Investigations on Hot Tearing Behavior of Mg-7Zn-xCu-0.6Zr Alloys
Ye ZHOU,Pingli MAO(),Zhi WANG,Zheng LIU,Feng WANG
School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, China
Cite this article:
Ye ZHOU,Pingli MAO,Zhi WANG,Zheng LIU,Feng WANG. Investigations on Hot Tearing Behavior of Mg-7Zn-xCu-0.6Zr Alloys. Acta Metall Sin, 2017, 53(7): 851-860.
As one of the highest temperature magnesium alloys, Mg-Zn-Cu ternary alloys are draw much attention in recent years. However, the previous investigations were mainly focused on their microstructure and mechanical properties. The investigations on their solidification and hot tearing behaviors are barely discussed. In order to improve the industrial applications of Mg-Zn-Cu alloy, it is necessary to better understand the solidification pathways, phase constituent and hot tearing susceptibility (HTS) of these alloys. In this work, the effect of Cu additions on the hot tearing behaviors of Mg-7Zn-xCu-0.6Zr (x=0, 1, 2, 3) alloys was studied using with T type hot tearing mold. The microstructure and the morphology of cracking zone of Mg-7Zn-xCu-0.6Zr (x=0, 1, 2, 3) alloys were observed by XRD and SEM, respectively. The hot cracking susceptibility of Mg-7Zn-xCu-0.6Zr (x=0, 1, 2, 3) alloys were characterized by the measurement of crack volume. The experimental results show that the grain sizes of Mg-7Zn-0.6Zr alloys were refined by addition of Cu element. Meanwhile, the amount of eutectic phase was increased with increasing the Cu content and the separated dendritic was refilled by the eutectic phase. Hot tearing susceptibility of Mg-7Zn-0.6Zr was decreased with increasing of Cu content. The Mg-7Zn-0.6Zr and Mg-7Zn-1Cu-0.6Zr alloys were completely broken. The hot cracks of Mg-7Zn-xCu-0.6Zr (x=0, 1, 2, 3) alloys were formed by liquid film, solidification shrinkage and interdendritic bridge.
Fund: Supported by National Natural Science Foundation of China (Nos.51504153 and 51571145) and General Project of scientific research of the Education Department of Liaoning Province (No.L2015397)
(a) whole setup (b) thermocouple position for detecting onset of hot cracking during casting (unit: mm)
Fig.2 Definition schematic diagram of dendritic coherence temperature and dendritic coherence solid fraction (Inset shows the high magnified curves. Tc—melt center temperature, Te—melt edge temperature, ΔT—melt center and edge temperature difference)
Alloy
Tcoh / ℃
fscoh
Mg-7Zn-0.6Zr
619.1
0.32
Mg-7Zn-1Cu-0.6Zr
610.6
0.39
Mg-7Zn-2Cu-0.6Zr
599.6
0.51
Mg-7Zn-3Cu-0.6Zr
598.9
0.57
Table 1 Dendritic coherence temperature (Tcoh) and dendritic coherence solid fraction (fscoh) of Mg-7Zn-xCu-0.6Zr (x=0, 1, 2, 3) alloys
Fig.6 Contraction force and temperature as function of time in Mg-7Zn-xCu-0.6Zr alloy with x=0 (a), x=1 (b), x=2 (c) and x=3 (d) (fs—solid fraction)
Fig.7 OM images of Mg-7Zn-xCu-0.6Zr alloys with x=0 (a), x=1 (b), x=2 (c) and x=3 (d)
Fig.8 Grain sizes of Mg-7Zn-xCu-0.6Zr (x=0, 1, 2, 3) alloys
Fig.9 SEM images of the hot tearing fracture surface of Mg-7Zn-xCu-0.6Zr alloy with x=0 (a), x=1 (b), x=2 (c) and x=3 (d)
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