Tiancai Xu

Microstructure and Mechanical Properties of Superlight Mg-Li-Al-Zn Wrought Alloy

Abstract Superlight alloys, including Mg-7Li-3Zn, Mg-7Li-3Al and Mg-7Li-1.5Al-1.5Zn, were prepared using a resistance furnace under the protection of argon atmosphere. The microstructures and phases of the alloys were studied by optical microscopy, scanning electronic microscopy (SEM), X-ray diffraction (XRD). The mechanical properties of these alloys were measured by a tensile tester. The results show that the Zn and Al added in Mg-Li alloy mainly dissolve in α-Mg phase and β-Li phase. However, there still exists a part of the Al and Mg compound such as Mg17Al12 which is mainly distributed discontinuously at α phase boundary while the most of them in the β phase are granular. The as-extruded Mg-7Li-3Al alloy has the maximum tensile strength and yield strength of 239 MPa (34% higher than the as-cast) and 178 MPa (31% higher than the as-cast), respectively, and the maximum elongation reaches to 27% (93% higher than the as-cast).

Dynamic Recrystallization Behavior and Corrosion Resistance of a Dual-Phase Mg-Li Alloy

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.

Comparative study on the microstructure and mechanical properties of Mg-Li-Al based alloys with yttrium and strontium addition

The effects of yttrium and strontium on the microstructure and mechanical properties of Mg-11Li-3Al magnesium alloy (LA113) are compared and analyzed. Microstructures and phases of the alloys were studied with optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of alloys were measured with tensile tester. The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA113 alloy. Al2Y and Al4Sr, etc. phases with different morphologies are verified and exist inside the grain or at the grain boundaries, which directly impact on the mechanical properties of LA113 alloy. The results of tensile tests show that, the as-extruded LA113-1Y-1Sr alloy obtains the optimal tensile property of which the tensile strength and elongation are 253.56 MPa and 18.12%, the tensile strength is increased by almost 25% compared with the asextruded LA113 alloy.