Study On Mg-Zn-RE-Zr Damping Magnesium Alloys

With the rapid development of modern industry, the harm of vibration and noise is growing. Magnesium alloys have excellent damping capacity and good mechanical properties. To develop high strength damping magnesium alloys as structural materials is of great significance for key structure components of lightweight, high strength and good damping.This research adopted composite rare earth reinforcement method to design the Mg-Zn-Y-Nd-Zr series magnesium alloys, and studied the effect of rare earth Y and Nd on structure, mechanical properties and damping capacities of magnesium alloys. And studied the heat treatment and hot extrusion process of the Mg-Zn-Y-Nd-Zr alloys and revealed the microstructure evolution, strengthening mechanism and damping mechanism of heat treated and extrude alloys.This study analyzed the microstructure, mechanical properties and damping performance of Mg-Zn-Y- Zr and Mg-Zn-Y-Nd-Zr alloy. The results show that when the Zn/Y ratio is 2, Mg- Zn-Y-Zr alloy can form I-Mg3YZn6 quasi-crystal and W-Mg3Y2Zn3 phases. Composite rare earth Y and Nd add can make W + I phases in Mg-Zn-Y-Zr alloy change to W phase, and precipitates more second phase. W phase is a important strengthening phase in Mg-Zn- Zr alloys, its content has a great influence on the mechanical properties of the alloy: when W phase content is 3.4%, Mg-Zn-Y-Nd-Zr alloy has the best mechanics, the tensile strength, yield strength a nd elongation increase to 198 MPa, 118 MPa and 18.3%, respectively; When W phase content is more than 3.4%, a large number of continuous network coarsening W phase occurs at grain boundaries of Mg-Zn-Y-Nd-Zr alloy, resulting in a sharp decrease in strength andducility.The solid solution treatment and aging treatment are applied on the studied Mg-Zn-Y-Nd-Zr alloys including Mg-2%Zn-0.5%Y-0.5%Nd-0.6%Zr(ZWE2) ? Mg-3%Zn-0.75%Y-0.75%Nd-0.6%Zr(ZWE3) and Mg-4%Zn-1%Y-1%Nd-0.6%Zr(ZWE4) alloys. The best solution treatment parameters are obtained: 525?×4h,525? ×8h,525?×12h, respectively. The results show that W phase would decompose during solution treatment, and tensile strength and elongation of ZWE3 and ZWE4 alloy get improved significantly. A large number of long-rod-shaped ZnZr phase precipitates in the solution treated alloys. After aging treatment, the phase composition of Mg-Zn-Y-Nd-Zr alloys consist of a large number of nano-scaled ?1??2 and Mg12 Nd phases. The tensile strength, yield strength and elongation of ZWE4 raise up to 256 mpa and 148 mpa and 13.4%. The deformation mechanisms of aged alloys include sliding and twin mixed mechanism, belonging to high elongation magnesium alloy. The solution treated Mg-Zn-Y-Nd-Zr alloys have tangled dislocations and a lot of precipitations, so the damping decreases sharply. Aged ZWE3 and ZWE4 alloys have plate-strip-shaped twin structure, their damping values are larger than that of corresponding solution treated one. Twin damping is a new damping mechanism in magnesium alloy.Finally, the extrusion process is carried out on the ZWE2 alloy. After hot extrusion, dynamic recrystallization occurs in the alloy, recrystallization grain size sharply reduced relatively, changing from 101?m to 6?m below. Under extrusion ratio of 9, extrusion temperature have little effect on the microstructure, due to the occurrence of local dynamic recrystallization, due to the work hardening effect, the extrude alloy has the highest yield strength and tensile strength, but incomplete recrystallization leads to the deterioration of the elongation. Under extrusion ratio of 16 and 25, complete dynamic recrystallization occurs in the alloy, the crystal grain grows and the yield strength and tensile strength of the alloy decrease, but the elongation increases. The best extrusion process for ZWE2 alloy is 300 ? extrusion temperature + extrusion ratio of 9, the maxium tensile strength, yield strength and elongation are 336 MPa, 288 MPa and 10.8%. The fracture mechanism of all extrude alloys belongs to ductile fracture.