Xingrong Chu

Experimental investigation of pulse current on mechanical behaviour of AZ31 alloy

Abstract The effect of pulse current on the mechanical properties of AZ31 alloy is investigated through uniaxial tensile test at different temperatures. The electroplastic effect is evaluated by the change of ultimate strength. During tensile test, both microstructure evolution and fracture behaviour are sensitive to the applied deformation conditions. In this work, the influence of pulse current is discussed from the point of view of microstructure evolution and fracture characteristics. The experimental results show that the dynamic recrystallisation temperature of AZ31 is reduced by the pulse current and continuous dynamic recrystallisation is found at 100°C for tensile test with current. The data also indicate that the pulse current accelerates the precipitation and dissolved of the second phase particles in AZ31 alloy.

Research of initial dynamic recrystallisation for AZ31 alloy with pulse current

Abstract Tensile tests with pulse current for AZ31 alloy under room temperature and different voltages were carried out. Pulse current influence on the critical condition of initial dynamic recrystallisation for AZ31 alloy was investigated. The critical value was determined by one-parameter approach and validated by metallographic observation. The results showed that, with current voltage increased, the ultimate strength decreased, and the amount of strain hardening before reaching the ultimate strength decreased. When the voltage increases, high dynamic recrystallisation degree can be obtained, but due to the high electroplastic effect, the dynamic recrystallisation grain grows up and the material mechanical property deteriorates. The microstructure observation proved that the critical condition for initial dynamic recrystallisation can be determined with the one-parameter approach.

Electro-plastic effect on tensile deformation behaviour and microstructural mechanism of AZ31B alloy

The influences of electropulse on mechanical properties of AZ31B alloy were investigated by the electro-plastic (EP) tensile tests. The results show that the flow stress decreases with the increase of the root mean square (RMS) current density, while the elongation to fracture almost remains unchanged after it reaches a certain value. The higher peak current density can lead to a more potent EP effect when the RMS current density remains approximate. The results of microstructure analysis indicate that, the electropulse can reduce the dynamic recrystallisation temperature and promote the grain boundary sliding. The inverse eutectic reaction (α + β = L) will take place at the necking zone under high electropulse, which can optimise the deformation mechanism before the liquid phase is too much.

Experimental Investigation on Formability of AZ31B Magnesium Alloy V-Bending Under Pulse Current

In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy during electropulse-assisted (EPA) V-bending was investigated. The experimental results showed that pulse current can effectively reduce the springback and the bending force compared to the experiments without current. The frequency has a more significant influence on bending force and springback than electric current density. Electroplastic (EP) effect begins to work when pulse current parameters reach a threshold value. To explore the mechanism of EPA V-bending, the microstructure evolution and fracture surface of the bending specimen were studied. It was found that pulse current can promote the occurrence of dynamic recrystallization (DRX) of magnesium alloy compared to traditional hot forming process. The fracture mode of AZ31B under EPA V-bending evolves from brittle fracture to ductile fracture with increasing pulse current parameters. Based on the discussion of athermal and thermal effects of EP effect, the mechanism of pulse current to promote DRX is studied and athermal effect is proved to exist.

Experimental investigation on deep drawing behaviour of AZ31 alloy sheet under crank press

Abstract Deep drawing process of AZ31 alloy sheet was conducted under crank press, which is different from conventional drawing on hydraulic press with a lower speed. The optimum drawing condition was determined by the orthogonal test to improve the drawability of AZ31 alloy. Good formed specimens were obtained and their mechanical behaviours after drawing were investigated from the point of view of microstructure evolution, texture evolution and fracture appearance. The results showed that fine grain microstructure and weaken basal texture after deformation is attributed to the twin induced dynamic recrystallisation.