Preparation Of Mg-Zn-Ca Alloy Amorphous Coating By Laser Remelting Method And Its Corrosion Resistance

Degradable bio-magnesium alloys are widely used in the field of human hard tissue repair materials due to their excellent mechanical compatibility and biocompatibility.However,due to the negative chemical potential of metal magnesium,the corrosion rate is too fast,which seriously restricts the clinical application of bio-magnesium alloy.It is reported that the amorphization of magnesium alloy can effectively improve its corrosion resistance,but the amorphous method prepared by the traditional preparation method is small and cannot meet the practical application.Therefore,the Mg₆₀Zn₃₅Ca₅ alloy is the research object.Firstly,the influence of laser remelting process on the microstructure of magnesium alloy is studied.Then,the magnesium alloy amorphous coating is prepared by further optimization of process parameters.Finally,the magnesium alloy amorphous coating is evaluated.Layer corrosion resistance,degradation properties and biological activity.The main research results of this paper are as follows:（1）The effect of laser remelting process on the microstructure of Mg₆₀Zn₃₅Ca₅alloy was studied.The research shows that the as-cast magnesium alloy is mainly composed of gray matrix phase,black flake phase and white irregular dendrite phase.The master alloy has more defects and holes;the surface of magnesium alloy after laser remelting experiment forms remelting.Gradient layer,the surface layer is amorphous layer without obvious diffraction contrast,followed by snowflake structure,the bottom layer is base layer;the tissue size under different laser processes has certain difference,the power is 500 W,the sweep speed is 90 mm/s In the case of,the formed remelted layer has no diffraction contrast.（2）The preparation of amorphous gradient layer by laser remelting method and its influence on mechanical properties were studied.The results show that the amorphous content on the surface of magnesium alloy is as high as 95.8%when the laser power is 500 W and the scanning speed is 90 mm/s.It can be determined that the amorphous coating is successfully prepared on the surface of Mg₆₀Zn₃₅Ca₅ alloy after laser remelting..The microhardness of the master alloy is 188 HV.After the remelting treatment of the above laser process,the hardness of the alloy surface shows a gradient change,up to 540 HV,which is 2.8 times higher.The friction coefficient of magnesium alloy was reduced from 0.63 to 0.20,and the effect of laser power and scanning speed on the properties of the alloy showed a parabolic change pattern with an open downward.（3）The corrosion resistance and corrosion mechanism of Mg₆₀Zn₃₅Ca5 alloy in simulated body fluid before and after laser remelting were studied.The results show that self-corrosion potential after laser processing is shifted from-1.6687 to-1.3346 V,and the positive offset 0.3341 V.The self-corrosion current density decreased from0.2385 mA/cm² to 0.0199 mA/cm²,which was reduced by 0.2186 mA/cm².The degradation rate of magnesium alloy is reduced from 5.450 mm/y to 0.455 mm/y,and the slowing rate is more than one order of magnitude,which meets the requirement that the corrosion rate of magnesium alloy implant materials is less than 0.5 mm/y.