Microstructure And Phase Composition Of Directionally Solidified Ternary Al-Cu-Ni Alloy

Nowadays, the investigation of the solidification theory is mainly focused on the directional solidification which is based on binary aluminous alloy. But the researcher rarely studied the directional solidification of ternary or multiple aluminum alloys. In this paper, ternary Al-Cu-Ni alloy was chosen with down-drawing directional solidification. We studied the effects of different down-drawing rate on the directionally solidified microstructure.The alloy composition selected was Al-18wt%Cu-5wt%Ni. The temperature gradient which was the experiment conditions of directionally solidified Al-Cu-Ni alloy after smelted was 5 K/mm. The down-drawing rates were 1 mm/min, 5 mm/min, 10 mm/min, 20 mm/min. Optical Microscope (OM) and Field Emission Scanning Electron Microscope (FESEM) were used to preliminarily understand the as-cast microstructure and the phase composition of the ternary Al-Cu-Ni alloy on the cross section and the longitudinal section. X-Ray Diffractomer (XRD) which was combined with the method of Material-Studio simulative software was used to eventually determine the ternary phase of the ternary Al-Cu-Ni alloy and conclude the crystal structure of each generating phase. Differential Scanning Calorimeter (DSC), FESEM, Energy Dispersive Spectrdmeter(EDS) and XRD were used to preliminarily determine the generating phases and the element composition of the directionally solidified ternary Al-Cu-Ni alloy and further determine preferred orientation of the crystal in the generating phases.The experiment also detailedly analyzed the effects of different down-drawing rates on the directionally solidifide microstructure. OM and FESEM were used to observe the microstructure on the cross section and the longitudinal section of directionally solidified samples. The results showed that the growth of the microstructrue in the directionally solidified alloy is in the same direction as heat flow. At the same temperature gradient, the array of the directionally solidified microstrutures is more symmetrical and well-regulated with the decrease of down-drawing rates, and the structures are changed from the celluler to the dendrite, and the microstructure is increasingly refined.