Abstract: The microstructures and wear resistance of Al-20%Si and Al-30%(Mass fraction)Si alloys solidified under different cooling rate have been researched. Results of experiments indicates that effects of the cooling rate on solidification microstructures and wear resistance of alloy are significant. When cooling rate increases,the phase constitution of solidification microstructure and the shape and sizes of primary silicon crystal in the microstructure of Al-20%Si and Al-30%Si alloys change obviously. The solidification microstructures both of the specimen solidified in furnace of which the cooling rate is less than 0.1K/s and the specimen solidified in refractory mold of which the cooling rate is less than 1K/s are composed of (α+Si) eutectic and primary Si crystal, and the coarse plateshaped primary Si crystal and needle-shaped eutectic Si crystal are inspected in the solidification microstructure. The solidification microstructures of the specimen solidified in metal mold of which the cooling rate is about 10K/s is composed of (α+Si) eutectic and primary Si crystal and the dendritic α phase, and the shape of primary Si crystal is plate or block, the eutectic Si crystal is also needle-shaped, the dendritic α phase emerged in the metal mold casting specimen. The solidification microstructures of the over-spray powder cooled by (104~106)K/s is also composed of (α+Si) eutectic and primary Si crystal and the dendritic α phase, and the shape of most of primary Si crystals are fine block. The solidification microstructures both of spray formed Al-20%Si alloy and Al-30%Si alloy are composed of Si crystal and α phase, the fine Si crystals are well-distributed in the α phase matrix. With increasing cooling rate, the size of silicon crystal diminished, the wear resistance of Al-20%Si alloy and Al-30%Si alloy increases significantly due to the wear mechanism of alloy changed.
Effects of cooling rate on solidification microstructures and wear resistance of hypereutectic Al-Si alloy
Abstract:
The microstructures and wear resistance of Al 20%Si and Al 30% (Mass fraction) Si alloys solidified under different cooling rate have been researched. Results of experiments indicates that effects of the cooling rate on solidification microstructures and wear resistance of alloy are significant. When cooling rate increases, the phase constitution of solidification microstructure and the shape and sizes of primary silicon crystal in the microstructure of Al 20%Si and Al 30%Si alloys change obviously. The solidification microstructures both of the specimen solidified in furnace of which the cooling rate is less than 0.1?K/s and the specimen solidified in refractory mold of which the cooling rate is less than 1?K/s are composed of ( α +Si) eutectic and primary Si crystal, and the coarse plate shaped primary Si crystal and needle shaped eutectic Si crystal are inspected in the solidification microstructure. The solidification microstructures of the specimen solidified in metal mold of which the cooling rate is about 10?K/s is composed of ( α +Si) eutectic and primary Si crystal and the dendritic α phase, and the shape of primary Si crystal is plate or block, the eutectic Si crystal is also needle shaped, the dendritic α phase emerged in the metal mold casting specimen. The solidification microstructures of the over spray powder cooled by (10 4~10 6) K/s is also composed of ( α +Si) eutectic and primary Si crystal and the dendritic α phase, and the shape of most of primary Si crystals are fine block. The solidification microstructures both of spray formed Al 20%Si alloy and Al 30%Si alloy are composed of Si crystal and α phase, the fine Si crystals are well distributed in the α phase matrix. With increasing cooling rate, the size of silicon crystal diminished, the wear resistance of Al 20%Si alloy and Al 30%Si alloy increases significantly due to the wear mechanism of alloy changed.
Fig.2 Solidification microstructures of hypereutectic Al-Si alloys (a) —Al-30%Si alloy solidified in the furnace; (b) —Al-30%Si solidified in refractory mould; (c) —Al-20%Si alloy solidified in metal mould; (d) —Al-30%Si alloy solidified in metal mould; (e) —Al-30%Si over-spray powder; (f) —Al-30%Si spray formed billet
Fig.3 SEM photographs of wear surface of hypereutectic Al-Si alloys (a) —Al-30%Si alloy solidified in refractory mould; (b) —Al-20%Si alloy solidified in metal mould; (c) —Al-20%Si alloy spray formed; (d) —Al-30%Si alloy spray formed