Effect Of Heat Treatment Process On Microstructure And Mechanical Properties Of Mg-Gd-Y(-Zn)-Zr Alloy

Rare earth magnesium alloys has attracted much attention for its comprehensive mechanical properties of excellent,but the larger for the amount of rare earth elements to a certain extent,limits its extensive application,so low content of rare earth magnesium alloy research is of great significance.In this paper,three kinds of magnesium alloys with different compositions were prepared by metal gravity casting.The specific components were Mg-3Gd-4Y-0.5Zr,Mg-3Gd-4Y-1Zn-0.5Zr,Mg-6Gd-4Y-1Zn-0.5Zr.The three alloys were denoted as 1#,2#,3# respectively,the effect of different heat treatment processes on the microstructure and mechanical of the alloys were investigated.The results show that the as-cast structure of alloy 1# is composed of ?-Mg and Mg5(Gd,Y)phase.the as-cast structure of alloy 2# ?-Mg and 18R-LPSO structures,and occasionally a very small amount of Mg5(Gd,Y,Zn)phase is found.The as-cast microstructure of alloy 3# was composed of ?-Mg,Mg5(Gd,Y,Zn)phase and 18R-LPSO structure.The microstructures of the three alloys at different temperatures(400 ?,480?,500?,520?)for 10 h were studied.Zr element enrichment at grain boundary,provides necessary conditions for the cuboid phase formation.In the three alloys,the number of cuboid phase in the alloy 2# decreases with the increase of the solution treatment temperature,and the alloy 1# and the alloy 3# show the opposite rule.The alloy 1# and the alloy 3# are the same,But the reasons for the formation of different.When the solution temperature is 400 ?,the second phase in the three alloys can not be fully decomposed and uniformly diffused into the matrix;The 18R-LPSO structure in alloy 2# and 3# is decomposed.During the solution treatment,the 14H-LPSO structure at the grain boundary can act as a pinning effect on the grain boundary,effectively preventing the grain from growing up.According to the alloy 3# at 520? solution treatment of different time tissue changes,The decomposition process of 14H-LPSO structure can be summarized as follows: First,the 14H-LPSO structure at high temperature is dissolved and its boundary becomes rounded,and the elements are segregated from the restraint of 14H-LPSO structure.Secondly,The partial clustering of the elements causes the formation of a partial supersaturated solid solution or a square phase within the region,these small supersaturated solid solution and the cuboid phase in a straight line,with the extension of time,supersaturated solid solution and the cuboid phase becomes disordered,or even dispersing and dotted.The aging treatment temperature can advance the aging peak time and reduce the hardness value of peak aging.The higher the temperature of aging treatment,the higher the elongation rate,the decrease of tensile strength and yield strength.