The Calculation Study On The Alloy Phase In Typical Wrought Magnesium Alloy

With the development of first-principles calculation independent of any empririalparameters, some thermophysical and mechanical properties of materials can bepredicted which are important to design new materials. The research of alloy phase isvery important for application and development of magnesium alloys, but the study ofalloy phase in magnesium alloys are not enough. There are a lot of unknown phase inthe magnesium alloy, the chemical composition and crystal structure of somecompounds need to be confirmed, the thermodynamics and kinetics studies of the alloyphase in magnesium alloys are notenough, therefore it is quite important to study thealloy phase in magnesium alloys. To accelerate the study of alloy phase in magnesiumalloys, the first principle calculation method was used to research the alloy phase intypical wrought magnesium alloys.Firstly, the structural parameters, formation enthalpy, cohesive energy, elasticconstant and the ideal strength of the alloy phase Al₄Sr, Al₂Sr, Al₉Sr₅, Mg₂Sr andMg₁₇Sr₂in AZ31magnesium alloys with Sr were calculated by the first principlecalculation. The calculated results of paramenters of the alloy phase agree well withthe experimental values. The formation enthalpy and cohesive energy of the alloyphase show that all the phase considered are stable, and the phase Al₄Sr is the stablestamong these phases. The ratio of the shear modulus and bulk modulus （G/B） indicatesthat Al₂Sr and Al₉Sr₅are both brittle, Al₄Sr and Mg₂Sr are ductile. The ideal tensilestrength of the Al₄Sr is6.53GPa, which is the largest one among these phases, and itscritical strain is10.23%which is smallest one. The ideal tensile strength of the Mg₂Sris2.97GPa, which is the smallest one among these phases, and its critical strain is22.10%which is largest one. The ideal tensile strength of the Al₂Sr, Al₉Sr₅and Mg₁₇Sr₂phase are6.26GPa,3.70GPa and5.34GPa, respectively and their critical strain are18.7%,12.0%and20%, respectively.Secondly, the experimental work was designed to verify the calculation results ofthe phase properties of alloy phase Al₄Sr, Al₂Sr, Al₉Sr₅, Mg₂Sr and Mg₁₇Sr₂. Thescanning electron microscopy （SEM）, energy dispersive spectrometer （EDS） and X-raydiffraction （XRD） were used to analysis the morphology and type of the intermetalliccompounds in the AZ31magnesium alloys adding with Sr. The mechanical propertiesof AZ31magnesium alloy with addition of Sr was detected by Micro-hardness tester. Lastly, the structural parameters, formation enthalpy, cohesive energy, elasticconstant and the ideal strength of the alloy phase AlLi, Al₂Y and Al₂La inLA141magnesium alloys with change of Y/La ratio were calculated by the firstprinciple calculation. The calculated results of paramenters of the alloy phase agreewell with the experimental values. The formation enthalpy and cohesive energy of thealloy phase show that all the phase considered are stable, and the phase Al₂Y is thestablest among these phases. The ratio of the shear modulus and bulk modulus （G/B）indicates that all the phases considered are brittle. The tensile strength of Al₂Y is11.96GPa, which is the largest among these phases, and the critical strain value is14.4%,which is the smallest one. The tensile strength of AlLi phase is10.36GPa, but itscritical strain value is up to78.9%. The calculated strength of Al2La phase is9.43GPa，which is the smallest, and its critical strain value is13.7%.