Microstructural characteristics and bending properties of extruded SEN9 and SEN11 magnesium sheets

Abstract

Mg–Al-based alloys with small amounts of Ca and Y, referred to as stainless, environment-friendly, nonflammable (SEN) alloys, exhibit significantly improved resistance to corrosion and ignition compared to commercial Mg alloys. This study investigates the microstructural characteristics and bending properties of extruded sheets of Mg–(9, 11)Al–1Zn–0.3Mn–0.3Ca–0.2Y alloys (SEN9 and SEN11). These sheets contain particles containing Ca or Y, such as Al2Y, Al2Ca, Al8Mn4Y, and Al–Ca–Zn phases, along with dynamically precipitated Mg17Al12 particles. In the SEN9 sheet, Mg17Al12 particles are distributed in a band-like pattern along the extrusion direction, whereas in the SEN11 sheet, a more uniform distribution of abundant Mg17Al12 particles is observed. In both sheets, a macrocrack initiates on the bottom surface of a specimen and propagates into the specimen at an angle of approximately 35° during three-point bending tests. The SEN11 sheet exhibits a higher bending yield strength (by 27%) than the SEN9 sheet, primarily due to the stronger grain-boundary and particle hardening effects in the former, resulting from finer grains and a greater number of particles. In the SEN9 sheet, sharp deformation twins and subsequent cracks along these twins are formed during bending. Meanwhile, in the SEN11 sheet, the numerous Mg17Al12 particles induce stress concentration during bending, ultimately leading to premature bending failure before the formation of twins. As a result, the SEN11 sheet exhibits a 59% lower bending formability compared to the SEN9 sheet.