enhancement, contributing 50.78 MPa primarily through Orowan, GND, and CTE mismatch strengthening. This work provides an effective strategy for optimizing the microstructure and enhancing the mechanical properties of Be-Al alloys.