Research On Microstructure And Mechanical Properties Of Lamellar Heterostructured Mg-Al-Sn-Ca Magnesium Alloy Sheets

In the strategic development context of carbon peak and carbon neutralization,magnesium alloys with low alloy content have been expected to achieve large-scale applications in the field of lightweight manufacturing due to their unique physical and chemical properties.However,implementing how to improve the strength and plasticity of the metal materials simultaneously to enable them to better adapt to the different complex environments that the actual production needs has become the only way for magnesium alloys to move forward.At present,researchers have developed a variety of magnesium alloy systems with good comprehensive mechanical properties such as Mg-Al,Mg-Zn and Mg-Mn through alloying methods.In addition to the optimization of composition,heterogeneous metal materials that can be prepared controllably from the perspective of structural design have also shown great research prospects in recent years.Heterogeneous materials often make use of the performance differences of heterogeneous materials to improve the performance of materials by composite means.Compared with steel,aluminum alloy,titanium alloy and other metals with excellent deformation ability,magnesium alloy with poor room temperature forming ability does not occupy an advantage in the development of heterogeneous materials.In addition,conventional heterogeneous metal materials are usually difficult to separate and recycle after use,resulting in a significant increase in the cost of use.Therefore,it is still a great challenge to develop a composite sheet with lamellar heterogeneity and good comprehensive mechanical properties based on magnesium alloy simultaneously.In response to the above problems,this paper takes Mg-3.0Al-0.5Sn（AT31,wt.%）alloy as the research object,realizes the grain refinement of magnesium alloy by Ca alloying,improves the second phase precipitation of AT series magnesium alloy,and develops a Mg-3.0Al-0.5Sn-0.5Ca（ATX3105,wt.%）magnesium alloy with high comprehensive mechanical properties.Using AT31 and ATX3105 magnesium alloys as raw materials,sandwich structure and coarse-fine grain alternating lamellar structure composite sheets were prepared by two processes of hard-plate rolling and accumulative roll bonding.In this paper,the influence of composition screening,macro structure design and optimization of processing parameters on the microstructure and mechanical properties of lamellar isomeric magnesium alloy composite sheets is analyzed,which provides a new solution for improving the strength and plasticity of magnesium alloy.The main conclusions of this paper are as follows:（1）In Mg-3.0Al-0.5Sn-x Ca（x=0.00,0.25,0.50,0.75 wt.%）alloys,with the increase of Ca content,the strength and plasticity of the alloys increase first and then decrease.Among them,Mg-3.0Al-0.5Sn-0.5Ca（wt.%）magnesium alloy exhibits the best comprehensive mechanical properties at room temperature.The yield strength（YS）,tensile strength（UTS）and elongation at break（EL）are～202.8 MPa,～267.8MPa and～22.8%,respectively.The improvement of strength mainly comes from the increase of grain boundary strengthening and precipitation strengthening effect,while the improvement of plasticity is related to the texture weaking of magnesium alloy promoting the opening of non-substrate slip systems.（2）In the process of hard-plate rolling（HPR）,the strength of the sheet is positively correlated with the thickness ratio of ATX3105 alloy layer to AT31 alloy layer,while the plasticity of the sheet is negatively correlated with it.In the process of variable temperature rolling,the strength of the sheet decreases with the increase of rolling temperature,while the plasticity of the sheet increases with the increase of rolling temperature.The rolled HPR₄（ATX3105 and AT31 alloy layer thickness ratio2.5:1）sheet at 300°C showed the best comprehensive mechanical properties,and its YS,UTS and EL were～258.6 MPa,～322.9 MPa and～9.8%,respectively.The ATX3105 alloy layer in the composite sheet has a certain annealing lag compared with the AT31 alloy layer,so the grain size difference between the layers can be better maintained at the annealing temperature of 275℃.After annealing for 10 min,the HPR₄sheet obtains the best mechanical properties,and its YS,UTS and EL are～210.8 MPa,～279.2 MPa and～16.9%,respectively.（3）In the process of accumulative roll bonding（ARB）,the strength of the alloy increases monotonously with the increase of rolling passes.The ARB₅sheet（5-pass cycle rolling sheet）has the highest YS（～205.4 MPa）and UTS（～274.9 MPa）.The plasticity of the composite sheet decreases first and then increases with the increase of rolling passes,and the ARB₄sheet（4-pass cycle rolling sheet）shows the highest EL（～17.4%）.On the one hand,the strength improvement of ARB sheet comes from the increase of fine grain layer strength caused by grain refinement,on the other hand,it is related to the structural strengthening caused by the increase of coarse and fine grain alternating layers inside the sheet.