The Application Of Cluster-plus-glue-atom Model In The Compositon Design Of Mg-Gd-Y-Zr And Mg-Al-Ce Alloys

Mg-Gd-Y-Zr alloys with high strength levels fall within narrow composition ranges and the content of Al as well as Ce/Al atomic ratio plays a vital role in what influence the mechanical propertites and heat resistence of Mg-Al-Ce alloys.Alloys with optimium propertites fall within special composition ranges which origin from special atom structure unit.And the special atom structure unit can be described by the cluster-plus-glue-atom model which has been established by our prvious work.The present thesis optimizes the compositon of Mg-Gd-Y-Zr and Mg-Al-Ce alloys based on the cluster-plus-glue-atom model and researchs the microstructure and mechanical propertites of the two series allos.The main contents include the following two aspects:?1?The compositon optimizion of Mg-Gd-Y-Zr alloys.The present thesis explains their composition rule by establishing the cluster-plus-glue-atom unit of Gd-containing Mg solid solution with aid of Mg matrix and Mg₅Gd precipitate phase.First,based on the structural homologue between Gd-containing Mg solid solution and Mg₅Gd precipitate phase and in combination with our previously established method for calculating the glue atoms,[Gd-Mg₁₂]Mg₅ is obtained as the chemical unit of Gd-containing Mg solid solution.Then,seven compositions are designed using different combinations of this unit and that of pure Mg[Mg-Mg₁₂]Mg₃.After a systematic experimental investigation on the microstructure and mechanical property evolutions as a function of the unit proportions,it is revealed that the Mg-10.1Gd-3.3Y-0.9Zr alloy,being issued from equi-proportion mixing of the two units,shows the strongest tendency of precipitation and reaches the highest strength of 374 MPa after aging.The composition and strength of this alloy are quite close to GW103K which is well recognized for its general mechanical performance in Mg-Gd-Y-Zr system.?2?The compositon optimizion of Mg-Al-Ce alloys.In this thesis,Mg-6.48Al-2.76Ce,Mg-6.36Al-2.18Ce and Mg-6.6Al-1.64Ce alloys are designed,where the content of Al is determined through the previously established Mg-Al binary system solid solution model and the content of Ce is adjusted slightly to make the Ce/Al value float around 1/15.After systematical study on the microstructure and mechanical properties of the three alloys under different heat treatment conditions.It is revealed that the as-cast structure of Mg-Al-Ce alloy includes Mg₁₇Al₁₂,Al₁₁Ce₃ and some Al_xCe_y compounds with uncertain composition.Al₁₁Ce₃remains stable after solution treatment at 420?,450?and 500?,but Mg₁₇Al₁₂ is dissolved after solutionization at 420?.After solid solution treatment at 550?,the needle-shaped Al₁₁Ce₃ decomposes into bulk Al-Ce compounds with higher Ce content and the Al generated by the decomposition together with the matrix Mg form Mg₁₇Al₁₂,which is enriched at the grain boundaries.Among the three alloys,the Mg-6.36Al-2.18Ce alloy with Al/Ce 15/1 has the highest tensile strength of 237 MPa and the largest elongation of 11.7%in the as-cast state,which is higher than Mg-5Al-?0.5,1,1.5,2,3?Ce-0.3Mn series alloyprepared by metal mold casting and reach the strength level of Mg-4Al?1,2,4,6?Ce-0.3Mn series alloys prepared by HPDC.