MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Mg-1.7Y-1.2Zn SHEET PROCESSED BY HOT ROLLING AND FRICTION STIR PROCESSING

摘要

The use of lightweight structural materials is an integral part of mass reduction strategy in transportation applications. Magnesium based sheet products have gained significant interest in the automobile industry. Newer magnesium alloys such as Mg-Y-Zn have potential to develop sheet products with superior mechanical properties owing to improved precipitation hardening response. In the present work, rolled sheet of an Mg-1.7Y-1.2Zn alloy containing small amounts of Al and Ce was investigated. Microstructure and mechanical properties were examined in as-rolled, rolled+aged, friction stir processed (FSP) and FSP+aged conditions. Mechanical properties (YS, UTS and %El) of the sheet showed certain anisotropy in rolling and transverse directions, which was marginally reduced upon ageing. However, FSP led to a significant range of mechanical properties depending on the test direction. Ageing of the FSP sheet showed improvement in mechanical properties and reduced anisotropy in the two directions. The static recrystallization due to ageing caused reduced anisotropy in FSP treated sheet. The overall strength-ductility variation is discussed in terms of relative contributions of grain boundary strengthening, texture and precipitation strengthening.