Tiancai Xu

A novel microalloyed Mg–3Al–0.5Mn–0.5Sr (AMJ300) alloy was designed and prepared. Then the original structure of as-cast alloy was optimized by hot extrusion. The influence of extrusion on microstructure, corrosion and tensile properties of as-cast AMJ300 alloy were studied by OM, SEM, EDS, XRD, TEM, electrochemical workstation and tensile tests. The results indicated that α-Mg, Al₈Mn₅ and Al₄Sr phases constitute the AMJ300 alloy. Furthermore, the microstructure of alloy was further refined after extrusion, which indicates that the microstructural evolution during extrusion was governed by dynamic recrystallization. The fine and close of structure and the morphology change of intermetallic compounds greatly improved the corrosion resistance of AMJ300 alloy. The results of corrosion rate, corrosion current and corrosion morphology showed that the corrosion resistance of as-cast alloy could be significantly improved by extrusion. The main corrosion products of AMJ300 alloy in 3.5 wt.% NaCl solution was Mg(OH)₂. After extrusion, the tensile properties of AMJ300 alloy was significantly improved. The tensile strength reached 349 MPa, the yield strength reached 229 MPa, and the elongation reached 13.2%. Compared with the as-cast alloy, the tensile strength, the yield strength and the elongation increased by 218.1%, 248.9% and 173.7% respectively

The as-cast dual-phase Mg-9Li-3Al-xNd (x=0, 0.5, 1.0, 1.5, 2.0 and 3.0 wt.%, LA93-xNd) alloys were designed and prepared by vacuum melting, then the as-cast alloys processed by hot extrusion. The microstructures and mechanical properties of as-cast and as-extruded LA93-xNd alloys were investigated by the optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) with an Oxford energy-dispersive X-ray spectroscope (EDS), transmission electrical microscope (TEM) and uniaxial tension test. The addition of Nd led to the most significant grain refinement of Mg-9Li-3Al (LA93) alloy. The as-cast LA93 alloy was composed of α-Mg phase, β-Li phase and Li2MgAl intermetallic compound, and that Al2Nd and Al11Nd3 intermetallic compound generated when Nd added into the alloy. Nd was used to strengthen LA93 alloy by means of solid solution, grain refinement and precipitation. Among as-cast alloys, the tensile strength and elongation of LA93-1.0Nd alloy were the most outstanding, the tensile strength was 173 Mpa and the elongation was 36.8%. The mechanical properties of Mg-Li-Al-Nd alloy in extruded state was greatly improved compared with that in cast state, which was mainly because the extrusion weakened the defects left from cast state and improved the quality of alloy. The extruded alloy grains had been significantly refined. The ultimate tensile strength and elongation of as-extruded LA93-1.0Nd and LA93-1.5Nd alloys were 239 MPa and 27%, 255 MPa and 21%, respectively.

The hot deformation and dynamic recrystallization behavior of the dual-phase Mg-9Li-3Al-2Sr-2Y alloy had been investigated using a compression test. The typical dual-phase structure was observed, and average of grain size of as-homogenized alloy is about 110 µm. It mainly contains β-Li, α-Mg, Al₄Sr and Al₂Y phases. The dynamic recrystallization (DRX) kinetic was established based on an Avrami type equation. The onset of the DRX process occurred before the peak of the stress–strain flow curves. It shows that the DRX volume fraction increases with increasing deformation temperature or decreasing strain rate. The microstructure evolution during the hot compression at various temperatures and strain rates had been investigated. The DRX grain size became larger with the increasing testing temperature or decreasing strain rate because the higher temperature or lower strain rate can improve the migration of DRX grain boundaries. The fully recrystallized microstructure can be achieved in a small strain due to the dispersed island-shape α-Mg phases, continuous the Al₄Sr phases and spheroidal Al₂Y particles, which can accelerate the nucleation. The continuous Al₄Sr phases along the grain boundaries are very helpful for enhancing the corrosion resistance of the duplex structured Mg-Li alloy, which can prevent the pitting corrosion and filiform corrosion.