Microstructure and Properties of Multi-Al-Si Casting Alloy with Cooling Rate

Abstract

Near-eutectic Al-Si multi-component alloy has broad application prospects in automotive, aerospace and military fields, and the microstructure of the alloy could be effectively improved by changing the cooling rate of the alloy. In this paper, Al-11.5Si-4Cu-2.7Ni-Mg-0.45Fe alloy was obtained by rapid solidification and water-cooled copper casting technique, and analyzed by metallographic microscope (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The effect of two cooling rates on the microstructure and microhardness of the alloy were studied. The results showed that the hardness of the rapid solidification sample was increased by 32.22% compared to that of the water-cooled copper casting sample. In addition, the water-cooled copper casting significantly reduced the size of the primary silicon in the microstructure of the alloy compared with the conventional metal casting. The element distribution of the rapidly solidified annealed sample was more uniform than that of the water-cooled copper mold, the microstructure of the rapid solidification sample consisted of equiaxed α-Al dendrites and a small amount of amorphous phase, and there was no obvious solidification and precipitation of AlCuNi phase, especially no precipitation of significant Si phase. Moreover, the content of Fe in the samples of rapid solidification was larger at different positions, while the content of Mg, Ni and Cu was not much different, which was related to the lattice structure of different metal elements. The extreme positions of the peaks of the aluminum phase of the rapidly solidified lanthanum were shifted to the left relative to the water-cooled copper mold, that was, the diffraction had a small angular shift, which was related to the over solid solution of the alloying elements.