Effect of Ball-Milling on the Microstructure of Mg-4Al-2RE Alloy Prepared by Spark Plasma Sintering

摘要

Samples of magnesium alloy Mg-4Al-2RE were prepared by the Spark plasma sintering method from gas-atomized and ball-milled powder. The samples were sintered at temperatures in a range of 400-500°C. The effect of sintering temperature on the microstructure and mechanical strength was investigated by scanning electron microscopy including electron backscattered diffraction (EBSD) and microhardness measurement. It was found that ball-milling had a significant effect on the microstructure of the powder and consequently on the densified material as well. In addition, the sintering temperature influences significantly both the grain structure and the secondary phases distribution in the compacted samples. The application of a relatively high load during sintering caused partial deformation of the individual particles. Consequently, recrystallization occurred, especially along former particle boundaries. Samples sintered from the ball-milled powder exhibited a more homogenous distribution of much smaller grains, because of the additional deformation induced during the milling. An increase in the sintering temperature resulted in pronounced grain growth and dissolution and globularizatrion of the secondary phases. A deterioration of the fine-grained microstructure, and consequently mechanical strength, was much slower appeaing in samples prepared from ball-milled powder.