Study On The Forming Technology,Microstructure And Properties Of Porous Magnesium Alloys Produced By Laser Additive Manufacturing

Magnesium alloys have become one of the most promising biomedical materials due to their excellent biocompatibility,mechanical compatibility and biodegradable properties.Human bone is porous,and as a bone tissue engineering material,porous magnesium alloys have good research and application prospects.At present,the manufacturing methods of porous magnesium alloys mainly include investing casting,powder metallurgy and melt direct foaming,etc.As a new type of rapid prototyping technology,laser additive manufacturing?LAM?can directly form personalized high-performance complex components.The existing researches about magnesium alloys produced by LAM mainly focus on dense magnesium alloys,and there are no systematic research reports about porous magnesium alloys produced by LAM.Therefore,it's very necessary to further systematically study the forming technology,microstructure and properties of porous magnesium alloys produced by LAM and lay the foundation for its future application in the medical field.In this paper,LAM technology was used to fabricate porous Mg-Ca alloys and porous Mg-Zn-Zr alloys.About Mg-Ca alloy,the effect of laser processing parameters on surface morphology,porosity,microstructure and mechanical properties were systematically studied.The results indicate that the porosity and surface morphology of the LAMed Mg-Ca alloys depend on the laser energy input,and the porosity of the samples ranges from 6.68%to37.26%.The LAMed porous Mg-Ca alloy shows overlapped cladding lines and periodic morphological features.With the father away from the molten pool,the grains show a transition from equiaxed crystal to columnar crystal and the grains size increases.Relative to as-cast Mg-Ca alloy,the grains of the LAMed porous Mg-Ca alloy are significantly refined and all the LAMed samples only consist of?-Mg phase and a lesser degree of MgO phase.The microhardness of LAMed samples is between 60 HV and 68 HV and the microhardness is superior to that of as-cast pure magnesium,which is mainly attributed to the grain refinement and solid solution strengthening.The ultimate compressive strength?UCS?is between 5.18 Mpa and 111.19 Mpa and the elastic modulus is between 0.518 Gpa and 1.264 Gpa.With the increase of laser energy input,the porosity decreases and the compression performance enhances meanwhile.With respect to Mg-Zn-Zr alloy,the processing parameters of the LAMed porous ZK61 alloy were firstly studied.Then the effect of Zn content on microstructure,mechanical properties and electrochemical corrosion resistance of the LAMed porous Mg-Zn-Zr alloys were systematically investigated.The results indicate that the porosity and surface morphology of the LAMed porous ZK61 alloys depend on the laser energy input as well.The porosity of porous ZK61 alloy is between 21.90%and 44.85%,and the porous ZK61 samples with higher forming quality can be obtained when energy density ranges from 1019J/mm³ to 1146 J/mm³.The LAMed porous Mg-Zn-Zr alloys with different Zn content were produced?Mg-5.2%Zn-0.3%Zr,Mg-15%Zn-0.3%Zr,Mg-30%Zn-0.3%Zr?at the energy density of 1146J/mm³.With the increasing Zn content,the surface quality of porous Mg-Zn-Zr alloy decreases,the grains are refined obviously and the precipitated phases experiences successive transitions:MgZn?MgZn+Mg₇Zn₃?Mg₇Zn₃.At the same time,the microhardness improves significantly,which ranges from 57.67 HV to 109.36 HV.The increase of microhardness mainly ascribes to fine grain strengthening,solid solution strengthening and precipitation strengthening.The compression performance of the sample first increases and then decreases with the increase of Zn content?When the Zn content is15 wt.%,the compression performance is best?.The corrosion resistance of porous Mg-Zn-Zr alloy is significantly worse than that of as-cast pure Mg and the corrosion resistance decreases as Zn content increases.