Study of the Morphology and Properties of Biocompatible Ca-P Coatings on Mg Alloy

Magnesium alloys are considered as potential biomaterials for use in orthopedic implantology. The main barrier to the use of Mg alloys in medicine is their overly fast and irregular degradation in body fluids. The use of protective calcium phosphate coatings to increase the corrosion resistance of Mg alloy (AM50 alloy: 4 wt.% Al, 0.3 wt.% Mn, 0.2 wt.% Zn, rest Mg) was examined in this study. The scientific goal of the study was the assessment of the influence of calcium phosphate layer morphology on the corrosion process in Ringer’s solution. Modification of the coating morphology was obtained by changing the chemical composition of the phosphatizing bath using NaOH (NaAM50 sample) or ZnSO4 (ZnAM50 sample). In practice, a more dense and uniform coating could be obtained by the immersion of AM50 alloy in a solution containing ZnSO4 (ZnAM50 sample). In this study, an adhesion test performed on the ZnAM50 sample indicated that the critical load was 1.35 N. XRD phase analysis confirmed that the obtained coatings included dicalcium phosphate dihydrate (CaHPO4*2H2O). The coatings prepared on the NaAM50 and ZnAM50 samples are effective barriers against the progress of corrosion deeper into the substrate. After 120 h immersion in Ringer’s solution, the volume of the evolved hydrogen was 5.6 mL/cm2 for the NaAM50 and 3.4 mL/cm2 for the ZnAM50 sample.

Effect of Boron on the Grain Refinement and Mechanical Properties of as-Cast Mg Alloy AM50

The effect of B addition on the microstructure and mechanical properties of AM50 was investigated, and the mechanism of grain refinement was clarified. Optical microscopy, X-ray diffraction, scanning electron microscopy, and electron probe microanalysis were used to characterize the microstructure evolution. The grain size of as-cast AM50 decreased from 550 μm to 100 μm with the B content increasing from 0 to 0.15 wt.%. AlB2 particles in the Al-3B master alloy transformed to Mg-B, and acted as the grain refiner. The addition of B to as cast AM50 alloy results in improved mechanical properties of AM50 + xB alloys. For instance, the YTS (yield tensile strength), UTS (ultimate tensile strength), and elongation of as cast AM50 + 0.15 wt.% B alloy was 94 MPa, 215 MPa, and 12.3%.

Characterization of Squeeze Cast Mg Alloy AM50 Containing Ca Addition

Metallographic analyses on microstructure of squeeze cast magnesium alloy AM50 with different levels of calcium addition are performed via optical microscopy (OM), and scanning electron microscopy (SEM). The OM results show the calcium has a grain refining effect on the base alloy AM50 with the level of Ca addition up to 2 wt.%. As the Ca content further increases, its grain refining effect becomes limited. The SEM observation reveals the addition of 2 wt.% Ca to the AM50 alloy leads to the formation of a continuous network of eutectic phases along grain boundaries while the discontinuous divorced secondary eutectic β-Mg12Al17 is present in the microstructure of AM50 containing also the primary α-Mg, and Mn-Al intermetallic particles. The elemental mapping by the energy dispersive spectroscopy (EDS) indicates the presence of the major alloying elements of Al and Ca along grain boundaries in the squeeze cast AM50 alloy with Ca addition.

Predicting the Influence of Microporosity on the Mechanical Properties and Fracture Behavior of High-Pressure Die-Cast AM50 Magnesium Alloy

In this paper, experimental and finite element modeling methods were adopted to investigate the effects of microporosity on the tensile properties and fracture behavior of high-pressure die-casting (HPDC) AM50 alloy. By specimen-to-specimen fractographic analysis, the variability in tensile properties could be quantitatively correlated with the areal fraction of the porosity presented in the corresponding fracture surfaces by using a simple power law equation. Numerical models of synthetic microstructures with different pore sizes, areal fractions of pores and pore distributions were established. Based on the experimental and numerical simulation results, it could be concluded that the fracture will initially occur in the region where has the highest intensity of equivalent stress field (i.e., contains the most highly localized cluster of pores and shrinkage), and then, fracture crack will fast propagate through the adjacent regions which have the relatively high intensity of stress field.

Effect of Microporosity on the Tensile Properties of High-Pressure Die-Cast AM50 Magnesium Alloy

Cast Magnesium alloys often exhibit large variability in fracture related properties such as ductility. In this study, the characteristics of micro-voids in high-pressure die-cast (HPDC) AM50 alloy were investigated by microstructural detecting. Specimen-to-specimen fractographic analysis of tensile fractured surface was executed to summarize the relation between microporosity and tensile properties. The results indicated that the variability in tensile properties is quantitatively correlated to the areal fraction of porosity in the corresponding fracture surface, which could be expressed by a power law equation. All the results proved that the most highly localized cluster of micro-voids is most preferentially to be the origin of fracture, and then, fracture crack will preferentially propagate through the adjacent regions that with large porosity.