지르코늄 첨가에 따른 Al-Si-Cu합금의 미세조직 및 열처리 특성

Abstract

In this study, the effect of adding zirconium to commercial Al-Si-Cu alloys on the changes in microstructure and mechanical properties of the alloy was investigated. Test specimens with 0.2, 0.4, 0.8 and 1.0 wt% zirconium were prepared by gravity casting of the commercialized Al-12Si-2Cu, Al-6Si-2Cu, and Al-10Zr master alloys. The gravity casting alloy was subjected to solution treatment at 495℃ for 4 hours and then aged at 190℃ for 5hours. In order to observe the change in hardness of the alloy through long-term aging treatment, The aging treatment was performed for 2, 5, 8, 16, 24, and 48 hours after solution treatment. The secondary dendrite arm spacing (SDAS) of the alloy increased as the amount of Zr addition increased, and the primary (Al,Si)3(Zr,Ti) phase was observed by FE-SEM EDX. As for the mechanical properties of the alloy, The hardness and strength decreased with increase in SDAS. Precipitation of the Zr-rich phase on the Al matrix after T6 heat treatment was observed by EPMA, FE-SEM EDX, and XRD bulk-extraction. In addition, it was found to be (Al,Si)3Zr phase, which Al atoms ard partially replaced by Si atoms. The (Al,Si)3Zr phase existed in two forms, spherical and plate-like shape. As a result of FFT pattern analysis for their crystallographic structure analysis, the sperical Zr-rich phase was a cubic structure, and the plate-like Zr-rich phase was a tetragonal structure. Precipitation of the Zr-rich phase increased the hardness and strength of the alloy. Consequently, The generation of Zr-rich phase with the addition of Zr in Al-Si-Cu alloy would be a successful resistance to the overaging phenomenon in Al alloy.