Research On Strengthening And Toughening Mechanism Of Newly Developed Low-cost Mg-Ca-Al-Zn-Mn Wrought Magnesium Alloy

Magnesium alloys,with low density and high specific strength,have wide potential application in various fields,such as transportation,aerospace and electronics.However,mechanical properties of the traditional Mg alloys are poor,and the high-strength Mg-Rare-Earth alloys are costly and cannot be used for large-scale industrial usage.How to produce high-strength and ductile wrought Mg alloys with low cost is a bottleneck problem at present.In this work,based on the compositional design and extrusion processing optimization of Mg-Ca based alloys,the following main results have been obtained:(1)The dilute Mg-1 wt.%Ca binary alloys can exhibit extremely high strength after extrusion,and the ultimate strength of X1-380 alloy is?449 MPa,and the elongation is?4.1%.The microstructure analysis showed that Ca element can effectively induce high density dislocations and produce significant grain refinement.High-density dislocations,strong fiber texture,subgrain lamellae,fine dynamic recrystallized grains,and dispersed Mg2Ca nanophases are all beneficial to the improvement of strength.In addition,the dispersed Mg2Ca nanophase can hinder the recovery of dislocations,and effectively pin the grain boundary migrations,inhibiting the growth of recrystallized grains,which leads to the alloy has high thermal stability.(2)A low amount of Mn and Al were added to the Mg-Ca based alloy to develop the Mg-Ca-Mn(XM10)and Mg-Ca-Al(XAll)alloys,which have high strength(ultimate strength>400 MPa).The microstructure analysis shows that both Mn and Al can promote the occurrence of dynamic recrystallization,weaken the deformation texture and reduce the dislocation density,so the strength of the alloy decreases.For XM10 alloy,the dispersed Mg2Ca phase and nano-Mn particles can significantly hinder the growth of dynamic recrystallized grains,thus obtaining ultra-fine grain structure;In addition,they can effectively suppress the static recrystallization and render the XM10 alloy to have an extremely high thermal stability.(3)Based on the multi-alloying strategy,a high-strength Mg-1.0Ca-1.0Al-0.3Zn-0.1Mn(wt.%)alloy was developed by adding a small amount of Ca,Al,Zn and Mn elements,among which the XAZM1100-300 alloy exhibits an excellently comprehensive mechanical properties,with ultimate strength of is 444 MPa and the elongation is 10.7%,simultaneously.The micro structure analysis shows that the mechanical properties of the alloy are related to the degree of dynamic recrystallization.Due to the addition of elements such as Ca and Al,the present alloy is prone to emit the non-basal dislocations,intrinsically.However,when the extrusion temperature is low,the residual dislocation density becomes high,and the newly generated mobile dislocations are easily dissociated into the immobile type,due to the obstacles of residual dislocations,which results in the accumulation of immobile dislocations,and sharply deteriorates the plasticity.On the one hand,when the extrusion temperature is high,the residual dislocation density becomes low,and a high-density subgrain lamellae is formed,which is favorable for the movement and multiplications of the mobile dislocation,which effectively ensures the high plasticity of the alloy.