Influence of Al2Cu morphology on the incipient melting characteristics in B206 Al alloy

Prevention of incipient melting during solution heat treatment is critical for precipitation hardenable alloys such as B206, since it is deleterious to mechanical properties. For this reason, hot-stage laser scanning confocal microscopy (LSCM) was used for in-situ characterization of incipient melting of blocky Al2Cu and Al-Al2Cu eutectic during transient heating of B206 Al alloy to determine the mechanisms of melting. Microstructural analysis was carried out prior to and following the LSCM experiments using SEM and EDX. The results suggest that the blocky Al2Cu particles gradually developed a rough surface comprised of small spheres of locally melted material in small regions around the particle, followed by complete particle melting. In contrast, the globular Al-Al2Cu eutectic clusters melted completely which was followed by a rapid propagation of liquid film on the sample surface. Following incipient melting, the microstructure consisted mainly of coarse Al-Cu bearing eutectic, small quantities of blocky Al2Cu particles and oxides along grain boundaries.