Effect of thermal treatment on the bio-corrosion and mechanical properties of ultrafine-grained ZK60 magnesium alloy

Mg/ZrO2 Metal Matrix Nanocomposites Fabricated by Friction Stir Processing: Microstructure, Mechanical Properties, and Corrosion Behavior

Magnesium (Mg) and its alloys have attached more and more attention because of their potential as a new type of biodegradable metal materials. In this work, AZ31/ZrO₂ nanocomposites with good uniformity were prepared successfully by friction stir processing (FSP). The scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize the microstructure of the composites. The mechanical properties, electrochemical corrosion properties and biological properties were evaluated. In addition, the effect of reinforced particles (ZrO₂) on the microstructure and properties of the composite was studied comparing with FSP AZ31 Mg alloy. The results show that compared with the base metal (BM), the AZ31/ZrO₂ composite material achieves homogenization, densification, and grain refinement after FSP. The combination of dynamic recrystallization and ZrO₂ particles leads to grain refinement of Mg alloy, and the average grain size of AZ31/ZrO₂ composites is 3.2 μm. After FSP, the c-axis of grain is deflected under the compression stress of shoulder and the shear stress of pin. The ultimate tensile strength (UTS) and yield strength (YS) of BM were 283 and 137 MPa, respectively, the UTS and YS of AZ31/ZrO₂ composites were 427 and 217 MPa, respectively. The grain refinement and Orowan strengthening are the major strengthening mechanisms. Moreover, the corrosion resistance in simulated body fluid of Mg alloy is improved by grain refinement and the barrier effect of ZrO₂.

Effect of heat treatment on corrosion behavior of Mg-5Gd-3Y-0.5Zr alloy

The effects of different heat treatment processes on the microstructure and corrosion behavior of Mg-5Gd-3Y-0.5Zr (GW53K) magnesium alloy were studied by means of microanalysis, weight loss test and electrochemical test. The results show that appropriate heat treatment can improve the corrosion resistance of the alloy. Among the tested alloys, the T6-12 h alloy has the best corrosion resistance, which is mainly attributed to the morphology and distribution of the Mg-RE phase. The corrosion rate of the T4 alloy is similar to that of the T6-12 h alloy. The corrosion resistance of the T4 alloy may be reduced under long-term corrosion due to the existence of surface corrosion microcracks.

Microstructure and Corrosion of Cast Magnesium Alloy ZK60 in NaCl Solution

In this work, the effects of the microstructure and phase constitution of cast magnesium alloy ZK60 (Mg-5.8Zn-0.57Zr, element concentration in wt.%) on the corrosion behavior in aqueous NaCl (0.1 mol dm⁻³) were investigated by weight-loss measurements, hydrogen evolution tests, and electrochemical techniques. The alloy was found to be composed of α-Mg matrix, with large second-phase particles of MgZn₂ deposited along grain boundaries and a Zr-rich region in the central area of the grains. The large second-phase particles and the Zr-rich regions were more stable than the Mg matrix, resulting in a strong micro-galvanic effect. A filiform corrosion was found. It originated from the second-phase particles in the grain boundary regions in the early corrosion period. The filaments gradually occupied most areas of the alloy surface, and the general corrosion rate decreased significantly. Corrosion pits were developed under filaments. The pit growth rate decreased over time; however, it was about eight times larger than the general corrosion rate. A schematic model is presented to illustrate the corrosion mechanism.