Shouqiu Tang

Morphology modification of Mg2Si by Sr addition in Mg-4%Si alloy

A modification of Mg(2)Si in the hypereutectic Mg-4%Si alloy (mass fraction) with Sr was investigated. Two types of Mg(2)Si in the alloys were found: polygonal primary Mg(2)Si and Chinese script type eutectic Mg(2)Si. Adding Al-10% Sr master alloy to the Mg-4% Si alloy clearly reduced the average size of primary Mg(2)Si and changed the morphology of eutectic Mg(2)Si from Chinese script type to polyhedral or fine fibre shape. The refinement of primary Mg(2)Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles. The modification of eutectic Mg(2)Si results from the dissolved Sr, which alters the preferred growth manner of the eutectic.

Effects of scandium addition on the in vitro degradation behavior of biodegradable Mg–1.5Zn–0.6Zr alloy

Heretofore, recognitions of the systematic effects of scandium addition on corrosion behavior of biodegradable magnesium alloys are not yet clear. In the present study, a series of Mg–1.5Zn–0.6Zr–xSc (ZK21–xSc, x = 0, 0.2, 0.5, 1.0 wt.%) alloys were casted and investigated with respect to the immersion and electrochemical degradation behavior. The hydrogen evolution, pH monitoring, ion release and mass loss results demonstrated that ZK21–0.2Sc alloy exhibited the lowest corrosion rate. The surface morphology analyses displayed that an obvious uniform corrosion occurred in ZK21–xSc alloys with Sc content below 0.5, while localized corrosion occurred in ZK21–1.0Sc alloy. Corrosion potentials of ZK21–xSc alloys shifted toward more positive with the increasing Sc content. But ZK21–0.2Sc alloy exhibited the lowest corrosion current density and the largest corrosion film resistance. Compared with other developed Mg alloys, the ZK21–0.2Sc alloy demonstrated a superior degradation behavior.

Enhanced Corrosion Resistance of 6063 Aluminum in Surface Modification Using γ-Aminopropyl Triethoxysilane

The corrosion protection of 6063 aluminum with film of 3-aminopropyl triethoxysilane was studied in this paper. Electrochemical tests in neutral 3.5% (wt%) NaCl solution, scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), and confocal laser scanning microscope (CLSM) were performed. The result showed that the silane films could offer unexceptionable corrosion resistance to metal. A highly crosslinked and dense interfacial layer formed on the surface of the metal, which makes the substrate and the coating firmly combined to reduce the corrosion current density and inhibit the occurrence of corrosion. The film with bridging group had excellent hydrophobicity which can heavily restrict corrosion product proceeds at the interface.

Thermodynamic Description of the Al–Mg–Y System

The Al–Mg–Y system was critically assessed by means of the CALPHAD technique. The solution phases of liquid, face-centered cubic (FCC), body-centered cubic (BCC) and hexagonal close-packed (HCP) were modeled with Redlich–Kister equation. The thermodynamic models of compounds Al12Mg17, Al30Mg23 and Al3Mg2 in the Al–Mg system, AlY2, Al2Y3, AlY and Al3Y in the Al–Y system, as well as Mg24Y5 in the Mg–Y system were kept consistent with that of the corresponding binary systems. In order to reproduce the ternary solid solubility of previously determined isothermal section at 400 °C, an identical formula of (Al,Mg,Y)2(Al,Mg,Y) was used to model Al2Y phase in the Al–Y system and Mg2Y in the Mg–Y system. The ordered part of BCC phase, i.e. the BCC_B2 phase, was treated with a thermodynamic model of (Al,Mg,Y)0.5(Al,Mg,Y)0.5(Va)3. The ternary phase of Al4MgY was described as linear compound with sub-lattice model. On the basis of the optimized thermodynamic parameters of Al–Mg, Al–Y and Mg–Y systems in literature, the Al–Mg–Y system was optimized in present work. The currently calculated isothermal sections at 400 and 800 °C, as well as the liquidus surface projection agree well with the previous experimental data.