Effects of Intermetallic Microstructure on Degradation of Mg-5Nd Alloy

Abstract

The influence of intermetallic microstructure on the degradation of Mg-5Nd alloy with different heat treatments was investigated via immersion testing in DMEM + 10 pct FBS under cell culture conditions and subsequent microstructural characterizations. It was found that T4 heat-treated sample had the poorest corrosion resistance due to the lack of finely dispersed precipitates inside grains, continuous lamellar particles along grain boundaries and outer Ca-P layer, and to the formation of a loose corrosion product layer. In contrast, the aged samples exhibited a better corrosion resistance due to their presence and to the formation of a compact corrosion layer. Their degradation behavior largely depended on the intermetallic microstructure. Corrosion was initiated in the matrix around stable globular particles Mg41Nd5 at grain boundaries. In the sample aged at high temperature 245 °C, the coexistence of lamellar Mg41Nd5 particles and their nearby Nd-poor regions enhanced the corrosion. The corrosion first started in such regions. It was shown that those finely dispersed precipitates formed during aging had no influence on the corrosion initiation. However, they indeed affected the subsequent corrosion propagation with the immersion proceeding. They supplied barriers for corrosion propagation and hence were beneficial for improving the corrosion resistance. The continuously distributed lamellar Mg41Nd5 precipitates formed at grain boundaries during aging at 245 °C supplied an additional effective obstacle to corrosion propagation. This was especially beneficial for hindering the corrosion propagation at the later stage of corrosion.

An Enhanced Understanding of the Powder Bed Fusion–Laser Beam Processing of Mg-Y3.9wt%-Nd3wt%-Zr0.5wt% (WE43) Alloy through Thermodynamic Modeling and Experimental Characterization

“…Mg alloys generally have poor corrosion resistance due to the low electrochemical stability of the Mg matrix, the strong cathodic activity of the secondary phases present, refs. [10][11][12], and the limited stability of the MgO surface film in aqueous solutions [13][14][15]. The solid solution of yttrium (Y) decreases the electrochemical activity of the Mg matrix and stabilizes the surface through the formation of Y 2 O 3 [16][17][18].…”

Experimental and Simulation Investigation of Nd Additions on As-Cast Microstructure and Precipitate Development in Mg–Nd System Alloys

“…The β -Mg 12 Nd is a metastable phase, and its amount increases with the Nd levels, based on the statistical results mentioned above. Other reports [ 18 , 44 , 45 ], however, indicated that the β e -Mg 41 Nd 5 phase could also be detected in the as-extruded Mg–Nd alloys and at high temperatures. Actually, the sequence and type of precipitation are affected by the alloy state, solidification condition, heat treatment process, etc.…”

A biodegradable 3D woven magnesium-based scaffold for orthopedic implants

“…Extensive efforts have been devoted to improving the corrosion resistance of Mg through microstructural and surface modifications [42]. The microstructural approach starts with fabricating high purity Mg or alloying it with various elements such as zinc (Zn) [43,44], calcium (Ca) [45], manganese (Mn) [46], lithium [47], or rare-earth elements [48][49][50]. Then the Mg is plastically deformed into desired geometries through extrusion, rolling, forging, or drawing.…”