# In Vitro Corrosion Behavior of Zn3 Mg0.7Y Biodegradable Alloy in Simulated Body Fluid (SBF)
## 2 Materials and Methods  
Experimental materials were realized from pure zinc (99.995%) in an electrolyte bath and pure magnesium and master-alloy MgY(70/30 wt%) bought from HunanCo China, Hunan, China, molten for 600 s at 480 \({}^{\circ}\)C in a standard oven with induction with Argon-purged gas (\(\sim\)0.75 atm), Induct-Ro, Iasi, Romania. The samples consisted of three materials: pure Zn, Zn3 Mg and Zn3 Mg0.7Y. The materials were obtained as bars machined from ingots (approx. 110 g), which were prepared by melting from high-purity raw materials. Zn, MgY and Mg were obtained from the following material quantities: for Zn3 Mg0.7Y, we used 96.0 g pure Zn, 2.9 g MgY and 1.6 pure Mg. Zinc loss by volatilization was avoided by keeping a low melting temperature and by enhancing the element dissolution in the metal bath. The samples were re-melted five times to obtain proper chemical and structural homogeneity and to reduce the voids and microcracks from the melting process. To highlight the effect of the re-melting, we performed a non-destructive test, using fluorescent penetrant liquids, Figure 1a,b. We used the hydrophilic post-emulsification method to detect different discontinuities of the melted alloy, such as cracks or porosity. The samples were cleaned in a technical alcohol machine before testing. We used a level-four sensitivity penetrant and a hydrophilic emulsifier at 7% concentration. A non-aqueousdeveloper was used to obtain a better contrast, which amplified the indications. Standard parameters were used as follows: penetrant dwell time: 30 min; emulsifier time: 3 min; developer time: 15 min. Inspection was performed under UV light at 3000 \(\mathrm{\SIUnitSymbolMicro W}\)/cm\({}^{2}\) intensity measured at 12 inches [21]. The results of the remelting are visible primarily in the case of alloy and less of Zn pure, highlighting a reduction of surface defects. Mechanical property modification was evaluated through hardness Vickers tests (HV) using HVT-1000 equipment (test force: 2.942 N-300 gF; dwell: 10 s; objective: 40\(\times\) magnification, JVC TK-C92 1 EC for surface image of the indentation trace) and a scratch test with CETR UMT-2 Tribometer equipment (the test consisted of the application of an increasing force of 1-15 N over a distance of 10 mm with 1 mm/s rate on the samples). Friction force (F\({}_{\mathrm{x}}\)) and acoustic emission (AE) data were registered during the test time, and the scratch distance was measured and recorded at a total sampling rate of 20 kHz. The apparent coefficient of friction (COF) was calculated for each sample and plotted against distance (mm). These parameters are important to establish the mechanical property modification with the addition of Mg and Y elements to pure Zn. Electrochemical measurements were performed with a PARSTAT 4000 electrochemical system (Princeton Applied Research, Oak Ridge, TN, USA). A C145/170 type three electrode corrosion cell (Radiometer, Neuplassans, France) was used for both the dynamic measurements and the electrochemical impedance spectroscopy determinations, which is a glass cell with the possibility of liquid corrosion; static conditions were preferred in the present measurements [22]. The placement of the samples in the working cell was performed by means of a Teflon washer with an inner diameter of 7 mm, so that, for all samples, the surface of the working electrode (the portion of the sample exposed to the corrosion environment) was also equal to 0.385 cm\({}^{2}\)[23]. A flat platinum electrode (S = 0.8 cm\({}^{2}\)) was used as an auxiliary electrode, and a saturated calomel electrode as a reference. All potentials were measured in relation to this electrode, but for simplicity, this is not specified in the tables and in the text. The solution used (Simulated Body Fluid--SBF) was naturally aerated.