Research Of AM60Magnesium Alloy Strengthened By Quasicrystals

Since the first discovery of an icosahedral quasicrystal (QC) structure in Al-Mn systemin1984, icosahedral Qc phases came into the picture quickly, and were discovered in manyalloy systems. QCs are ordered structures which may possess classically forbidden rotationalsymmetries. Due to the characteristic aperiodicity of QCs, these materials Strengthened byQCs are expected to exhibit characteristic properties. Compared with some other materials,these materials strengthened by QC structure can be exploited for industrial applications.Mg-based QCs seem to be a good candidate for applications on spacecraft andautomobile, and play importance roles in the vehicles. The utilization of magnesium in theindustry of automobile has therefore significantly increased in past few year. However, only afew magnesium alloys especially produced by pressure die-casting are used since many ofthese materials have lower mechanical properties than that of aluminum alloys.AM60alloy system is comprehensively used in industrial circle. Compared with AZ91magnesium alloy, the ductility of that is better, but the strength of AM60is lower. However,little the properties of AM60have been studied. Many studies focus on the microstructure andmechanical properties of AM60alloy with the addition of QCs master alloy. If people wan tomake its properties satisfy the automobile wheel hubs, they must take action to improve theproperties of AM60. Therefore, this study is to make good use of the various properties ofQCs and improve the properties of AM60. In this paper, there are three parts which are shownas follows.The first Part, fabricate a kind of Mg-Zn-Y ternary alloy containing quasicrystalsintermediate alloy have been fabricated under gravity casting conditions by designingchemical compositions and optimizing processing parameter, using SEM, XRD and EDSanalysis testing methods to study the alloy composition and technological parameter impacton the morphology, distribution, quantity, quasicrystal phase composition of MZYquasicrystal phase and quasicrystal phase thermodynamic stability. Choosing quasicrystalmaster alloy containing a high volume fraction of quasicrystals as reinforcement add intoAM60alloys and study the quantity of MZY quasicrystal master alloy impact on microstructure, properties of AM60.A small amount of Y changes the primary phase from the α-Mg+MgxZnyto thequasicrystals phase. The composition of the primary I-phase is about Mg42Zn50Y8whichpresents the shape of four, five or six smooth petals. An eutectic microstructure involving theMg7Zn3phase and I-phase is developed in the Mg-Zn-Y ternary system, the primary flakycrystal of Mg7Zn3or the I-phase imply the existence of the (I-phase+Mg7Zn3) two-phase fieldin Mg-Zn-Y system.The definite addition of Mg42Zn50Y8QCs master alloy into AM60alloy can change theformation and growth processes of the grain during solidification, the grain size of alloysdecreases and the volume fraction of grain boundary phases increases with adding a certainamount of Mg42Zn50Y8QCs master alloy. The macro-hardness of AM60increase from54HBto74.5HB, and the ultimate tensile strength (σb) and yield strength(σ0.2) for Qc-dispersedalloys are in the range of165-204MPa and75-100MPa at room temperature respectively, butdoes not bring about obvious change in elongation.The second Part, fabricate a kind of MZYM alloy containing quasicrystals intermediatealloy have been fabricated, and discuss the effects of MZYM quasicrystals addition on AM60.The aim of the study is also to discuss the effects of Si addition on AM60. In the end, discoverthe appropriate composition, and confirm the effects of Si and MZYM quasicrystals additionon AM60.The Mg-Zn-Y-Mn quasicrystals intermediate alloy is mainly composed of α-Mg matrixphase, the Mg40Zn46Y9M5quasicrystals phase and Mg7Zn3phase and-Mn. The primaryflaky crystal of Mg7Zn3or the Mg40Zn46Y9M5quasicrystals imply the existence of thetwo-phase field in Mg-Zn-Y-Mn system. With the increase of Mn content, organizationstructure of the Mg40Zn46Y9Mn5quasicrystals change from mushroom to garland, and thenchange into the garland with pistil.The definite addition of Mg40Zn46Y9Mn5QCs master alloy into AM60alloy can changethe formation and growth processes of the grain during solidification, the grain size of alloysdecreases and the volume fraction of grain boundary phases increases with adding a certainamount of Mg40Zn46Y9Mn5QCs master alloy and the macro-hardness of AM60increase from54HB to74HB, and the ultimate tensile strength (σb) and yield strength(σ0.2) for Qc-dispersed alloys are in the range of165-206MPa and75-117MPa at room temperaturerespectively, the elongation of AM60increase to7.9%.Adding1.0%Si (wt.%) into the AM60alloy, there is Mg2Si phase forming in the alloysystem. The shape of Mg2Si is Stick or irregular clumps. When the amount of Si surpasses1.5wt.%, the Mg2Si gathers and grows. The definite addition of Si AM60alloy can change theformation and growth processes of the grain, the grain size of alloys decreases with adding acertain amount of Si. Mg2Si improving the strength of AM60alloy.Adding8.0wt.%Mg40Zn46Y9Mn5QCs master alloy and1.0wt.%Si into the AM60magnesium alloy, the macro-hardness of AM60increase from54HB to77HB, and theultimate tensile strength (σb) and yield strength(σ0.2) for Qc-dispersed alloys are in the rangeof165-212MPa and75-119MPa at room temperature respectively, the elongation of AM60declines.The third Part, the study confirms the most appropriate composition, and discusses theeffects of Se and MZYM quasicrystals addition on AM60.Adding Se into the AM60alloy, there is Al2Se3phase forming in the alloy system. Thedefinite addition of Si AM60alloy can change the formation and growth processes of the phase, the size of phase decreases with adding a certain amount of Se and Al2Se3improvingthe elongation of AM60alloy.Adding8.0wt.%Mg40Zn46Y9Mn5QCs master alloy and0.8wt.%Se into the AM60magnesium alloy, the macro-hardness of AM60increase from54HB to73HB, and theultimate tensile strength (σb) and yield strength(σ0.2) for Qc-dispersed alloys are in the rangeof165-201MPa and75-88MPa at room temperature respectively, the elongation of AM60changes from6.5%to10.2%.