Journal
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE
Volume 25, Issue 12, Pages 5530-5539Publisher
SPRINGER
DOI: 10.1007/s11665-016-2397-5
Keywords
Cu addition; hot tearing; mechanical properties; Mg alloys; microstructure
Categories
Funding
- General project of scientific research of the Education Department of Liaoning Province [L2015397]
- National Natural Sciences Foundation of China [51504153, 51571145]
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The microstructures and mechanical properties of Mg-6Zn-xCu-0.6Zr (x = 0, 0.5, 1, 2, 3 wt.%) alloys are investigated. The effect of Cu additions on the hot-tearing susceptibility (HTS) of Mg-6Zn-0.6Zr is also studied using constrained rod casting apparatus equipped with a load cell and data acquisition system. The experimental results indicate that 0.5wt.% Cu addition into the Mg-6Zn-0.6Zr alloy shows the optimum comprehensive properties, i.e., a combination of high strength, high hardness, high hot-tearing resistance and excellent ductility. However, when Cu content reaches 2 and 3wt.%, the deterioration in mechanical properties observed is attributed to the increment in coarsened MgZnCu phase and the continuous networks of intergranular phases in these two alloys. The Cu-free base alloy had a high HTS, which is attributed to its large vulnerable temperature range and coarse grain structure, which easily caused tear propagation. In contrast, the Cu-contained alloys exhibited low HTS are due to their narrow vulnerable temperature ranges and its refined equiaxed grain structure, which effectively accommodated the stress developed during solidification. The hot-tearing fracture surfaces indicate that the hot-tearing initiated and propagated along the grain boundaries with liquid films. The results also suggest that the hot-tearing resistance can apparently be improved by increasing the initial mold temperature.
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