Study on Rapidly Solidified Powder Magnesium Alloys

为改善传统镁合金材料的性能，在AZ 91和ZK 61镁合金中添加Si、Ni、Mn和Ce，制备了快速凝固粉末冶金材料，并对其力学性能进行了测试。快速固化的薄片显示出平均单元尺寸为1至2 μ m的蜂窝状树枝状结构。凝固过程中的冷却速率估计为10^4至10^5 K/s。采用冷压-热挤压工艺制备了直径为7 mm的粉末冶金材料，在所制备的AZ 91基合金粉末冶金材料中，含Si合金在433 K时效时的峰值硬度最高。含Ni和Ce的合金对AZ 91和ZK 61基合金都表现出很小的时效硬化。含锰ZK 61合金在403 K时的时效硬化程度高于基体合金。研究表明，采用快速凝固技术，适当添加合金元素，可以有效地提高镁合金的强度。在所有试验材料中，添加Ce的ZK 61合金粉末冶金材料的抗拉强度最高，达到554 MPa。该合金的比强度高达295 MPa，超过了7075铝合金和Ti-6Al-4V。在高温下，快速凝固的粉末冶金材料显示出较低的抗拉强度和较高的伸长率比I/M镁材料。AZ 91镁合金粉末冶金材料在573 K时的延伸率大于400%，处于超塑性变形区。因此，快速凝固镁粉末冶金材料的显著特征是比常规加工的镁材料具有更高的室温强度和更高的高温延展性。

Rapidly solidified P/M materials were produced for AZ91 and ZK61 magnesium alloys with alloying additions of Si, Ni, Mn and Ce, and their mechanical properties were examined, with the prupose of improving properties of conventionally processed magnesium materials. Rapidly solidified flakes showed cellular dendritic structures of 1 to 2 mum in the average cell size. The cooling rate during solidification was estimated as 10^4 to 10^5 K/s. P/M materials of 7 mm in diameter were produced by cold pressing and hot extrusion.Among obtained P/M materials of AZ91 based alloys, Si bearing alloy showed the highest peak hardness when aged at 433 K. Ni and Ce bearing alloys showed very little age hardening for both AZ91 and ZK61 based alloys. Mn bearing ZK61 alloy showed higher age hardening at 403 K than the base alloy. Rapid solidification of magnesium alloys with some proper alloying additions was shown to be very effective in increasing strength of magnesium alloys. Among the all tested materials, P/M materials of Ce added ZK61 alloy showed the highest tensile strength of 554 MPa. The specific strength of this alloy was as high as 295 MPa and exceeded those of 7075 aluminum alloy and Ti-6Al-4V. At elevated temperatures, rapidly solidified P/M materials showed lower tensile strength and higher elongation than I/M magnesium materials. P/M materials of AZ91 alloy showed elongation higher than 400% at 573 K, which is in the superplastic deformation regime. Thus, the salient features of rapidly solidified magnesium P/M materials are higher strength at room tempearture and higher ductility at elevated temperatures than the conventionally processed magnesium materials.