Effect Of Ca Addition On Microstructure,corrosion Properties And Mechanical Properties Of AZ61-1Nd Alloy

Magnesium and its alloys have excellent physical and chemical properties,such as low density,high specific strength and stiffness,good damping performance,good biocompatibility,and recyclability.It has received increasing attention in fields such as aviation and navigation,rail transit,electronic communication,and medical engineering,demonstrating enormous application potential.However,there are still many difficulties to overcome in order to broaden the further application of magnesium alloys in the maritime business,such as the significant disadvantages of magnesium alloys such as low strength,poor plasticity and poor corrosion resistance.At present,although the performance of AZ-series alloys can meet the basic needs of daily life,the use of the alloys is seriously affected in the face of complex corrosive environments.In this paper,the effect of Ca content on the corrosion resistance and mechanical properties of AZ61-1Nd alloy in the as-cast state is investigated based on AZ61-1Nd alloy,and the corrosion mechanism of the alloy with different Ca content is revealed;On this basis,the corrosion resistance and mechanical properties of different alloys along the extrusion direction and perpendicular to the extrusion direction after hot extrusion were further investigated.The correlation mechanism between the cross-sectional and longitudinal microstructures of the alloys in the extruded state and the corrosion performance and mechanical properties of the alloys was elucidated.The main experimental findings are as follows:（1）Firstly,the microstructure,corrosion properties and mechanical properties of the as-cast AZ61-1Nd-x Ca（x=0,0.5,1,2 wt.%）alloy were studied by comparison.The results show that the microstructure in the as-cast AZ61-1Nd alloy without the addition of Ca elements consists ofα-Mg,β-Mg₁₇Al₁₂,Al₂Nd and Al11Nd3 phases.When Ca is added to the as-cast alloy,there is Al₂Ca phase precipitated and it increases with the increase of Ca content.The microstructure of the cast alloy shows that the shape of the precipitated phase mainly consists of granular or massive when the Ca content is less than 0.5 wt.%.When the Ca element content is greater than 2 wt.%,the second phase exists in a reticular formation.In terms of corrosion resistance,the as-cast AZ61-1Nd-x Ca alloy has the following corrosion resistance from high to high:AZ61-1Nd-0.5Ca<AZ61-1Nd-2Ca<AZ61-1Nd<AZ61-1Nd-1Ca.The cast AZ61-1Nd-1Ca alloy exhibited the best corrosion resistance.In addition,as shown by the microhardness data,the addition of Ca elements increased the hardness of the as-cast AZ61-1Nd-x Ca alloy from 53.63 HV to 65.26 HV.The changes in the corrosion resistance and hardness properties of the as-cast alloy are mainly attributed to the grain refinement and the reticulation of the second phase.（2）Secondly,the microstructure,corrosion properties and mechanical properties of the cross-section of the extruded AZ61-1Nd-x Ca（x=0,0.5,1,2 wt.%）alloy were investigated by comparison.It is shown that with the addition of Ca elements,the Al₂Ca phase appears in the cross-section of the extruded alloy and is accompanied by an increase in the volume fraction of the second phase.In addition,when the Ca content is less than 1 wt.%,it has a fine grain strengthening effect,however,as Ca increases to 2 wt.%,a coarsening of grain size occurs.For the corrosion resistance of the cross section of the extruded AZ61-1Nd-x Ca alloy,it can be seen that the extruded AZ61-1Nd-1Ca alloy cross section has the best corrosion resistance.Also,comparing the variation of the hardness values of the extruded AZ61-1Nd-x Ca alloy cross-sections,it can be seen that the hardness of the four extruded alloy cross-sections monotonically increases with the increase of element Ca.The variation in the corrosion resistance and hardness of the extruded alloy cross sections is mainly due to the fine grain size and the diffuse,uniformly distributed second phase.（3）Finally,the microstructure,corrosion properties and mechanical properties of the longitudinal sections of the extruded AZ61-1Nd-x Ca（x=0,0.5,1,2 wt.%）alloy were investigated by comparison.The results show that the morphology of the second phase in the longitudinal section of the extruded AZ61-1Nd-x Ca alloy changes and is distributed in a linear pattern along the extrusion direction.Comparing the cross-section of the alloy in the extruded state,the second phase is distributed in a homogeneous and diffuse pattern.By comparing the corrosion rate and morphological changes of corrosion products in the longitudinal section of the extruded AZ61-1Nd-x Ca alloy,the longitudinal section of the extruded AZ61-1Nd-1Ca alloy exhibited the best corrosion resistance.However,the corrosion resistance of the cross section of the same extruded alloy is better than that of the longitudinal section of the extruded alloy.In addition,comparing the mechanical properties values of the longitudinal sections of the extruded AZ61-1Nd-x Ca alloy,it was found that the yield strength and ultimate tensile strength of the extruded alloy were slightly reduced by the addition of Ca elements.Among them,the elongation of the extruded alloy was significantly reduced.However,the hardness of the longitudinal section of the extruded alloy increased with the increase of Ca content.Moreover,the difference in microhardness between the cross-sectional and longitudinal sections of the same extruded alloy is not significant.It can be seen that the changes in the longitudinal mechanical properties and corrosion resistance of the extruded alloy are attributed to the grain refinement and the linearly distributed second phase organization.