Evolution of microstructure and electrochemical corrosion characteristics of cold compacted magnesium

Abstract

The main advantage of magnesium and its alloys is high specific strength and biocompatibility. A modern approach to magnesium-based materials preparation is powder metallurgy. This technique allows preparation of new materials with a unique structure, chemical composition, and controlled porosity. In this study, cold compaction of magnesium powder was studied. Magnesium powder of average particle size of 30 μm was compacted applying pressures of 100 MPa, 200 MPa, 300 MPa, 400 MPa and 500 MPa at laboratory temperature. Influence of compacting pressure was studied with microstructural and electrochemical corrosion characteristics analysis. The resulting microstructure was studied in terms of light and electron microscopy. Obtained electrochemical characteristics were compared with those of wrought magnesium. Compacting pressure had a significant influence on microstructure and electrochemical characteristics of prepared bulk magnesium. With the increase in compaction pressure, the porosity decreased. Compacting pressures of 300 MPa, 400 MPa and 500 MPa led to the similar microstructure of the prepared material. Polarization resistance of compacted magnesium was much lower and samples degraded faster when compared to wrought magnesium. Also, the corrosion degradation mechanism changed due to the microstructural differences between the material states.

Electrochemical Corrosion Behavior of Pure Mg Processed by Powder Metallurgy

“…The oxide layer present on the powder particles before compaction and subsequently creating a net between the mechanically bonded powder particles was less corrosion resistant than pure Mg. The propagation of the corrosion attack documented in Figure 5b is in agreement with previous results of experiments performed in HBSS and enriched HBSS [16,36]. However, the used HBBS were more aggressive, and more pronounced corrosion degradation of the sample was observed.…”

“…While in the Cl containing solutions only MgO oxides and Mg(OH) 2 hydroxides, later transformed to MgCl 2 by aggressive Clions attack, are created, in the case of HBSS additional corrosion products create. Due to the different chemical compositions of the solution, exposure of Mg materials to HBSS provides conditions also for additional creation of phosphates and hydrogencarbonates [36].…”

“…As can be seen in Figure 5, the influence of porosity on the material corrosion properties observed here is in accord with literature: the higher the porosity the lower the corrosion resistance. The negative influence of compacted bulk porosity and layers of corrosion products present on the surfaces of compacted Mg powder particles on material properties was also discussed in [6,[14][15][16]18,36].…”

evolution of microstructure of magnesium materials prepared by SPS using various compacting pressures

“…The SEM observation of etched metallographic specimens clearly shows the highest porosity of the experimental material prepared at the lowest (20 MPa) compacting pressure (Figure 1a). It is the same level of porosity as for the original green compact [22]; therefore, 20 MPa load during the SPS does not contribute to the compaction of the green compact. With the increase of compacting pressure during SPS, the porosity in experimental materials continually decreases to an apparent minimum of 5 % (for 80 MPa).…”