Effect Of Al Addition On The Microstructure And Properties Of Mg-Y-Zn-Mn Alloy Reinforced With LPSO Phases

Magnesium alloy have been widely used in the areas such as automobile transportation,aerospace,and commercial electric products because of its excellent machining performance and good damping properties,low density,high specific strength and good stiffness.It is regarded as the most potential structural metal materia in the 21 century and one of the hotspots in the material research both at home and abroad.Due to their high strength and ductility,good properties of corrosion and heat resistance,rare earth containing Mg alloys have been an important part of commercial magnesium alloys.And the discovery of long period stacking ordered?LPSO?structure which can further improve the mechanical properties of RE magnesium alloys have attracted widely interest of researchers.In this study,Mg-Y-Zn-Mn-Al alloys with LPSO structure were prepared by traditional casting method.An in-situ composite strengthening phase was found in the ?-Mg matrix.Methods such as solidsolution heat treatment and direct extrude deformation methods were used to research the solid-solution heat treatment tine,cooling process and the extrusion speed on the microstructure and mechanical properties of Mg_93.6Y_2.5Zn_2.5Al_0.4 alloy.Effect of Al addition on the transition between 18 R and 14 H LPSO phases.The electronical corrosion resistance at different conditions were also discussed.Main results of this study are listed as following:?1?Al can refine the ?-Mg matrix,reducing the distance between the dendrites.This element can reduce the volume fraction of LPSO phase and precipite a new ternary composite strengthening Al?Y,Zn?₂ phase on the matrix.When the Al addition was 0.4at%,the volume fraction radtio between LPSO and Al?Y,Zn?₂ phase is the most appropriate and the tensile strength and elongation reached a peak value of 259 MPa/5.4%.?2?The moderate solidsolution treatment temperature was 500 ?.After furnace cooling,the continuous network W phase was spheroidized;block 18 R LPSO phase along the grain boundary transformed into 14 H LPSO phase which homogeneously distributed in the grain matrix;the Al?Y,Zn?₂ phases changed into fishbone-like structure from rod-like and needle-like in the as cast condition.?3?Al?Y,Zn?₂ phase is very sensitive to the heat treatment time.After a small period of solid solution time,they became gathered,which will reduce the tensile strength of the alloy.The moderate solid solution time was 30 h and the tensile strength and elongation was 357 MPa and 10.5%.?4?Direct extrude treatment had a significant effect on the microstructure and mechanical properties of Mg_93.6Y_2.5Zn_2.5Al_0.4.When the extrude speed is 30mm/min,the Al?Y,Zn?₂ phase was extruded into small particles and distributed dispersive in the alloy.In addition,the LPSO phases were bended with small kinking angles due to the severe plasticity deformation.Meanwhile,the volume fraction of DRX is the biggest.