Microstructure and mechanical response of A206 alloy processed by ultrasonic spray-assisted polymer derived ceramic reinforcement

The work presents the first application of an ultrasonic spray-assisted in-situ processing to strengthen A206 Al – Cu alloy with PDC particles. An atomized liquid polysiloxane precursor was directly injected into the melt, where rapid pyrolysis produced sub-micron-sized SiOC particles (0.3–1 µm) homogeneously distributed with clean particle – matrix interfaces. The existence of these particles facilitated heterogeneous nucleation and dendrite fragmentation, decreasing the α-Al grain size from ~92 ± 5 µm to ~58 ± 3 µm (~37% decrease) and making finer the interdendritic CuAl2 phase. Mechanical testing indicated substantial improvements in hardness (118 ± 2 HV → 146 ± 3 HV, +24%), yield strength (155 ± 3 MPa → 172 ± 4 MPa, +11%), and ultimate tensile strength (270 ± 5 MPa → 310 ± 6 MPa, +15%), with ductility reducing by a very small margin (7.2% → 6.1%). In comparison with standard PDC + stir casting, which gave only modest improvements because of dispersoid clustring, the spray-assisted process yielded superior strengthening and homogeneity. Results confirm ultrasonic spray-assisted precursor delivery as a contamination-free, scalable, and efficient processing method for the fabrication of high-performance Al – ceramic composites, with opportunities for further optimization towards elevated-temperature applications.