Abstract
The strength of magnesium alloys can be effectively increased by refinement of crystal grain size. This study was made to investigate the strength of Mg-Al-Zn-Ca alloys processed with friction stir processing (FSP), which is a method for refining crystal grains. The relationship between mechanical properties and process conditions was investigated. The grain size became finer and more uniform by FSP. The hardness of the FSPed material tends to decrease slightly compared to that before processing. As for tensile properties, FSP processing decreased the value of 0.2% proof stress, and plastic deformation started at lower stress in FSPed specimens. However, the ductility was improved by FSP. In this study, specimens processed with high-pressure torsion (HPT), was also studied. The grain size of the specimens was significantly refined by HPT, and the relation between hardness and grain size followed the Hall-Petch relation, indicating that grain size reduction is effective in increasing the strength of Mg-Al-Zn-Ca alloys used in this study. The effect of change in crystal orientation on the strength required for plastic deformation is also discussed.
