Strengthening And Toughing Rules Of Mg-gd-y Alloy

As everyone knows,magnesium alloy has the shortcomings of low strength,poorplasticity,bad imputrescibility and weak performance at elevated temperature,althoughit has a lot of advantages. From the angle of improving the strength and toughness of themagnesium alloy, the microstructure and mechanical properties of as-cast,extruded andextruded-T5 Mg-15Gd-3Y alloy were investigated, and certain meaningful conclusionswere obtained.First of all, the microstructure of the as-cast state was dendrity, with the main phaseof Mg solid solution and Gd,Y eutectic particles at grain boundaries. The optimal solidsolution parameter was 480℃/4h, with the grain boundaries straighted and grains grownup.The rare-earth concentrated and spheroidized, and eutectic remelting were discoveredwith the rising of temperature and prolonging of ageing time. Tensile strengthes of the ascast,cast-T4 and cast-T6 alloy were 156.5,206and 257 Mpa, and elongations of themwere1.5%,3.2%,3.84%.Secondly,Mg-15Gd-3Y alloy was extruded. Recrystallization happened duringextrusion, and structures at different part of the bar were nonuniform due to differentdeformation degree. Grains at the brim of the bar were very fine and distributed along thedirection of the extrusion, while grains at the center were coarsing. Tensile strength of theextruded alloy was 300Mpa, and the elongation was about 10.62%. The extruded alloywas aged at different temperatures. Hardness of the aged alloy exhibit a tendency ofgoing up at first, and then descending. Aged alloy could achieve a peak hardness of135HV after 225℃/14h treated. This alloy could achieve a peak tensile strength of446.67Mpa when aged at 200℃for 100h.In the end, hardening mechanism of the alloy was investigated using analysis &testing technology like TEM. A good deal of nano scale rare-earth phase precipitated intragranularly, and have good coherence with the matrix, which maked thealloy elevated mechanical properties. Nano scale particles grown up into stable stateβphase and become incoherent with the matrix with the ageing time prolonged to 70h,which deteriorated the mechanical properties of the alloy. Netlike nano scale metastablestateβ′phase formed when ageing at 200℃for 100h , which maked the alloy exhibitultimate strength. The precipitated phase could effectively block the movement of thesubgrain boundary and dislocations. The precipitation led to distortion of the crystallattices and strengthened the alloy. The well-distributed particles may have particlestrengthening effect to the alloy. Accordingly, this alloy had great ageing hardeningeffect due to Gd element. The alloy possessed excellent mechanical properties by theaction of strain strengthening ageing strengthening and solid solution strengthening.