| Magnesium alloys have attracted wide attention as biomaterials.In this study,the purification of alloy processing is taken into consideration,and the high purity Mg-Zn binary alloy is prepared by gas-phase alloying with Zn which has less harm to human body,low manufacturing cost and good biocompatibility.The subsequent heat treatments and hot pressing processes were carried out to study the effects on the microstructure and properties of Mg-Zn binary alloy.The main research contents are as followed:(1)The microstructure of Mg-Zn binary alloys by gas-phase alloying is composed of elliptical a-Mg and polygonal eutectic mixtures,which are composed of MgZn and Mg7Zn3 phases,and show two typical morphologies:lamellar and rods-like.After T4 treatment,Mg7Zn3 and MgZn2 decompose extensively,while the amount of MgZn phase increased and the size of stuctures and phases of the alloy increased too.After T6 treatment,dendritic structure was formed in Mg-Zn binary alloy,with a large number ofa-Mg and Mg7Zn3,and the phase size decreases and the structure distribution is more uniform.With the increase of T4 temperature and time,the hardness of Mg-Zn binary alloy increased,and the strengthening mechanism is solution strengthening.After T6 treatment,the aging strengthening mechanism dominated and the hardness increased due to the homogeneous distribution of aged structure.(2)The corrosion potential of Mg-Zn alloy increases from-1468.8mV at condensate state to-1267.1 mV and the corrosion current density decreases to 134.47?A·cm2 24 hours after solution at 340?.After T6 treatment,the self-corrosion potential decreases to-1535.4mV and the corrosion current density increases to 685.00?A·cm2.Rct values continue to increase,from 128.70?·cm2 in the condensate state to 216.31?·cm2 at T4 state,and after T6 treatment it significantly decreased to only 26.55?·cm2.That is to say,solution treatment improves the corrosion resistance of Mg-Zn alloy in Ringer's solution,while the corrosion resistance decreases significantly after aging treatment.(3)With the increase of hot pressing time and temperature,the structure distribution becomes more uniform and the eutectic structure fines,and the content of eutectic mixture decreases.When hot pressing for 8 hours at 420?,the alloy structure has completely become flat,accompanied by precipitation and dispersion of the second phase.When the hot pressing makes the structure size finer and the second phase disperses,the strengthening mechanism is the synergistic effect of fine grain strengthening and aging strengthening.(4)The corrosion current density of the alloy increased from 56.19[iA cm2 to 175.56?A·cm2,and the charge transfer resistance decreased from 295.1?·cm2 to 30.25?·cm2 with the increase of time from 4h to 12h at 320?,10 MPa.The corrosion current density decreased from 90.51?A·cm2 to 30.05?A·cm2 and the charge transfer resistance increases from 38.39?·cm2to 515.13?· cm2 as the hot pressing temperature rised from 300? to 360?at 10 MPa for 40 min.(5)The corrosion morphology of condensed Mg-Zn binary alloys is mainly local corrosion.After T4 treatment,the corrosion morphology changed to a certain degree of overall corrosion,while after T6 treatment,the pitting corrosion density is higher,and the corrosion products distribute along a specific direction after hot pressing.After different treatments,the weight loss rate of the alloy increased but the corrosion rate decreased.With the corrosion proceeding,the pH value of the solution increased in the early stage and tended to stabilize at 10.5 Solution treatment and hot pressing can change the passive film on the surface of the alloy and protect the alloy. |
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