Effects Of Al Additions On Microstructure And Mechanical Properties Of Mg-Y-Ca-Mn Alloy

Precipitation-hardenable Mg-Y based alloys have received extensive attention in recent years due to their excellent mechanical properties.When the content of Y in the Mg-Y-based alloy is less than 8 wt.%,the precipitation strengthening response becomes worse.In this paper,the effects of Al additions on the microstructure of Mg-7Y-0.6Ca-0.5Mn alloy were studied using scanning electron microscopy(SEM),scanning transmission electron microscopy(STEM),and X-ray energy spectroscopy(EDS),and the mechanical properties were tested by Micro hardness tester and tensile testing machine.Meanwhile,the relationship between the microstructure and mechanical properties was discussed.SEM and TEM research results show that the number density of intermetallic particles increased with an increase in Al content.Al additions also led to the formation of lath and square Al₂Y particles,and the distribution of Mn was observed in them.The morphology and size of the Al₂Y particles would change during the heat treatment,and its occurrence could obviously refine grain sizes.But the formation of Al₂Y particles consumed Y element,thus the addition of Al decreased the age-hardening response of Mg-7Y-0.6Ca-0.5Mn alloy.The precipitate phases in peak-aged Mg-7Y-0.6Ca-0.5Mn-1Al consist of the novel basal precipitate phase,Mg₂Ca,Al₂Y and?'phase,and prismatic?'phase.The distributions of Y?Ca and Y?Al were respectively observed in novel basal precipitate phase and?'phase.With the addition of Al,the grain sizes of as-extruded Mg-7Y-0.6Ca-0.5Mn-x Al alloys were significantly reduced,the finest grain size is about 3(?)m,which occurred in Mg-7Y-0.6Ca-0.5Mn-1Al alloy,and the plasticity and toughness of alloys were enhanced.The Mg-7Y-0.6Ca-0.5Mn-1Al extrusion alloy has excellent comprehensive mechanical properties with yield strength 249 MPa,ultimate tensile strength 310.51MPa and the elongation 20.33%.