Effect of single-step hot isostatic pressing & solution treatment on the microstructure of Al-Cu-Mg-Ag-Ti-B (A205) alloy processed by laser powder bed fusion

Hot isostatic pressing (HIP) is increasingly used as a post-processing technique for components produced via laser powder bed fusion (LPBF). However, the microstructural evolution of the as-HIPed condition, particularly in precipitation-hardening alloys, remains largely unexplored. This study investigates the as-HIPed microstructure of a precipitation-hardening Al-Cu-Mg-Ag-Ti-B (A205) alloy processed by LPBF. A combined HIP & solution treatment (HIP-Quench) was performed in a single-step to evaluate the effectiveness of HIP in promoting the dissolution of secondary phases. The HIP cycle involved a controlled ramp rate (7 °C/min) to the desired solution temperature, a 1-hour hold at 100 MPa, followed by quenching. Solution temperatures of 530 °C and 540 °C were examined. For a comparison, an equivalent non-HIP cycle with various interruptions was conducted. Preliminary assessments revealed a reduction in porosity from 0.23 % in the as-built condition to 0.05 % and 0.07 % in the as-HIPed conditions. Microstructural analysis indicated that, despite HIP-Quench being conducted at different solutioning temperatures, the complete dissolution of the θ-Al₂Cu phase was not achieved. Furthermore, signs of incipient melting along the grain boundaries were noticed in both HIPed samples but were absent in the non-HIPed samples. The findings suggest that HIP treatment induces re-precipitation of the blocky θ-Al₂Cu phase along the grain boundaries, which subsequently undergoes interfacial premelting.