Research On Microstructure And Mechanical Properties Of High-performance Mg-Al-Ca Based Wrought Magnesium Alloys

As the lightest metal structural material,magnesium alloy exhibits great potential to be used in aerospace,3C,vehicle and other fields.In the past decades,great progress has been made in the mechanical properties of wrought magnesium alloys,but at present the cost of high-strength Mg-Rare-Earth(RE)alloys is relatively high,and practical applications are limited.Therefore,how to develop Mg-RE free alloys with excellent mechanical properties has become a prerequisite for its large-scale industrial application.This article is based on the compositional design and processing optimization of MgAl-Ca-based wrought magnesium alloys in order to develop high-performance,low-cost wrought magnesium alloys.The microstructure of the alloys were analyzed by means of OM,SEM,EBSD and TEM,in order to explain the mechanism of high strength and toughness.The following results have been obtained:The Mg-1.3Al-1.2Ca-0.5Zn-0.6Mn(wt.%)alloy with high strength and plasticity was prepared.The yield strength(YS)and the ultimate tensile strength(UTS)of present alloy are?411 MPa and?418 MPa respectively.Simultaneously,the Mg alloy has high plasticity and the elongation(EL)is?8.9%.The microstructure analysis shows that the high strength of the alloy is mainly attributed to the grain finement strengthening caused by the ultra-fine dynamically recrystallized(DRXed)grains.the high density dislocations in the un-DRXed region,and the precipitation strengthening and dispersion strengthening contributed by the nano-scale second phase particles distributed in the alloy matrix and grain boundary.At the same time,the DRX degree of the alloy is high,and the fine DRXed grains can accommodate the plastic strain and facilitate the plasticity.By adjusting the composition and processing parameters,the Mg-1 Al-1Ca-0.3Zn0.4Mn(wt.%)alloy with ultra-high strength was further prepared.The YS and UTS of the alloy are?435 MPa and?449 MPa respectively.While the ultra-high strength has been achieved,the good plasticity is obtained,and the EL is kept at?4.2%.The further improvement of the strength of the alloy is mainly due to the dispersion of nano acicular Al2Ca phase.After annealing,the number density of Al2Ca nano-phase is further increased,which ensures that the as-annealed alloy also maintains super high strength(?444 MPa).Finally,the Mg-Al-Ca alloy with high alloy content was developed,and the excellent mechanical properties at high temperature were obtained by combining the microalloys of Zn and Mn elements.Among them,the YS of Mg-4Al-6ca-1Zn-0.5Mn(wt.%)alloy reaches?267 MPa at 200?,and the UTS reaches-298 MPa.The high heat resistance of the alloy can be attributed to the stress field pinning dislocation movement caused by the solid solution Zn and Ca elements in the magnesium alloy matrix,the nano-sized spherical Al2Ca phase with excellent thermal stability is dispersed in the alloy matrix,grain boundary and DRXed grain,which is strengthened by Orowan mechanism.Moreover,the micro-sized Al2Ca phase is well combined with the matrix and can withstand more deformation,and the Zn and Ca elements,which are segregated in grain boundary and low angle grain boundary(LAGB),can restrict the migration of DRXed grain boundary,thus ensuring high heat resistance.