Research On Microstructure And Mechanical Properities Of Low Alloying High Strength Mg-Al-Ca-Mn Wrought Magnesium Alloys

With the rapid development of the world economy,the consumption of fossil energy is becoming more and more intensified.As a result,the problems of energy depletion and environmental pollution have threatened the survival of human beings.Therefore,it is urgent to develop green energy and reduce energy consumption.Material lightening is the most effective way to save energy and reduce consumption.The development of lightweight,high-strength magnesium alloy will play an important role in solving energy pollution and realize the “Made in China 2025” green development.In order to overcome the high cost of high strength rare earth magnesium alloys and the low strength of non-rare earth magnesium alloys,this paper have designed a series of low alloying Mg-Al-Ca-Mn alloy by adjusting the ratio of Ca/Al,Ca+Al total alloying content with permanent mold direct-chill casting and traditional extrusion process,under the premise of Ca+Al total content below 2.0wt.%.Effects of the ratio of Ca/Al,Ca+Al total alloying content,extrusion temperature and aging process on the microstructure and mechanical properties of the alloy have been systematically researched.The study shows that with the increasing of Ca/Al ratio,the type of the second phase in the as-cast alloy keeps same,the size grows significantly,the number increases,which can effectively prevent grains' growth;Therefore,in the AXM050504(the ratio of Ca/Al is 1.0)alloy,the grain structure is the finest;and after hot extrusion,the as-extruded alloy has the excellent mechanical properties with the finest recrystallized grain size and the strongest matix texture.Under the premise of Ca/Al keeps 1.0,with the increasing of the total content of Ca+Al,the type of second phase is unchanged,and the number of second phase is significantly increasing,which can effectively hinder grain growing.Therefore,AXM1104(Ca+Al content is 2.0wt.%)has the smallest grain size,after hot extrusion deformation,the grains are further refined,the un-DRXed area is largest,the texture is strongest,in addition both of the high density of dislocations,LAGBs,and nano-precipitates have resulted the best mechanical properties with the yield strength of 355 MPa and the strain of 6.5%.As the extrusion temperature decreasing,the number of fractured second phases increases significantly,the size increases,DRXed grain refines,the proportion of un-DRXed area increases,the matrix texture increases significantly,and the yield strength of the alloy increases,obtaining super-high strength but poor plasticity.For as-extruded alloys,T5 has no aging strengthening effect and T6 aging strengthening effect is remarkable,and with the Ca/Al ratio decresing,the higher of the Al content,the precipitation strengthening effect incresing,and the machanical proporities is significantly improving.