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abstract

The effects of annealing treatment on the microstructure and in vitro degradation performance of high-pressure torsional deformation (HPT) ZXJ310 alloy were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), corrosion weight loss experiments, and electrochemical workstations. The results show that when the high-pressure twisted state ZXJ310 magnesium alloy is annealed at 150 ℃, the average grain size of the alloy increases from 98.3nm in the high-pressure twisted state to 169.8217.6220.2 and 259.5nm, respectively, with the prolongation of annealing time (0-4 hours). Through TEM observation, it can be seen that the dislocation density in ZXJ310 magnesium alloy is significantly reduced; Electrochemical testing shows that as the annealing time prolongs, the corrosion potential significantly increases, and the capacitance arc radius in the Nyquist spectrum of ZXJ310 magnesium alloy gradually increases. After annealing for 4 hours, the electrochemical corrosion rate of the high-pressure twisted ZXJ310 magnesium alloy can be reduced to 0.32mm · y-1; The immersion weight loss test results of ZXJ310 magnesium alloy in simulated body fluid also showed the same trend, and the corrosion resistance of ZXJ310 magnesium alloy significantly improved after 3-4 hours of annealing; The analysis of corrosion products of ZXJ310 magnesium alloy shows that annealing treatment significantly improves the immersion corrosion behavior of the alloy in simulated body fluid (SBF) solution, increases the density and stability of the corrosion product film layer, but does not affect the type of corrosion products of the alloy. There is no difference in the types of corrosion products produced by ZXJ310 magnesium alloy under the same soaking conditions under different states. After soaking for 120 hours, Ca-P compounds containing hydroxyapatite can be produced.

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Fig.1　Microscopic morphology（a~e） and grain size statistic（f） of ZXJ310 magnesium alloys in different annealing treatmentstates（a）HPT；（b）150 ℃-1 h；（c）150 ℃-2 h；（d）150 ℃-3 h；（e）150 ℃-4 h；（f）Grain size statistic

Fig.2 Tafel curves of ZXJ310 magnesium alloys in different annealing treatment states

Fig.3 EIS spectra（a）and equivalent-circuit models（ b，c）of ZXJ310 magnesium alloys in different annealing treatment states

Fig.4 Changes of weight loss rate during immersion of ZXJ310 magnesium alloys treated at 150 ℃ for different times

Fig.5 SEM images of corrosion morphology（a~c）and morphology after removing corrosion products（d~f）of HPT state ZXJ310 magnesium alloys after immersion in SBF for different times（a，d）24 h；（ b，e）72 h；（ c，f）120h

Fig.6 SEM images of corrosion morphology（a~c）and morphology after removing corrosion products（d~f）of HPT state ZXJ310 magnesium alloy after annealing for 4 h at 150 ℃ after immersion in SBF for different times（a，d）24 h；（ b，e）72 h；（c，f）120 h

Fig.7 Immersion weight loss（a）and pH change （b）of HPT state ZXJ310 magnesium alloys and ZXJ310 magne⁃ sium alloys annealed at 150 ℃ for 4 h

Full text summary
As the annealing time prolongs, the average grain size of ZXJ310 magnesium alloy increases from 98.3nm to 259.5nm, the dislocation density gradually decreases, and the resistance of charge transfer at the interface between the alloy and SBF also increases. The electrochemical corrosion rate of the alloy significantly decreases, from the initial HPT state of 4.28mm · y-1 to 0.32mm · y-1 after annealing at 150 ℃ for 4 hours.
Compared to the HPT state ZXJ310 magnesium alloy, the electrochemical corrosion model of the alloy changed after annealing at 150 ℃ for different times. After annealing, the dislocation density of the alloy decreased, and the stability of the corrosion product film layer of the alloy was significantly improved.
3. Annealing treatment has little effect on the types of corrosion products in the alloy. Ca-P compounds can be observed in the corrosion products of ZXJ310 magnesium alloy under different annealing regimes. With the prolongation of corrosion time, the proportion of Ca-P compounds in the alloy corrosion products gradually increases. Under the action of Ca2+, HPO42-, and PO43- in OH and SBF, Ca-P compounds gradually deposit on the surface of the alloy in the form of hydroxyapatite.