Effect of Sn Addition on Microstructure and Corrosion Behavior of As-Extruded Mg-5Zn-4Al Alloy

Estimation of mechanical properties of Mg-5Zn-0.5Al-xSn alloy based on virtual crystal approximation

First-principles calculations of multi-component alloys have been studied in detail. Herein, the first-principles calculations of Mg-5Zn-0.5Al-xSn alloys were performed by using the virtual crystal approximation (VCA) method. By calculating the lattice constants and elastic constants of the Mg-5Zn-0.5Al-xSn doping models, it was found that the mechanical properties and micro-hardness were related with the content of Sn. With the increase of Sn content, and the best ductility and the smallest micro-hardness were achieved at Sn = 2 wt.%. To verify the calculation results, the Mg-5Zn-0.5Al-xSn alloys were prepared and micro-hardness and tensile tests were conducted. The experiments demonstrate that the trends in mechanical properties obtained from the experiments are in agreement with the VCA computational results. These findings indicate that the VCA method has guiding significance in industries for rapid screening of high-performance Mg alloys.

Dry Sliding Wear and Corrosion Performance of Mg-Sn-Ti Alloys Produced by Casting and Extrusion

The aim of the present study is to investigate the role of Ti on corrosion and the wear properties of Mg-5Sn-xTi (x = 0, 0.15, 0.75, 1.5 wt.%) alloys. The samples were fabricated by conventional casting followed by hot extrusion, and the studies were examined by means of a pin-on-disc tribometer at various loads of 6, 10, and 20 N with constant sliding velocities of 0.04 m/s at ambient temperature. The corrosion performance, using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), was studied in a basic solution containing 3.5 wt.% NaCl. The observation indicated a drop in the wear rate with an increase in Ti, while the average coefficient of friction was raised in higher Ti contents compared to the base material. The sample with 0.75 wt.% Ti exhibited superior wear properties at 6 and 10 N of normal force, while the sample with 0.15 wt.% Ti presented better wear resistance for 20 N. Electrochemical test observations demonstrated that the Ti deteriorated the corrosion features of the Mg-5Sn alloy, owing to the galvanic effects of Ti. The Mg-5Sn alloy exhibited excellent corrosion behavior (corrosion potential (E_corr) = −1.45V and current density (I_corr) = 43.92 A/cm²). The results indicated the significant role of Ti content in modulating wear and corrosion resistance of the Mg-5Sn alloy.

The effects of Sn content on the corrosion behavior and mechanical properties of Mg-5Gd-3Y-xSn-0.5Zr alloys

The effects of Sn content on the corrosion behavior and mechanical properties of Mg-5Gd-3Y-0.5Zr alloy were studied by SEM, EDS, XRD and electrochemical testing. Results show that Sn can refine the grain size and promote the precipitation of Mg5(Gd,Y) phase. When the Sn content is 1.5-2 wt%, a needle-like Mg2Sn phase will be precipitated in the alloy. Mg-5Gd-3Y-1Sn-0.5Zr alloy had the lowest corrosion rate, which is attributed to the barrier effect of the grain boundary and dispersed Mg5(Gd,Y) phase on corrosion. However, the Mg2Sn phase formed by excessive Sn addition will accelerate galvanic corrosion. At the same time, Mg-5Gd-3Y-1Sn-0.5Zr alloy had best mechanical properties. In 1.5Sn and 2Sn alloys, the cleavage effect of the needle-like Mg2Sn phase on the matrix reduced mechanical properties.

The role of alloyed strontium in the microstructures and alkaline electrochemistry of Mg-5Al-4Sn alloys

In this study, strontium is used as an alloying element for improving the pitting resistance of Mg–5Al–4Sn based alloys in an alkaline solution. Potentiodynamic polarization measurements suggest that the addition of strontium increases the robustness of the pitting resistance as a result of the higher pitting potential and wider range of passive potential. Electrochemical impedance spectroscopy (EIS) confirms the formation of a solid passive film on the alloy surface due to a significant increase in the passive film and the charge transfer resistance, as well as lower film and double layer constant phase element magnitude values. Additionally, the potentiostatic polarisation results also show a lower passive current density and passive film stability, resulting in an increase in the breakdown time when the amount of strontium added to the alloy increases from 0.0 to 1.0 wt%. Furthermore, the scanning electron microscopy results indicate that insignificant corrosion is observed on alloy specimens containing strontium, whereas there is fierce corrosion on alloy based surfaces. This robust corrosion resistance could be attributed to the α-grain reduction and refined precipitates at the alloy grain boundaries, resulting in promoted formation of the passive film which is formed from a mixture of magnesium, aluminum and tin oxides/hydroxides, as confirmed by the X-ray photoelectron spectroscopy results.

The development of Mg–5Al–4Sn–xSr alloys with α-grain reduction, refined precipitates and pitting corrosion resistance by die casting.

Effect of Zn Content on the Microstructure and Mechanical Properties of Mg-Al-Sn-Mn Alloys

High performance Mg-6Al-3Sn-0.25Mn-xZn alloys (x = 0, 0.5, 1.0, 1.5, and 2.0 wt %) without rare earth were designed. The effects of different Zn contents on the microstructure and mechanical properties were systematically investigated. The addition of Zn obviously refines the as-cast alloys dendritic structure because of the increase in the number in the second phase. For the as-extruded alloys, an appropriate amount of Zn promotes complete recrystallization, thus increasing the grain size. As the Zn content increases, the texture gradually evolves into a typical strong basal texture, which means that the basal slip is difficult to initiate. Meanwhile, the addition of Zn promotes the precipitation of small-sized second phases, which can hinder the dislocation movement. The combination of texture strengthening and precipitation strengthening is the main reason for the improvement of alloys' strength.