Multi-scale investigation of A356 alloy with trace Ce addition processed by laser surface remelting

Abstract

Laser surface remelting (LSR) has shown great application potential in Al-Si alloy parts (e.g., surface strengthening, surface repairing). However, the microstructural details and properties of LSR-treated hypoeutectic Al-Si alloy remains to be investigated. In this work, the microstructure of an Al-7Si alloy with adding 0.05 wt% Ce fabricated by LSR was studied through multi-scale characterization. Three regions with distinct morphologies after LSR were obtained: i) the remelting zone (RMZ) including an equiaxed grain region and a columnar to equiaxed transition (CET) region; ii) the heat-affected zone (HAZ) with segregation of Si; iii) substrate zone (SZ). Nanoscale eutectic Si particles were observed in RMZ and HAZ. Moreover, it is confirmed for the first time that the Ce atom can absorb on the {111}Si planes and leads to high density of twins and stacking faults. After LSR, the increased microhardness of RMZ is mainly attributed to the precipitation and dislocation strengthening. By further T6 heat treatment, the microhardness of RMZ increases to 126 HV. Dispersed small Si particles decrease the critical stress of crack propagation. Additionally, the high density of twins, stacking faults and Al-rich clusters within Si particle plays a significant role in toughness improvement.