Characterization of Brittle Phase in Magnesium Based Materials Prepared by Powder Metallurgy

Abstract

Magnesium-zinc based materials are characteristic with the creation of intermetallic phases, strongly influencing material mechanical properties. Mg-Zn powder mixture (10 % wt. Zn) was processed by the hot pressing method under 500 MPa at 300 °C. Microstructure of the prepared material was analyzed in terms of light optical microscopy and scanning electron microscopy. Chemical and phase composition of the processed material were analyzed by energy-dispersive X-ray spectroscopy and X-ray powder diffraction, respectively. Microhardness testing was adopted to characterize created structure mechanical properties on the microscopic level. Depending on the Mg-Zn powder mixture local chemical composition, the structural and chemical analysis of the processed material revealed that it consisted of magnesium and zinc rich areas, and MgZn2 intermetallic phase. The MgZn2 intermetallic phase belongs to the so-called Laves phases group with the general formula AB2. Laves phases are characteristic with high hardness and the related high brittleness. Their presence in the material usually results in deterioration of mechanical properties such as strength and toughness. The microhardness of magnesium and zinc rich areas in the processed material was 58±1 HV 0.025 and 47 ±1 HV 0.025, respectively, while the value of the microhardness for MgZn2 intermetallic phase was 323±12 HV 0.025. Different behavior and mechanical properties of the present phases was observed on the fracture surfaces of specimens broken during the 3-point bend test. While brittle fracture was a characteristic feature for MgZn2 intermetallic phase, the rest of the material exhibited more ductile fracture behavior with characteristic transgranular failure.