Preparation, Mechanical Properties And Corrosion Properties Of MgZnCa Amorphous Alloys And Their Matrix Composites

More and more attention has been paid to the biological research on magnesiumalloy due to its low density and biodegradable property. However, magnesium alloy hassome limitation such as their strength would deteriorate gradually during thecorrosion/degradation process and the rate of corrosion/degradation of currentlyavailable magnesium alloys faster than bone healing rates. Mg-based amorphous alloysexhibit great improvement in strength property and high corrosion resistance, which areparticularly attractive for biological applications. Mg-Zn-Ca amorphous was selected asa promising material with high specific strength and good biocompatibility.However, Mg-based amorphous alloys are typically brittle at room temperature.The preparation of Mg-Zn-Ca amorphous matrix composites by using in situ or ex situmethods has been proven to be an effective way to overcome the brittleness ofamorphous alloys. In addition, it is found that even the compositions which are ineutectic point Mg-Zn-Ca alloy show different glass forming capability （GFA）. It isnoticeable that most Mg-based amorphous matrix composites are prepared under thehigh vacuum with the high pure raw materials, which increase the cost and bad for theirengineering applications. In addition, the corrosion behaviors of Mg-based amorphousmatrix composites are different from that of the fully amorphous alloys or theconventional Mg alloys due to the effect of partially crystallization. It makes sense todevelop new Mg-Zn-Ca amorphous matrix composites under the low vacuum with theraw materials, adding the biocompatibility of Y, Mn and Fe particles element and havefundamental corrosion studies on Mg-Zn-Ca amorphous matrix composites. Themicrostructures of the bulk samples were analyzed by X-ray diffraction （XRD）,scanning electron microscope （SEM） and the thermal stability of samples wasinvestigated by using a differential scanning calorimeter （DSC）.First, in this paper, Mg₆₉Zn₂₇Ca₄and Mg₆₈Zn₂₈Ca₄sample were prepared bycopper mold casting under the low vacuum, and the raw materials used in preparingthese alloys were commercially pure materials. The Mg₆₉Zn₂₇Ca₄alloy exhibits a fullyglass structure, and it has high mechanical properties and good corrosion resistance.Furthermore, the glass forming ability of Mg₆₉Zn₂₇Ca₄alloys have decreased withdecreasing the cooling rate. The α-Mg and Mg-Zn dendrites can be formed in theMg₆₉Zn₂₇Ca₄amorphous matrix with the diameter is3mm. Second, the compressive strength of the Y-doping alloys increased significantlyalthough the glass formation ability decreased slightly. Especially, the Mg₆₈Zn₂₇Ca₄Y₁alloy exhibited the highest strength above1010MPa and an excellent plastic strainabove3.1%. The Y-bearing Mg-Zn-Ca alloys displayed good bio-corrosion resistancein NaCl solution and SBF solution at37C. The present Mg-Zn-Ca-Y alloys have goodbio-corrosion properties than traditional Mg alloy and pure Mg.Third, the Mn-bearing Mg-Zn-Ca alloys although decreased the glass formationability and mechanical properties, the Mn doped Mg₆₉Zn₂₇Ca₄alloys exhibited morepositive corrosion potential values and lower corrosion current density thanMg₆₉Zn₂₇Ca₄amorphous, ZK60and pure Mg. It is notice that the corrosion surface ofMg68.5Zn27Ca4Mn0.5is temper and no obvious crack in SBF at37℃with immersion85h time, which shows good biological corrosion resistance.Finally, it was found that although the glass forming ability was reduced, thecompressive strength and strain of the Mg₆₉Zn₂₇Ca₄/Fe alloy were increased obviously.With the Fe particles addition, α-Mg and Mg-Zn dendrites can be embedded in theamorphous matrix, which can be highly responsible for the enhanced compressivestrength and fracture strain. In addition, the Mg₆₉Zn₂₇Ca₄glassy alloy andMg₆₉Zn₂₇Ca₄/Fe alloy have much better corrosion resistance in3.5wt.%NaCl solutionthan AZ31and pure Mg, which may be good candidates to be used as biomedicalmaterials.