Microstructural characteristics and formation mechanism of friction stir welds of SiC particulates reinforced Al–Si matrix composites

• An unusual melting phenomenon was observed in the friction stir welds.
• The formation mechanism of microstructural characteristics was revealed.
• Fined α-aluminum and eutectic silicon were formed in the friction stir welds due to the rapid cooling during the solidification.
• The eutectic silicon looked like needle shape in the retreating side and equiaxed shape in the advancing side.

The aluminum alloy matrix was partially melted and α-aluminum dendrites and eutectic silicon occurred in the friction stir weld. The eutectic silicon looked like needle shape in the retreating side and equiaxed shape in the advancing side. The formation mechanism of microstructural characteristics is divided into four stages, including the melting of matrix and cracking of coarse SiC particles, the nucleation of α-aluminum, the growth of α-aluminum and nucleation of eutectic silicon, and the formation of fine eutectic silicon.