Papers by Author: Li Lin

Abstract: The effect of solid solution treatment at temperature of 415oC and different holding time prior aging at 168oC for 16 hours on the mechanical properties and microstructure of AZ81-4Gd magnesium alloy were analyzed by X-ray and SEM. The results demonstrated that with increasing the solid solution time the primary β-Mg17Al12 phase dissolve in the matrix eventually. While the holding time increases to 20 hrs, the primary β-Mg17Al12 phase was completely vanished, but Al2Gd phase kept unchanged with increasing the holding time. In the mean while, the volume fraction of the β-Mg17Al12 phase precipitated during aging increased at first with increasing the holding time then decreased. Moreover, subgrains and twins began to form within the α grain matrix when the solid solution time increased to 12hrs, and the subgains parallele with each other or in the shape of oval. Increasing the solid solution time to 20 hrs the microstructure change dramatically and consist of very fine recrystallized α grains. Futher increasing the holding time the recrystallized grain size increased accordingly. The mechanical properties testing results showed that when the solid solution time increased to 24 hrs the ultimate tensile strength of AZ81-4Gd magnesium alloy was 270 MPa and the elongation was 11.6% respectively.

Abstract: An AZ81 magnesium alloy, which was processed by hot extrusion in advance, was tested in the temperature range of 473 ~ 623 K and at various initial strain rates, ranging from 1×10-1 to 1×10-4 s-1. True stress-true strain curves under various temperatures and activation energy within different temperature range were investigated for the analysis of effect of temperature on superplastic behaviors. Elongation of the as-extruded AZ81 alloy increased with temperature when tested at the same initial strain rate. Elongation values, obtained at the same initial strain rate of 1×10-3 s-1, were 94% at 473K and 446% at 623K, respectively. Deformation mechanisms varied with increasing temperature, from the grain boundary sliding (GBS) accommodated by grain boundary diffusion to the GBS accommodated by lattice diffusion, transition temperature was 573 K.

Abstract: Microstructure evolution and superplastic behaviors of ZK40 magnesium alloy were investigated in the temperature range of 473 ~ 623 K. Twinning occurred significantly after being processed by equal channel angular pressing (ECAP) for one pass through the die, the mean grain size was 5.6 µm. Finer grains can be obtained after further processing through ECAP, the average grain size of the alloy processed by ECAP for three passes was as low as 0.8 µm; this alloy exhibited low temperature superplasticity at 473 ~ 523 K, elongations at an initial strain rate of 1×10-3 s-1 were 260 % at 473 K and 612 % at 523 K, respectively. The incompatibility between fine and coarse grains was thought to be unfavorable to the improvement of superplasticity. Low temperature superplasticity of the as-ECAP ZK40 alloy can be attributed to the relatively finer grain size and the homogeneity of microstructure.

Abstract: Bulk AZ91HP rods with a diameter of 8mm were prepared by copper mould casting. The microstructure and mechanical properties have been studied. The compressive strength, yield strength, elongation and microhardness of the rapidly solidified AZ91HP alloy are 392MPa, 183 MPa, 3.6% and HV87, respectively. It results from grain refinement and reinforcement of β-Mg17Al12 phase.